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Dick Proenneke retired at age 50 in 1967 and decided to build his own cabin on the shore of Twin Lakes. The first summer he scouted for the best cabin site, and cut and peeled the logs he would need for his cabin. Dick Proenneke returned the next summer to finish the cabin where he lived for over 30 years. Dick filmed his adventures, and Bob Swerer later turned the film into a video so we can all watch this amazing man build his cabin by hand.

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Solar Energy 
Projects for the 
HomeBrewPower
HomeBrewPower Series 
Bionics for the HomeBrewPower: 25 Build-it-Yourself 
Projects 
Electronic Circuits for the HomeBrewPower: 57 Lessons 
with Projects 
Electronic Gadgets for the HomeBrewPower: 
28 Build-it-Yourself Projects 
Electronic Games for the HomeBrewPower 
Electronic Sensors for the HomeBrewPower: 
54 Electrifying Projects 
50 Awesome Auto Projects for the HomeBrewPower 
50 Model Rocket Projects for the HomeBrewPower 
Mechatronics for the HomeBrewPower: 
25 Build-it-Yourself Projects 
MORE Electronic Gadgets for the HomeBrewPower: 
40 NEW Build-it-Yourself Projects 
101 Spy Gadgets for the HomeBrewPower 
123 PIC® Microcontroller Experiments for the Evil 
Genius 
123 Robotics Experiments for the HomeBrewPower 
PC Mods for the HomeBrewPower: 25 Custom Builds to 
Turbocharge Your Computer 
Solar Energy Projects for the HomeBrewPower 
25 Home Automation Projects for the HomeBrewPower
GAVIN D. J. HARPER 
Solar Energy 
Projects for the 
HomeBrewPower 
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Singapore Sydney Toronto
Copyright © 2007 by The HomeBrewPower Companies, Inc. All rights reserved. Manufactured in the United States of America. Except as permitted under 
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Professional 
Want to learn more?
To the late Mr. P. Kaufman 
who never failed to make science exciting

1 Why Solar? 1 
2 The Solar Resource 9 
3 Positioning Your Solar Devices 17 
Project 1: Build a Solar-Powered Clock! 20 
Project 2: Build Your Own Heliodon 22 
Project 3: Experimenting with Light 
Rays and Power 25 
4 Solar Heating 27 
Project 4: Build Your Own Flat 
Plate Collector 31 
Project 5: Solar Heat Your Swimming 
Pool 33 
Project 6: Useful Circuits for Solar 
Heating 35 
5 Solar Cooling 39 
Project 7: Solar-Powered Ice-Maker 42 
6 Solar Cooking 45 
Project 8: Build a Solar Hot Dog Cooker 46 
Project 9: Build a Solar Marshmallow 
Melter 48 
Project 10: Cook Eggs on Your Driveway 
Using the Sun 49 
Project 11: Build a Solar Cooker 50 
Project 12: Build a Solar Camping 
Stove 51 
7 Solar Stills 55 
Project 13: Build a Window-Sill 
Demonstration Solar Still 56 
Project 14: Build a Pit-Type Solar Still 57 
Project 15: Build a Solar Basin Still 58 
8 Solar Collectors 61 
Project 16: Build Your Own “Solar 
Death Ray” 64 
Project 17: Build Your Own Parabolic 
Dish Concentrator 69 
Project 18: Experiment with Fresnel 
Lens Concentrators 72 
9 Solar Pumping 75 
Project 19: Build a Solar-Powered 
Fountain 76 
10 Solar Photovoltaics 81 
Project 20: Grow Your Own “Silicon” 
Crystals 85 
Project 21: Build Your Own 
“Thin-Film” Solar Cell 87 
Project 22: Experimenting with the 
Current–Voltage Characteristics 
of a Solar Cell 92 
Project 23: Experimenting with 
Current–Voltage Characteristics 
of Solar Cells in Series 93 
Project 24: Experimenting with 
Solar Cells in Parallel 93 
Project 25: Experiment with the 
“Inverse Square Law” 94 
Project 26: Experimenting with 
Different Types of 
Light Sources 96 
Project 27: Experimenting with Direct 
and Diffuse Radiation 96 
Project 28: Measurement of 
“Albedo Radiation” 99 
11 Photochemical Solar Cells 105 
Project 29: Build Your Own 
Photochemical Solar Cell 107 
12 Solar Engines 113 
Project 30: Build a Solar Bird 
Engine 113 
Project 31: Make a Radial Solar 
Can Engine 116 
vii 
Contents 
For more information about this title, click here
viii Contents 
13 Solar Electrical Projects 119 
Project 32: Build Your Own Solar 
Battery Charger 119 
Project 33: Build Your Own Solar 
Phone Charger 120 
Project 34: Build Your Own 
Solar-Powered Radio 123 
Project 35: Build Your Own 
Solar-Powered Torch 124 
Project 36: Build Your Own Solar- 
Powered Warning Light 126 
Project 37: Build Your Own Solar- 
Powered Garden Light 127 
14 Tracking the Sun 129 
Project 38: Simple Solar Tracker 130 
15 Solar Transport 135 
Project 39: Build Your Own Solar Car 137 
Project 40: Hold Your Own Solar 
Car Race 142 
Project 41: Souping Up Your 
Solar Vehicle 143 
Project 42: Supercharge Your 
Solaroller 143 
Project 43: Build Your Own Solar 
Airship 146 
16 Solar Robotics? 149 
Project 44: Assembling Your 
Photopopper Photovore 153 
17 Solar Hydrogen Partnership 161 
Project 45: Generating Hydrogen 
Using Solar Energy 164 
Project 46: Using Stored Hydrogen 
to Create Electricity 168 
18 Photosynthesis—Fuel from the Sun 171 
Project 47: Proving Biofuel Requires 
Solar Energy 177 
Project 48: Proving Biofuel Requires 
Water 177 
Project 49: Looking at the Light- 
Absorption Properties of 
Chlorophyll 178 
Project 50: Make Your Own Biodiesel 180 
Appendix A: Solar Projects on the Web 185 
Appendix B: Supplier’s Index 188 
Index 195
Gavin Harper’s book Solar Energy Projects for the 
HomeBrewPower is a “must read” for every sentient 
human on this planet with a conscience, a belief in 
the bottom line, or a simple belief in the future of 
humanity. 
At a time when such a book should be offered 
as suggested reading for the 19-year-old 
Gavin Harper, he’s bucking the trend by actually 
being the author. Okay, so he’s written a book on 
solar energy you say, big deal you say. You would 
be wrong. Not only is this Gavin’s fourth book, it 
is nothing short of pure genius. 
To be able to write about solar energy is one thing. 
But to possess the ability to put the knowledge of 
solar energy into layman’s terms, while including 
examples of do-it-yourself projects which make 
the practical applications obvious, gives this boy 
genius the “street cred” (industry savvy) he so very 
much deserves. 
This is a “how-to” book, which debunks the 
myth that “these things are decades away,” and, 
without exception, should be in every classroom 
under the same sun. 
So crack this book, turn on your solar light, and 
sit back for a ride into our “present”… as in “gift” 
from God. 
Willie Nelson 
ix 
Foreword 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
x
There are always a lot of thank-yous to be said with 
any book, and this one is no exception. There are a 
lot of people that I would like to thank immensely 
for material, inspiration, ideas, and help—all of 
which have fed in to make this book what it is. 
First of all, a tremendous thank-you to the staff 
and students of the MSc. Architecture: Advanced 
Environmental & Energy Studies course at the 
Centre for Alternative Technology, U.K. I never 
cease to be amazed by the enthusiasm, passion, 
and excitement members of the course exude. 
I’d like to say a big thank-you to Dr. Greg P. 
Smestad, for his help and advice on photochemical 
cells. Dr. Smestad has taken leading-edge research, 
straight from the lab, and turned it into an accessible 
experiment that can be enjoyed by young scientists 
of all ages. I would also like to thank Alan 
Brown at the NASA Dryden Flight Research 
Center for the information he provided on solar 
flight for Chapter 15. 
Also a big thank-you to Ben Robinson and the 
guys at Dulas Ltd. for their help in procuring 
images, and for setting a great example by showing 
how companies can be sustainable and ethical. 
I’d also like to thank Hubert Stierhof for sharing 
his ideas about solar Stirling engines, and Jamil 
Shariff for his advice on Stirling engines and for 
continuing to be inspirational. 
Thanks also to Tim Godwin and Oliver 
Sylvester-Bradley at SolarCentury, and to Andrew 
Harris at Schuco for sharing with me some of their 
solar installations. 
An immense thank-you to Dave and Cheryl 
Hrynkiw and Rebecca Bouwseman at Solarbotics 
for sharing their insight on little solar-powered 
critters, and for providing the coupon in the back 
of the book so that you can enjoy some of their 
merchandise for a little less. 
A massive thank-you to Kay Larson, Quinn 
Larson, Matt Flood, and Jason Burch at 
Fuelcellstore.com for helping me find my way 
with fuel cells, and for being inspirational and letting 
me experiment with their equipment. It would 
also be wrong not to mention H2 the cat, who was 
terrific company throughout the process of learning 
about fuel cells. 
Also, many thanks to Annie Nelson, and Bob 
and Kelly King of Pacific Biodiesel for providing 
me with some amazing opportunities to learn about 
biodiesel. 
Thanks to Michael Welch at Home Power 
magazine, and also to Jaroslav Vanek, Mark 
“Moth” Green, and Steven Vanek, the designers of 
the fantastic solar ice-maker featured in Chapter 5. 
Their solar-powered ice-maker has already proven 
its immense worth in the developing world … and 
if you guys at home start building them at home 
and switching off your air-con and freezers, they 
stand to be a big hit in the developed world as well. 
A big thank-you to my grandfather, who has 
seen the mess upstairs and manages to tolerate it, 
to my grandmother who hears about the mess 
upstairs and does not realize its magnitude, and to 
Ella who does a good job of keeping the mess 
within sensible limits—and knows when to keep 
quiet about it. Thanks are also long overdue to my 
dad, who is always immensely helpful in providing 
practical advice when it comes to how to build 
things, and to my mum who manages to keep life 
going when I have got my head in a laptop. 
A huge thank-you to Judy Bass, my fantastic 
editor in New York who has been great throughout 
the trials and tribulations of bringing this book to 
print, and to the tremendous Andy Baxter (and the 
rest of his team at Keyword) who has managed to 
stay cool as a cucumber and provide constant reassurance 
throughout the editing process. 
Acknowledgments 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
Why Solar? 
Chapter 1 
Our energy 
In everyday life, we consume a tremendous 
amount of energy. Our lives are styled around 
consumption—consumption of natural resources 
and consumption of energy. 
Figure 1-1 dramatically illustrates where all of 
this energy goes. 
These figures are for a U.K. lifestyle, but we can 
take this as being representative for people who 
live in the “developed world.” 
The bulk of our energy consumption goes on 
space heating—58%—this is something that can 
easily be provided for with passive solar design. 
Next is water heating, which requires 24% of the 
energy which we use—again, we will see in this 
book how we can easily heat water with solar energy. 
So already we have seen that we can meet 82% 
of our energy needs with solar technologies! 
The next 13% of our energy is used to provide 
electrical power for our lights and home. In 
Chapter 10 on solar photovoltaics, we will see how 
we can produce clean electricity from solar energy 
with no carbon emissions. 
The remaining 5% is all used for cooking— 
again we will see in this book how easy it is to 
cook with the power of the sun! 
So we have seen that all of our energy needs can 
be met with solar technologies. 
Why solar? 
The short answer to this question, albeit 
not the most compelling is “Why not solar?” 
Figure 1-1 Domestic energy use. Information extracted from DTI publication “Energy Consumption in the United 
Kingdom.” You can download this information from www.dti.gov.uk. 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
Solar energy is clean, green, free, and best of all, 
isn’t going to be going anywhere for about the next 
five billion years—now I don’t know about you, 
but when the sun does eventually expire, I for one 
will be pushing up the daisies, not looking on with 
my eclipse glasses. 
For the longer, more compelling answer, you are 
going to have to read the rest of this chapter. At the 
end, I hope that you will be a solar convert and be 
thinking of fantastic ways to utilize this amazing, 
environmentally friendly, Earth-friendly technology. 
If we look at North America as an example, we 
can see that there is a real solar energy resource 
(Figure 1-2). While the majority of this is concentrated 
in the West, there is still enough solar energy 
to be economically exploited in the rest of the 
U.S.A.! 
Renewable versus 
nonrenewable 
At present, the bulk of our energy comes from 
fossil fuels—gas, coal, and oil. Fossil fuels are 
hydrocarbons, that is to say that if we look at 
them chemically, they are wholly composed of 
hydrogen and carbon atoms. The thing about 
hydrocarbons is that, when combined with the 
oxygen in the air and heat, they react exothermically 
(they give out heat). This heat is useful, 
and is used directly as a useful form of energy in 
itself, or is converted into other forms of energy 
like kinetic or electrical energy that can be used 
to “do some work,” in other words, perform a 
useful function. 
2 Why Solar? 
Figure 1-2 North American solar resource. Image courtesy Department of Energy.
So where did all these 
fossil fuels come from . . . 
and can’t we get some 
more? 
OK, first of all, the answer is in the question— 
fossils. Fossil fuels are so named because they are 
formed from the remains of animals and plants that 
were around a loooooong time ago. The formation 
of these fuels took place in the carboniferous period 
which in turn was part of the Paleozoic era, around 
360 to 286 million years ago. This would have been 
an interesting time to live—the world was covered 
in lots and lots of greenery, big ferns, lush verdant 
forests of plants. The oceans and seas were full of 
algae—essentially lots of small green plants. 
Although there are some coal deposits from 
when T-Rex was king, in the late cretaceous period 
around 65 million years ago, the bulk of fossil 
fuels were formed in the carboniferous period. 
So what happened to 
make the fossil fuels? 
Well, the plants died, and over time, layers of rock 
and sediment and more dead stuff built up on top 
of these carbon-rich deposits. Over many years, the 
tremendous heat and pressure built up by these 
layers compressed the dead matter 
We have only recently 
started to worry about 
fossil fuels—surely we 
have time yet? 
This is an incorrect assumption. For some time, 
people have prophesized the end of the fossil fuel age. 
When the Industrial Revolution was in fullswing 
Augustin Mouchout wondered whether the 
supply of fossil fuels would be able to sustain the 
Industrial Revolution indefinitely. 
“Eventually industry will no longer find in 
Europe the resources to satisfy its prodigious 
expansion. Coal will undoubtedly be used up. 
What will industry do then?” 
Fossil fuel emissions 
Take a peek at Figure 1-3. It is pretty shocking 
stuff! It shows how our fossil fuel emissions have 
increased dramatically over the past century—this 
massive amount of carbon dioxide in the atmosphere 
has dire implications for the delicate balance 
of our ecosystem and could eventually lead to runaway 
climate change. 
Hubbert’s peak and 
Peak Oil 
Back in 1956 an American geophysicist by the 
name of Marion King Hubbert presented a paper to 
the American Petroleum Institute. He said that oil 
production in the U.S.A. would peak toward the 
end of the 1960s, and would peak worldwide in the 
year 2000. In fact, U.S. oil production did peak at 
the beginning of the 1970s, so this wasn’t a bad 
prediction; however, the rest of the theory contains 
a dire warning. 
The theory states that production of fossil fuels 
follows a bell-shaped curve, where production 
begins to gradually increase, then as the technology 
becomes mainstream there is a sharp upturn in 
production, followed by a flattening off when production 
has to continue against rising costs. As the 
costs of extraction increase, production begins to 
plateau, and then fall—falling sharply at first, and 
then rapidly. 
Why Solar?
This is illustrated in Figure 1-4. 
This means that, if we have crossed the peak, 
our supplies of fossil fuels are going to begin 
to drop rapidly—when you think about how 
reliant we are on fossil fuels, this means that 
there is going to be a rapid impact on our way 
of life. 
So have we crossed the 
peak, and is there any 
evidence to support this? 
The International Energy Agency has stated that 
energy production is in decline in 33 out of the 48 
largest world oil producers. So, probably yes. 
In the same way that there is Peak Oil, there is 
also Peak Coal, Peak Gas and Peak Uranium. All 
of these resources are in finite supply and will not 
last forever. 
This means that those who believe that heavy 
investment in nuclear is the answer might be 
in for a shock. Nuclear has been touted by many 
as a means of plugging the “energy hole” left 
when fossil fuels run out; however, everyone 
in the world is facing the same problems—if 
everyone switches to nuclear power, the rate at 
which uranium is consumed will greatly increase. 
4 Why Solar? 
Figure 1-3 How our fossil fuel emissions have increased. 
Figure 1-4 Depiction of the “Peak Oil” scenario.
A few other reasons 
why nuclear is a dumb 
option 
Nuclear power really is pretty dangerous—talking 
about nuclear safety is a bit of a myth. Nuclear 
power stations are a potential target for terrorists, 
and if we want to encourage a clean, safe world, 
nuclear is not the way to go. 
Nuclear makes bad financial sense. When the 
fledgling nuclear power industry began to build 
power stations, the industry was heavily subsidized 
as nuclear was a promising new technology 
that promised “electricity too cheap to meter.” 
Unfortunately, those free watts never really materialized—
I don’t know about you, but my power 
company has never thrown in a few watts produced 
cheaply by nuclear power. Solar on the other hand 
is the gift that keeps on giving—stick some photovoltaics 
on your roof and they will pump out free 
watts for many years to come with virtually zero 
maintenance. 
Decommissioning is another big issue—just 
because you don’t know what to do with something 
when you finish with it isn’t an argument to 
ignore it. Would you like a drum of nuclear waste 
sitting in your garden? All the world round, we 
haven’t got a clue where to stick this stuff. The 
U.S.A. has bold plans to create Yucca mountain, a 
repository for nuclear waste—but even if this happens, 
the problem doesn’t go away—it is simply 
consolidated. 
Environmental 
responsibility 
Until cheap accessible space travel becomes a 
reality, and let’s face it, that’s not happening soon, 
we only have one planet. Therefore, we need to 
make the most of it. The earth only has so many 
resources that can be exploited, when these run 
out we need to find alternatives, and where there 
are no alternatives then we will surely be very 
stuck. 
Mitigating climate change 
It is now widely acknowledged that climate change 
is happening, and that it is caused by man-made 
events. Of course, there is always the odd scientist, 
who wants to wave a flag, get some publicity and 
say that it is natural and that there is nothing we 
can do about it, but the consensus is that the 
extreme changes that we are seeing in recent times 
are a result of our actions over the past couple of 
hundred years. 
Sir David King, the U.K.’s Chief Scientific 
Advisor says that climate change is “the most 
severe problem that we are facing today—more 
serious even than the threat of terrorism.” 
So how can we use solar 
energy? 
When you start to think about it, it is surprising 
how many of the different types of energy sources 
around us actually come from the sun and solardriven 
processes. Take a look at Figure 1-5 which 
illustrates this. 
We can see how all of the energy sources in this 
figure actually come from the sun! Even the fossil 
fuels which we are burning at an unsustainable rate 
at the moment, actually originally came from the 
sun. Fossil fuels are the remains of dead animal 
and plant matter that have been subject to extreme 
temperature and pressure over millions of years. 
Those animals fed on the plants that were around 
at the time (and other animals) and those plants 
grew as a result of the solar energy that was falling 
on the earth. 
Why Solar?
Biomass therefore is a result of solar energy— 
additionally, biomass takes carbon dioxide out of 
the atmosphere. When we burn it we simply put 
back the carbon dioxide that was taken out in the 
first place—the only carbon emissions are a result 
of processing and transportation. 
Looking at hydropower, you might wonder 
how falling water is a result of the sun, but it is 
important to note that the hydrological cycle 
is driven by the sun. So we can say that hydropower 
is also the result of a solar-driven 
process. 
Wind power might seem disconnected from solar 
energy; however, the wind is caused by air rushing 
from an area of high pressure to an area of low 
pressure—the changes in pressure are caused by 
6 Why Solar? 
Figure 1-5 Energy sources. Image courtesy Christopher Harper.
the sun heating air, and so yet again we have 
another solar-driven process! 
Tidal power is not a result of the sun—the tides 
that encircle the earth are a result of the gravitational 
pull that the moon has on the bodies of 
water that cover our planet. However, wave power 
which has a much shorter period, is a result of 
the wind blowing on the surface of the water—just 
as the wind is a solar-driven process, so is wave 
power. 
So where does our 
energy come from at 
the moment? 
Let’s look at where the U.S.A. gets its energy 
from—as it is representative of many western 
countries. 
If we look at the U.S.A.’s energy consumption, 
we can see (Figure 1-6) that most of our energy at 
the moment is produced from fossil fuels. This is a 
carbon-intensive economy which relies on imports 
of carbon-based fossil fuels from other countries, 
notably the Middle East. Unfortunately, this puts 
America in a position where it is dependent on oil 
imported from other countries—politically, this is 
not the best position to be in. Next we look at hydropower, 
which produces around 7% of America’s 
electricity. Things like aluminum smelters, which 
require large inputs of electricity, are often located 
near to hydropower schemes because they produce 
an abundance of cheap electricity. Finally the 
“others” account for 5% of America’s electricity 
production. 
It is these “others” that include things such as 
solar power, wind powers and wave and tidal 
power. It is this sector that we need to grow in 
order to make energy supply more sustainable and 
decrease our reliance on fossil fuels. 
This book is primarily concerned with development 
of the solar energy resource. 
The nuclear lobby argue that nuclear is “carbon 
neutral” as the plants do not produce carbon dioxide 
in operation; however, this does not take into 
account the massive input of energy used to construct 
the plant, move the fuel, and decommission the 
plant. All of this energy (generally speaking) 
comes from high-carbon sources. 
So we must look at the two remaining alternatives 
to provide our energy—hydro and “others.” 
Why Solar? 
Figure 1-6 Where the United States’ energy comes from.
There are limits to how much extra hydroelectric 
capacity can be built. Hydroelectricity relies on 
suitable geographic features like a valley or basin 
which can be flooded. Also, there are devastating 
effects for the ecosystems in the region where the 
hydro plant will be built, as a result of the largescale 
flooding which must take place to provide 
the water for the scheme. 
Micro-hydro offers an interesting alternative. 
Rather than flooding large areas, micro-hydro 
schemes can rely on small dams built on small 
rivers or streams, and do not entail the massive 
infrastructure that large hydro projects do. While 
they produce a lot less power, they are an interesting 
area to look at. 
So all this is new right? 
Nope . . . Augustin Mouchot, a name we will see a 
couple of times in this book said in 1879: 
“One must not believe, despite the silence of 
modern writings, that the idea of using solar heat 
for mechanical operations is recent.” 
8 Why Solar?
The Solar Resource 
Chapter 2 
The sun 
Some 92.95 × 106 miles away from us, or for those 
working in metric 149.6 × 106 km away from us is 
the sun (Figure 2-1). To imagine the magnitude of 
this great distance, think that light, which travels at 
an amazing 299,792,458 meters per second, takes a 
total of 8.31 minutes to reach us. You might like to 
do a thought experiment at this point, and imagine 
yourself traveling in an airplane across America. 
At a speed of around 500 miles per hour, this 
would take you four hours. Now, if you were traveling 
at the speed of light, you could fly around the 
earth at the equator about seven and a half times in 
one second. Now imagine traveling at that speed 
for 8.31 minutes, and you quickly come to realize 
that it is a long way away. 
Not only is it a long way away, but it’s also 
pretty huge! 
It has a diameter of 864,950 miles; again, if you 
are working to metric standards that equates to 
1.392 million km. 
Although the sun is incredibly far away—it is 
also tremendously huge! This means that although 
you would think that relatively little solar energy 
reaches us, in fact, the amount of solar radiation 
that reaches us is equal to 10,000 times the 
annual global energy consumption. On average, 
1,700 kWh per square meter is insolated every 
year. 
Now doesn’t it seem a silly idea digging miles 
beneath the earth’s surface to extract black rock 
and messy black liquid to burn, when we have this 
amazing energy resource falling on the earth’s 
surface? 
As the solar energy travels on its journey to the 
earth, approximately 19% of the energy is 
absorbed by the atmosphere that surrounds the 
earth, and then another 35% is absorbed by clouds. 
Once the solar energy hits the earth, the journey 
doesn’t stop there as further losses are incurred in 
the technology that converts this solar energy to a 
useful form—a form that we can actually do some 
useful work with. 
How does the sun work? 
The sun is effectively a massive nuclear reactor. 
When you consider that we have such an incredibly 
huge nuclear reactor in the neighborhood 
already, it seems ridiculous that some folks want to 
build more! 
The sun is constantly converting hydrogen to 
helium, minute by minute, second by second. 
Figure 2-1 The sun. Image courtesy NASA. 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
But what stops the sun from exploding in a 
massive thermonuclear explosion?—simple 
gravity! The sun is caught in a constant struggle 
between wanting to expand outwards as a result of 
the energy of all the complex reactions occurring 
inside it, and the massive amount of gravity as a 
result of its enormous amount of matter, which 
wants to pull everything together. 
All of the atoms inside the sun are attracted to 
each other, this produces a massive compression 
which is trying to “squeeze” the sun inwards. 
Meanwhile, the energy generated by the nuclear 
reactions taking place is giving out heat and energy 
which wants to push everything outwards. Luckily 
for us, the two sets of forces balance out, so the 
sun stays constant! 
Structure of the sun 
Figure 2-2 illustrates the structure of the sun—now 
let’s explain what some of those long words mean! 
Starting from the center of the sun we have the 
core, the radiative zone, the convective zone, the 
photosphere, the chromosphere, and the corona. 
The core 
The core of the sun possesses two properties which 
create the right climate for nuclear fusion to 
occur—the first is incredibly high temperature 
15 million degrees Celsius (I don’t envy the poor 
chap who had to stand there with a thermometer 
to take the reading) and the second is incredibly 
high pressure. As a result of this nuclear fusion 
takes place. 
In nuclear fusion, you take a handful of hydrogen 
nuclei—four in fact, smash them together and 
end up with one helium nucleus. 
There are two products of this process—gamma 
rays which are high-energy photons and neutrinos, 
one of the least understood particles in the universe, 
which possess no charge and almost no 
mass. 
10 The Solar Resource 
Figure 2-2 The structure of the sun. Image courtesy NASA.
The radiative zone 
Next out from the core is the radiative zone. This 
zone is so named because it is the zone that emits 
radiation. A little bit cooler, the temperature in the 
radiative zone ranges from 15 million to 1 million 
degrees Celsius (even at that temperature though, 
I still wouldn’t have liked to have been the one 
holding the thermometer). 
What is particularly interesting about the 
radiative zone, is that it can take millions of years 
for a photon to pass through this zone to get to the 
next zone, aptly named the convective zone! 
The convective zone 
This zone is different, in that the photons now 
travel via a process of convection—if you remember 
high school physics, you will recollect that 
convection is a process whereby a body makes its 
way to a region of lower temperature and lower 
pressure. The boundary of this zone with the radiative 
zone is of the order of a million degrees 
Celsius; however, toward the outside, the temperature 
is only a mere 6,000°C (you still wouldn’t 
want to hold the thermometer even with asbestos 
gloves). 
The photosphere 
The next region is called the photosphere. This is 
the bit that we see, because this is the bit that 
produces visible light. Its temperature is around 
5,500°C which is still mighty hot. This layer, 
although relatively thin in sun terms is still around 
300 miles thick. 
The chromosphere 
Sounding like a dodgy nightclub, the chromosphere 
is a few thousand miles thick, and the 
temperature rises in this region from 6,000°C to 
anywhere up to 50,000°C. This area is full of 
excited hydrogen atoms, which emit light toward 
the red wavelengths of the visible spectrum. 
The corona 
The corona, which stretches for millions of miles 
out into space, is the outer layer of the sun’s 
atmosphere. The temperatures here get mighty hot, 
in fact up to a million degrees Celsius. Some of the 
features on the surface of the sun can be seen in 
Figure 2-2, but they are described in more detail in 
the next section and Figure 2-3. 
Features of the sun 
Now we have seen the inner machinations of the 
sun, we might like to take a look at what goes on 
on the surface of the sun, and also outside it in the 
immediate coronal region. 
Coronal holes form where the sun’s magnetic 
field lies. Solar flares, also known as solar prominences, 
are large ejections of coronal material into 
space. Magnetic loops suspend the material from 
these prominences in space. Polar plumes are 
11 
The Solar Resource 
Figure 2-3 Features on the sun’s surface. Image 
courtesy NASA.
altogether smaller, thinner streamers that emanate 
from the sun’s surface. 
The earth and the sun 
Now we have seen what goes on at the source, we 
now need to explore what happens after that solar 
energy travels all the way through space to reach 
the earth’s orbit. 
Outside the earth’s atmosphere, at any given 
point in space, the energy given off by the sun 
(insolation) is nearly constant. On earth, however, 
that situation changes as a result of: 
. The earth changing position in space 
. The earth rotating 
. The earth’s atmosphere (gases, clouds, and dust) 
The gases in the atmosphere remain relatively 
stable. In recent years, with the amount of pollution 
in the air, we have noticed a phenomenon 
known as global dimming, where the particulate 
matter resulting from fossil fuels, prevents a small 
fraction of the sun’s energy from reaching the 
earth. 
Clouds are largely transient, and pass from place 
to place casting shadows on the earth. 
When we think about the earth and its orbit, we 
can see how the earth rotates upon its axis, which 
is slightly inclined in relation to the sun. As the 
earth rotates at a constant speed, there will be 
certain points in the earth’s orbit when the sun 
shines for longer on a certain part of the earth— 
and furthermore, because of the earth’s position in 
space, that part of the world will tend to be nearer 
to the sun on average over the period of a day. This 
is why we get the seasons—this is illustrated in 
Figure 2-4. 
As a result of the sun appearing to be in a different 
place in the sky, we may need to move our 
solar devices to take account of this. Figure 2-5 
illustrates how a flat plate collector may need to 
be moved at different times of the year to take 
account of the change in the sun’s position in order 
to harness energy effectively. 
So how can we harness 
solar energy? 
Thinking about it, more or less all of our energy 
has come either directly or indirectly from the sun 
at one point or another. 
12 The Solar Resource 
Figure 2-4 The sun and seasons.
Solar power 
Solar-powered devices are the most direct way of 
capturing the sun’s energy, harnessing it, and 
turning it into something useful. These devices 
capture the sun’s energy and directly transform it 
into a useful energy source. 
Wind power 
The heat from the sun creates convective currents 
in our atmosphere, which result in areas of high 
and low pressure, and gradients between them. The 
air rushing from place to place creates the wind, 
and using large windmills and turbines, we can 
collect this solar energy and turn it into something 
useful—electricity. 
Hydropower 
The sun drives the hydrological cycle, that is to say 
the evaporation of water into the sky, and precipitation 
down to earth again as rain. What this means 
is that water which was once at sea level can end 
up on higher ground! We can collect this water at a 
high place using a dam, and then by releasing the 
water downhill through turbines, we can release 
the water’s gravitational potential energy and turn 
it into electricity. 
Biomass 
Rather than burning fossil fuels, there are certain 
crops that we can grow for energy which will 
replace our fossil fuels. Trees are biomass, they 
produce wood that can be burnt. Sugarcane can 
also be grown and be turned into bio-ethanol, 
which can be used in internal combustion engines 
instead of gasoline. Oils from vegetable plants can 
in many cases be used directly in diesel engines or 
reformed into biodiesel. The growth of all of these 
plants was initiated by the sun in the first place, 
and so it can be seen that they are derived from 
solar energy. 
Wave power 
Wave power is driven by the winds that blow over 
the surface of large bodies of water. We have seen 
how the wind is produced from solar energy; 
however, we must be careful to distinguish wave 
power from tidal power, which is a result of the 
gravitational attraction of the moon on a large 
body of water. 
13 
The Solar Resource 
Figure 2-5 The sun changes position depending on the time of year.
14 The Solar Resource 
Figure 2-6 Harnessing renewable energy to meet our energy needs cleanly. 
Figure 2-7 Solar energy being harnessed directly on the roofs of the eco-cabins at the Centre for Alternative 
Technology, U.K.
Fossil fuels 
You probably never thought that you would hear 
an environmentalist saying that fossil fuels are a 
form of solar energy—well think again! Fossil 
fuels are in fact produced from the clean energy of 
the sun—at the end of the day, all they are is 
compressed plant matter which over millions of 
years has turned into oil, gas, and coal—and herein 
lies the problem. It took millions of years for these 
to form, and they are soon exhausted if we burn 
them at their present rate. So yes, they are a result 
of solar energy, but we must use them with care! 
As we have seen, there are many ways in which 
we can harness solar power. Figure 2-6 shows 
some clean renewable ways in which we can 
capture solar energy not only from solar panels, 
but also from the power in the wind. Although not 
immediately apparent, the black pipeline that runs 
through the picture is in fact a small-scale hydro 
installation—yet another instance of solar energy 
being harnessed (indirectly). 
This book focuses solely on “directly” capturing 
solar energy. In Figure 2-7 we can see a variety of 
technologies being used to capture solar energy 
directly in a domestic setting. 
15 
The Solar Resource
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Positioning Your Solar Devices 
Chapter 3 
It is important to note that the position of the sun 
in the sky changes from hour to hour, day to day, 
and year by year. While this might be interesting, 
it is not very helpful to us as prospective solar energy 
users, as it presents us with a bit of a dilemma— 
where exactly do we point our solar device? 
The ancients attributed the movement of the ball 
of fire in the sky to all sorts of phenomena, and 
various gods and deities. However, we now know 
that the movement of the sun through the sky is as 
a result of the orbital motion of the earth, not as a 
result of flaming chariots being driven through the 
sky on a daily basis! 
In this chapter, we are going to get to grips with 
a couple of concepts—that the position of the sun 
changes relative to the time of the day, and also, that 
that position is further influenced by the time of 
the year. 
How the position of the 
sun changes over the day 
The ancients were aware of the fact that the sun’s 
position changed depending on the time of the day. 
It has been speculated that ancient monuments 
such as Stonehenge were built to align with the 
position of the sun at certain times of the year. 
The position of the sun is a reliable way to help 
us tell the time. The Egyptians knew this, the three 
Cleopatra’s needles sited in London, Paris, and 
New York were originally from the Egyptian city 
of “Heliopolis” written in Greek as ..í.. pó.... 
The name of the city effectively meant “town 
of the sun” and was the place of sun-worship. 
It sounds like the destination for a pilgrimage for 
solar junkies worldwide! 
We can be fairly sure that the obelisks that they 
erected, such as London’s Cleopatra’s needle 
(Figure 3-1), were used as some sort of device that 
indicated a time of day based on the position of 
the sun. 
If you dig a stick into the ground, you will see 
that as the sun moves through the sky, so the 
shadow will change (Figure 3-2). In the morning 
the shadow will be long and thin; however, toward 
the middle of the day, the position of the shadow 
not only changes, but the shadow shortens. Then 
at the end of the day, the shadow again becomes 
long. 
Of course, this effect is caused by the earth spinning 
on its axis, which causes the position of the 
sun in the sky to change relative to our position on 
the ground. 
We will use this phenomena to great effect later 
in our “sun-powered clock.” 
How the position of the 
sun changes over the 
year 
The next concept is a little harder to understand. 
The earth is slightly tilted on its axis; as the earth 
rotates about the sun on its 3651/4-day cycle, different 
parts of the earth will be exposed to the sun for 
a longer or shorter period. This is why our days are 
short in the winter and long in the summer. 
17 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
18 Positioning Your Solar Devices 
Figure 3-1 Cleopatra’s needle—an early solar clock? 
Figure 3-2 How shadows change with the time of day.
The season in the northern hemisphere will be 
exactly the opposite to that in the southern hemisphere 
at any one time. 
We can see in Figure 3-3 that because of this tilt, 
at certain times of year, depending on your latitude 
you will receive more or less sunlight per day. Also 
if you look at your latitude relative to the sun, you 
can see that as the earth rotates your angle to the 
sun will be different at any given time of day, 
depending on the season. 
We can see in Figure 3-4 an example house in 
the southern hemisphere—here we can see that the 
sun shines from the north rather than the south . . . 
obviously if your house is in the northern hemisphere, 
the sun will be in the south! 
This graphically demonstrates how the sun’s 
path in the sky changes relative to your plot at 
different times of year, as well as illustrating how 
our rules for solar positioning are radically different 
depending on what hemisphere we are in. 
What does this mean for us in practice? 
Essentially, it means that we need to change the 
position of our solar devices if we are to harness 
the most solar energy all year round. 
19 
Positioning Your Solar Devices 
Figure 3-3 How the earth’s position affects the seasons. 
Figure 3-4 Seasonal variation of the sun’s position.
20 Project 1: Build a Solar-Powered Clock! 
You will need 
. Photocopy of Figure 3-5 
. Matchstick 
. Glue 
Tools 
. Scissors 
This is a dead-easy and quick sundial for you to 
build. Take a photocopy of Figure 3-5. If you want 
Project 1: Build a Solar-Powered Clock! 
Figure 3-5 Template for our “solar-powered clock.”
21 
to be really flashy you can stick it to a piece of cardboard 
in order to make it more rigid and durable. 
You need to cut out the dial that relates to the 
hemisphere that you are in—north or south. Then, 
you need to think about your latitude in degrees 
north or south. You will need to fold the sidepieces at 
the same angle marked in degrees as your latitude. 
Stick a matchstick through the point at which all 
of the lines cross. What you should be left with is 
a piece of cardboard which makes an angle to the 
horizontal. 
Now take your sundial outside and point the 
matchstick in the direction of due north (or south). 
You should be able to read the time off of the 
dial—compare this to the time on an accurate 
watch—remember you might have to add or take 
away an hour! 
Rules for solar positioning 
It is an artist’s rule that you look more than you 
paint—for solar positioning this is also true. You 
need to look carefully and make observations in 
order to understand your site. Look at how objects 
on your plots cast shadows. See where your house 
overshadows and where it doesn’t at various times 
of the year—remember seasonal variation—the 
position of the sun changes with the seasons and 
won’t stay the same all year round (Figure 3-6). 
Also, just because an area is shaded in one 
season, doesn’t necessarily mean that it is shaded 
in all seasons. In fact, this can often be used to 
Project 1: Build a Solar-Powered Clock! 
Figure 3-6 How seasonal variation affects the optimal position of solar collectors. 
Online resources 
Sundials are absolutely fascinating, and a cheap 
way to investigate the properties of the sun. The 
dial presented here is just one type of sundial; 
however, there is a lot more information out there, 
a lot more to explore—here are some links, some 
of them with printable plans that allow you to 
make different types of sundial that you might 
like to investigate! 
www.nmm.ac.uk/server/show/ 
conWebDoc.353 
www.liverpoolmuseums.org.uk/nof/sun/# 
plus.maths.org/issue11/features/sundials/ 
www.hps.cam.ac.uk/starry/sundials.html 
www.sundials.co.uk/projects.htm 
www.digitalsundial.com/product.html 
This page is well worth checking out . . . very 
ingenious this is a “digital sundial,” yes you 
read correctly—a digital sundial.
22 
your advantage. For example, in summer, you 
don’t want too much solar gain in your house as it 
might overheat; however, in winter that extra solar 
energy might be advantageous! 
Think carefully about trees—if they are deciduous, 
they will be covered with a heavy veil of leaves in 
the summer; however, they will be bare in the winter. 
Trees can be used a bit like your own automatic 
sunshade—in summer their covering of leaves blocks 
the sun; however, in the winter when they are bare 
they block less sun. 
Make a record of your observations—drawings 
are great to refer back to. Keep a notebook where 
you can write any interesting information about 
what areas are and aren’t in shadow. Note anything 
interesting, and the time of day and date. 
Make sure that you are on the lookout on the 
longest and shortest days of the year—the first day 
of summer and the first day of winter. This is 
because they represent the extremes of what your 
solar observations will be; therefore, they are 
particularly useful to you! 
Think about when in the day you will be using 
your solar device. Is it a photovoltaic cell that you 
would like to be using for charging batteries all 
day. Or, is it a solar cooker that you will be using 
in the afternoon? Think about when you want to 
use it, and what sunlight is available in what areas 
of your plot. 
Work out which direction is north—try and find 
“true north” not just magnetic north. A compass will 
veer toward magnetic north so you need to find a 
way of compensating for this. Having a knowledge 
of where north and south is can be essential when 
positioning solar devices. Note which walls face 
which cardinal directions (compass points). If you 
are in the northern hemisphere, site elements where 
coolness is required to the north, and elements where 
heat is required to the south. 
Think about the qualities of morning sun and 
evening sun. Position elements that require cool 
morning sun to the east—and those elements which 
require the hot afternoon sun to the west. 
You will need 
For the cardboard heliodon 
. Three rigid sheets of corrugated cardboard, 
2 ft × 2 ft (60 cm × 60 cm) 
. Packing tape 
. Split leg paper fastener 
For the wooden heliodon 
. Three sheets of 1/2 in. (12 mm) MDF or plywood 
2 ft × 2 ft (60 cm × 60 cm) 
. Length of piano hinge 2 ft (60 cm) 
. Countersunk screws to suit hinge 
. Lazy Susan swivel bearing 
For both heliodons, you will need 
. Clip on spotlamp 
. Length of dowel 
. Large blob of plasticine/modeling clay 
Tools 
For the cardboard heliodon 
. Scissors 
Project 2: Build Your Own Heliodon 
Project 2: Build Your Own Heliodon
23 
. Craft knife 
. Protractor 
For the wooden heliodon 
. Bandsaw 
. Pillar drill 
. Sander 
. Protractor 
We have already seen in this chapter about the 
sun’s path—and we have learnt how we can use 
the sun to provide natural lighting and heating. 
We saw in Figure 3-3 how the position of the sun 
and the earth influences the seasons, and how the 
path of the sun in the sky changes with the seasons. 
This is important to us if we want to design optimal 
solar configurations, as in order to maximize solar 
gain, we need to know where the sun is shining! 
A heliodon is a device that allows us to look at 
the interaction of the light coming from the sun, 
and any point on the earth’s surface. It allows us to 
easily model the angle at which the light from the 
sun will hit a building, and hence see the angle 
cast by shadows, and gauge the paths of light into 
the building. 
The heliodon is a very useful tool to give us a 
quick reckoning as to the direction of light coming 
into the room, and what surfaces in that room will be 
illuminated at that time and date with that orientation. 
A heliodon is also very useful for looking at 
overshadowing—seeing if objects will be “in the 
way” of the sun. 
With our heliodon, it is possible to construct 
scale models that allow us to see, for example, if a 
certain tree will overshadow our solar panels. The 
heliodon is therefore a very useful tool for solar 
design, without having to perform calculations. 
In this project, we present two separate designs. 
The first is for a cardboard heliodon, which is 
simple if you just wish to experiment a little with 
how the heliodon works. The design requires few 
materials and only a pair of scissors—but, it may 
wear out over time. This does not mean that there 
is any reason for it to be less rigid than its sturdier 
wooden equivalent. The second design is for a 
more rigid permanent fixture which can be used 
professionally, for example if you are a professional 
who will routinely be performing architectural 
design or using the heliodon for education. 
Our heliodon will consist of three pieces of board. 
The first forms a base; on top of this base, we affix 
a second board which is allowed to swivel by way 
of, in the wooden version, a “Lazy Susan” bearing. 
This is a ball-bearing race that you can buy from a 
hardware shop, which is ordinarily used as a table 
for a “Lazy Susan” rotating tray. 
In the cardboard version, we simply use a split 
leg pin pushed through the center of both sheets, 
with the legs splayed and taped down. 
The third board is hinged so that the angle it 
makes with the horizontal can be controlled, it is 
also equipped with a stay to allow it to be set at the 
angle permanently and rigidly. And that is just 
about it! With the wooden version, a length of 
piano hinge accomplishes this job admirably, and 
with the cardboard version, a simple hinge can be 
made using some strong tape. 
The other part of the heliodon is an adjustable 
light source. This can be made in a number of 
ways. The simplest of which is a small spotlamp 
equipped with a clip that allows it to be clamped to 
a vertical object such as the edge of a door. Slide 
projectors are very good at providing a parallel 
light source—these present another option if their 
height can easily be adjusted. If you will be using 
the heliodon a lot, it would make sense to get a 
length of wood mounted vertically to a base, with 
the dimensions given in Table 3-1 marked 
permanently on the wood. 
Heliodon experiments 
Once you have constructed your heliodon you can 
begin to perform some experiments using it. 
Project 2: Build Your Own Heliodon
24
You need to be aware of the three main 
adjustments that can be made on the heliodon. 
. Seasonal adjustment—by moving the lamp up and 
down using the measurements listed above, it is 
possible to simulate the time of year. 
. Latitude adjustment—by setting the angle that the 
uppermost flat sheet makes with the base, you can 
adjust the heliodon for the latitude of your site. 
. Time of day adjustment—by rotating the assembly, 
you can simulate the earth’s rotation on its axis, 
and simulate different times of day. 
The two table adjustments are illustrated in 
Figure 3-7. 
In order to secure the table at an angle, probably 
the easiest way is to use a length of dowel rod with 
a couple of big lumps of modeling clay at each 
end. Set the angle of the table to the horizontal, 
then use the dowel as a prop with the plasticine to 
secure and prevent movement. 
There are a couple of simple experiments that 
we can do with our heliodon to get you started. 
Remember the sundial that you made earlier in the 
book? Well, set the angle of latitude on your table 
to the angle that you constructed your sundial for 
(Figure 3-8). You will see that as you rotate the 
table, the time on the sundial changes. You can use 
this approach to calibrate your heliodon. You might 
like to make some marks on the cardboard surface 
to indicate different times of day. 
The next stage of experimentation with the 
heliodon is to look at modeling a real building. 
Project 2: Build Your Own Heliodon 
Compass points 
Remember to think carefully about where north 
and south are in relation to your modeling table. 
Consider whether the site you are modeling is in 
the north or south hemisphere and adjust the 
position of your model accordingly. 
Figure 3-8 Heliodon sundial experiment. 
Figure 3-7 Heliodon table adjustments. 
Table 3-1 
Lamp heights for different months of the year 
January 21 8 in. 20 cm from floor 
February 21 22 in. 55 cm from floor 
March 21 40 in. 100 cm from floor 
April 21 58 in. 145 cm from floor 
May 21 72 in. 195 cm from floor 
June 21 80 in. 200 cm from floor 
July 21 72 in. 195 cm from floor 
August 21 58 in. 145 cm from floor 
September 21 40 in. 100 cm from floor 
October 21 22 in. 55 cm from floor 
November 21 8 in. 20 cm from floor 
December 21 2 in. 5 cm from floor 
These measurements are assuming a measurement of 87 in. between 
the center of the heliodon table and the light source
25 
Project 3: Experimenting with Light Rays and Power 
Construct a model from cardboard (Figure 3-9), 
and include for example, window openings, doors, 
patio doors, and skylights. By turning the table 
through a revolution, it is possible to see where 
the sun is penetrating the building, and what parts 
of the room it is shining on. This is useful, as it 
allows us to position elements of thermal mass in 
the positions where they will receive the most solar 
radiation. 
We can also make models of say, a solar array, 
and cluster of trees, and see how the trees might 
overshadow the solar array at certain times during 
the year. Use the heliodon with scale models to 
devise your own solar experiments! 
Now with modern computer aided design (CAD) 
technology, the heliodon can be replicated digitally 
inside a computer. Architects routinely use pieces 
of CAD software to look at how light will 
penetrate their buildings, or whether obstructions 
will overshadow their solar collectors. However, 
heliodons are still a very quick, simple technology 
which can be used to make a quick appraisal of 
solar factors on a model building. A professional, 
more durable heliodon can be seen in Figure 3-10. 
You will need 
. Small torch 
. Length of string 
. Tape 
. Big sheet of paper 
. Bunch of pencils 
. Elastic band 
Attach the large sheet of paper to the wall using 
the tape. Then, take the piece of string, and attach 
one end roughly to the center of the paper with the 
tape. Now hold the string to one side of the piece 
of paper, and attach the torch to the string so that 
the bulb of the torch falls within the boundary of 
the paper. 
We are going to see how angle affects the light 
power falling on a surface when the distance from 
the surface remains the same. 
Now imagine our torch as the sun, hold the 
torch to face the paper directly keeping the string 
taught. You should see a “spot” of light on the paper. 
Online resources 
Read more about heliodons on the web 
www.pge.com/003_save_energy/ 
003c_edu_train/pec/toolbox/arch/heliodon/ 
heliodon.shtml 
arch.ced.berkeley.edu/resources/bldgsci/ 
bsl/heliodon.html 
en.wikipedia.org/wiki/Heliodon 
Figure 3-9 Using a cardboard model building to 
model solar shading. 
Project 3: Experimenting with Light Rays and Power
26 
Draw a ring around the area of highest light intensity. 
Now, hold the torch at an angle to the paper, and 
again with the string taught, draw a ring around the 
area of high intensity. Repeat this at both sides of 
center a few times at different angles. 
Figure 3-11 shows us what your sheet of paper 
might look like. 
What can we learn from this? Well, the power of 
our torch remained the same, the bulb and batteries 
were the same throughout the experiment, the amount 
of light coming out of the torch did not change. 
However, the area on which the light fell did 
change. When the torch was held perpendicular 
to the paper, there was a circle in the middle of 
the page. However, hold the torch at an angle to 
the page and the circle turns into an oval—with the 
result that the area increases. What does this mean 
to us as budding solar energy scientists? Well, the 
sun gives out a fixed amount of light; however, as 
it moves through the sky, the plane of our solar 
collectors changes in relation to the position of the 
sun. When the sun is directly overhead of a flat 
plate, the plate receives maximum energy; however, 
as we tilt the plate away from facing the sun directly, 
the solar energy reaching the plate decreases. 
You might have noticed that as you angled the 
torch and the beam spread out more, the beam also 
became dimmer. 
Remember the bunch of pencils? Well grab them 
and put an elastic band around them. Imagine each 
pencil is a ray of light from the sun. Point them 
down and make a mark with the leads on a piece 
of paper. Now, carefully tilt all the pencils in relation 
to the paper and make another mark with 
all the pencils at the same time (Figure 3-12). 
As you can see, the marks are more spread out. 
Remembering that we are equating our pencil 
marks with “solar rays,” we can see that when a 
given beam of light hits a flat surface, if the beam 
hits at an oblique angle, the “rays” are more spread 
out. This means that the power of the beam is 
being spread out over a larger area. 
It is important that we understand how to make 
the most of the solar resource in order to make our 
solar devices as efficient as possible. 
Project 3: Experimenting with Light Rays and Power 
Figure 3-11 Light ray patterns drawn on paper. Figure 3-12 Bunch of pencils experiment. 
Figure 3-10 A professional architect using a heliodon 
to make estimations of solar gain on a model building.
Solar Heating 
Chapter 4 
The sun provides us with heat and light that is 
essential to life all year round. 
One of the most efficient ways of harnessing the 
sun’s energy is to use it to space heat our buildings, 
and produce hot water for our daily needs, 
such as washing, cleaning, and cooking. 
When you think about the truly tremendous 
amount of heat that the sun produces, it seems 
absolutely ridiculous that we should want to burn 
our precious fossil fuels to heat things up. 
We can use the sun to directly heat our buildings— 
this is known as passive heating—or we can use an 
intermediate storage and distribution medium such 
as water or air. The advantage of using water or air 
as a storage medium for the heat, is that we can 
concentrate the sun, and collect it efficiently using 
solar collectors, and then using a distribution network 
of pipes or ducts, we can direct the heat to where 
we want it; and, more importantly, direct the heat to 
the places where it can be utilized most effectively. 
In this chapter, we are going to be looking at the 
fundamentals of a solar hot water heating system. 
By the end of the chapter, you should have an 
understanding of how such systems work, and be 
armed with the knowledge to begin researching 
and installing your own hot water system. 
Why use solar energy 
for heating? 
There are considerable environmental benefits 
associated with using renewable energy for heating. 
Consumption of fossil fuels for heating is tremendous 
when you consider the global scale. Producing as 
much as possible of our heat from renewable 
resources will considerably reduce our consumption 
of fossil fuels. 
Can I use my roof 
to mount my solar 
heating panels? 
The roof seems an obvious place to want to mount 
your solar heating panels. After all, you have a large 
area which is currently unutilized just waiting for 
some clean green energy generation! 
First of all, you should consider the structural 
integrity of your roof and how strong it is. 
Remember, the roof will not only need to support 
the weight of the solar heating panel and all of the 
associated paraphernalia, but might also need to 
support your weight as you install it. 
You will also need to consider the orientation 
of your roof and whether it is positioned in such 
a manner that it will receive optimal solar gain. 
If you are in the northern hemisphere, you will 
want a roof which faces as near to due south as 
possible. If your roof does not face directly due 
south, there will be some loss of efficiency—which 
is proportional to the angle of deviation from due 
south. 
If you live in the southern hemisphere, the 
reverse is true—you want a roof that faces due 
north in order to catch the best of the sun’s rays. 
27 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
How does solar 
heating work? 
On a hot summer day, if you are walking around a 
parking lot, gently touch a black car, and the chances 
are it will feel very hot. Now touch a silver or white 
car, and you will find that it is significantly cooler. 
This is the principle that underpins solar heating. 
A black surface heats up quickly in the sun. 
Our demand for hot water is driven by a number 
of things. We use hot water every day for tasks such 
as washing our hands, clothes and dishes. From now 
on, we will refer to this as “solar hot water.” We can 
also use hot water for heating our homes. We will 
refer to this as “solar space heating” from now on. 
What we need to do, is look at our demand for 
heated water, and see how it correlates to the 
energy available from the sun. 
Solar hot water 
Our demand for hot water is fairly constant 
throughout the year. We use more or less the same 
amount of hot water for washing and cleaning in 
the winter as we do in the summer. 
Solar space heating 
We can also use solar energy to heat our space 
directly—passively, rather than using an active 
system. This is called passive solar design. We can 
design our buildings with large expanses of glass 
on the sun-facing façades in order to capture the 
solar energy and keep the building warm and light. 
However, the requirements for space heating are 
different in the winter from in the summer. If we 
design our buildings for “summer conditions,” they 
could be intolerably cold in the winter. For this 
reason, we can use architectural devices such as 
shading and brie soleil to ensure that the room 
receives an optimal amount of light in both 
summer and winter. Passive solar design is a whole 
book in its own right though! 
What does a solar 
heating system 
look like? 
Figure 4-1 illustrates a basic solar water heating 
system. 
We can see a large storage tank in the Figure. 
This is filled with water and is used as a thermal 
store. It is imperative that this tank is incredibly 
well insulated as it is pointless going to a lot of 
effort to collect this solar energy if we then lose it 
in storage! 
You will notice that the solar hot water tank has 
a gradient fill—this denotes the stratification of the 
water—the colder water sinks to the bottom, while 
the warmer water is at the top of the tank. 
We draw the hot water off from the top of the 
tank, while replacing the hot water with cold water 
at the bottom of the tank. This allows us to maintain 
the “layered” stratified nature of the tank. 
At the bottom of the tank, we can see a coil; this 
is shown more clearly in Figure 4-2—this coil is in 
fact a copper pipe—we can see that the pipe enters 
the tank at the bottom, and exits the tank at the top. 
The pipes are connected in a closed circuit to a 
solar collector. This closed circuit is filled with a 
fluid which transfers the heat from the solar cell to 
the tank. 
This is the simplest type of solar system—it is 
called a thermosiphon. The reason for this name is 
that the process of circulation from the solar cell to 
the tank is driven by nothing more than heat. Natural 
convective currents set up a flow, whereby the hot 
water makes its way around the circuit. 
It is also possible to insert a pump into this circuit 
to increase the flow of the heat transfer medium. 
28 Solar Heating
We can also drive this pump using photovoltaic 
solar cells. This means that our heating is not using 
electricity from the grid—and hence not using 
energy generated from fossil fuel sources. There is 
one manufacturer, Solartwin, which supplies a 
system which consists of a solar thermal panel, and 
a pump driven by photovoltaics. The advantage of 
this approach is that the energy for the pump is 
provided at the same time as there is heat in the 
system. 
Tip 
A good science fair project might be to build a 
demonstration solar water heating system using 
easy-to-use flexible aquarium tube for the 
“plumbing” and a soda bottle for the hot water 
storage tank. A few thermocouples or thermistors 
will allow you to monitor the temperatures around 
the setup and see how effectively it is working. 
29 
Solar Heating 
Figure 4-1 A basic solar water heating system. 
Figure 4-2 A cutaway of a thermal store tank.
Solar collectors 
There are two types of solar collector: flat plate, 
and evacuated tube. We can see in Figure 4-3 
the two types of collectors compared. While a 
greater amount of sun falls on the flat plate, the 
evacuated tube collectors are better insulated. 
However, as the sun moves in an arc through the 
sky, the flat plate collector’s effective area becomes 
smaller, and as the evacuated tube collectors are 
cylindrical, the area presented toward the sun is 
the same. 
In Figure 4-4 we see the make up of a flat plate 
collector. It is essentially quite a simple device. 
There is insulation, which stops the heat that it 
absorbs from being transmitted into the roof it is 
mounted on. A coil of tube within this collects the 
heat and transmits it to the storage tank, and at the 
front of the collector is an absorbent surface. 
This could simply be matt black, or it could be a 
selective coating. 
On the roof shown in Figure 4-5 we can see a 
variety of different solar cells, both thermal and 
photovoltaic nestling together in harmony. 
30 Solar Heating 
Figure 4-3 Flat plate versus evacuated tube collectors. 
Figure 4-4 Cutaway of a flat plate collector.
31 
Project 4: Build Your Own Flat Plate Collector 
Figure 4-6 A commercially made clip fin collector. 
We are now going to make a flat plate collector. 
There are a number of different types of collector, 
all suitable for relatively simple manufacture in a 
home workshop (Figures 4-6 to 4-8). 
The key thing to remember about solar collectors 
is keeping the heat in and the cold out. This can be 
accomplished by using glazing on the sun-facing 
side of the panels and thermal insulation on the side 
Project 4: Build Your Own Flat Plate Collector 
Figure 4-5 An array of different solar thermal cells on a roof.
that faces away from the sun. We need to try to 
eliminate thermal bridges as far as we possibly can. 
Aluminum clip fins are one of the easiest ways 
of assembling a solar collector quickly, as they 
essentially clip onto a matrix of copper pipe. 
Another way of constructing a solar collector is to 
use an old radiator painted black inside an insulated 
box—crude but effective! (Figure 4-9). This system 
contains more water, and as a result has a slower 
response time. This is because it takes more time to 
heat up the thermal mass of the radiator. 
Warning 
One of the problems that solar collectors suffer 
from is freezing in the winter. When temperatures 
drop too low, the water in the pipes of the 
collectors expands—this runs the risk of severely 
damaging the collectors. 
32 Project 4: Build Your Own Flat Plate Collector 
Figure 4-7 A home-made clip fin collector. 
Figure 4-8 Aluminum clip fins.
While having a pool in your yard is a great way to 
exercise and enjoy the summer sun, swimming 
pools are notorious for “drinking” energy. 
The problem is that there is simply such a great 
volume of water to heat! 
Energy is becoming more expensive as we begin 
to realize the serious limitations of the previously 
cheap and abundant fossil fuels. 
Some people heat their pools in order to be able 
to enjoy them out of season; however, that comes 
with a big associated energy cost. 
Before you even start to consider heating your 
pool using solar energy, you need to consider 
energy reduction and efficiency measures. You 
might want to consider your usage patterns. Will it 
really make much difference to me if I can’t use 
my pool out of season? After all, who really wants 
to swim when it is cold and wet outside! Also you 
might want to consider energy minimization 
strategies. Is your pool outside and uncovered at 
the moment? Heat rises . . . so all that heat that you 
are throwing into your pool is being lost as it 
dissipates into the atmosphere. This isn’t smart! 
Building some kind of enclosure over your pool 
will make the most of any investment that you put 
into solar heating your pool. 
Once you have taken steps to minimize the 
energy that your pool requires, you can begin to 
make advances toward heating it using free solar 
energy. There is nothing really too complicated 
about a solar pool heating system. As we only need 
to elevate the temperature of the water slightly, we 
can use simple unglazed reflectors. 
The reason? Well think of it like this . . . the 
water you get from the hot tap to wash with is 
significantly hotter than the sort of temperature 
you would be expecting to swim in. A domestic 
solar hot water rig heats a small volume of water 
to a very high temperature. By contrast, a solar 
pool heating system, takes a large quantity of 
water, and heats it by a small amount. Here is the 
fundamental difference. Because the water is 
33 
Project 5: Solar Heat Your Swimming Pool 
Project 5: Solar Heat Your Swimming Pool 
Figure 4-9 A recycled radiator collector.
circulating at a faster rate, unglazed collectors can 
provide acceptable efficiency. 
But that’s not all! 
In some hot climates, pools can have a tendency 
to overheat. Solar collectors can save the day here! 
By pumping water through the collectors at night it 
is possible to dump excess heat. 
This technology isn’t just applicable to small pools 
at home, large municipal pools are also heated by 
solar technology in a number of cases. Take for 
instance the International Swim Center at Santa Clara, 
California, 13,000 square meters of solar collector 
heat a total of 1.2 million gallons of water a day! 
Figure 4-10 illustrates solar pool heating. 
The Supplier’s Index (Appendix B) lists a 
number of companies that sell products for solar 
heating your pool. 
Do we need to use solar 
thermal power directly? 
If we consider power generation on a large scale, 
all of our power stations whether they be nuclear, 
coal, oil, or gas fired, all produce heat primarily, 
and then use this heat to produce steam, which 
then, through using rotating turbines, produces 
electricity. 
This means, that at present, we do not produce 
electricity directly from chemicals, like we do in a 
battery—we first produce heat as an intermediate 
process, which is in turn used to produce electricity. 
Once we recognize this, we quickly realize that 
it could be possible to use solar thermal energy to 
raise steam to generate electricity. 
And this is exactly what they are doing in 
Kramer Junction, California. 
Tip 
Enerpool is a free program that can be used to 
simulate your swimming pool being heated with 
solar collectors. By inputting information such as 
your location, and how the pool is covered. The 
program can predict what temperature your pool 
will be at, at any given time! 
www.powermat.com/enerpool.html 
34 Project 5: Solar Heat Your Swimming Pool 
Figure 4-10 Solar pool heating.
Although we have discussed basic systems 
here for producing solar heat—and by no means 
is this comprehensive coverage of solar heating 
(the subject really deserves several books in its 
own right) there are a number of things that we 
can do to improve our system. If our system is 
“active,” which is to say if there is a pump 
driving a working fluid around the system, 
then we can do a little more to control the 
fluid. 
If our system is passive, i.e., a thermosiphoning 
system, where the fluid makes its way around the 
system as a result of changes in density, then we 
might at least like some feedback as to what our 
system is doing. 
You will need 
. Negative temperature coefficient thermistor 
. 2 × 10 k resistor 
. 100 k variable resistor 
. 741 op amp 
. 1 M resistor 
. 4.7 k resistor 
. BC109 NPN transistor 
. 6 V piezo buzzer 
. Heatshrink tubing 
. Mastic/silicone sealant 
Optional 
. 6 V relay 
. Protection diode 
Tools 
. Soldering iron 
. Side cutters 
. Solder 
35 
Project 6: Useful Circuits for Solar Heating 
Project 6: Useful Circuits for Solar Heating 
Figure 4-11 Solar thermal power in the Mojave desert. Courtesy Department of Energy.
The following is a simple circuit that uses a 
thermistor as the sensing element to provide 
feedback as to the condition of a surface being 
monitored. There are two simple circuits here— 
both are similar with one small change—the 
position of the thermistor and variable resistor 
which change places (Figures 4-12 and 4-13). 
Protecting the sensor 
against the elements 
A thermistor as supplied from the components 
shop is a pretty fragile beast, and as such should 
be respected if reliable operation is wanted. 
36 Project 6: Useful Circuits for Solar Heating 
Figure 4-12 Solar heating over temperature indicator. 
Figure 4-13 Solar heating under temperature indicator.
The device is designed to be soldered onto a 
printed circuit board; however, we are expecting it 
to be used in a much more hostile environment. 
For this reason, provision should be made to 
insulate the leads of the thermistor with some 
heatshrink tubing, which will provide mechanical 
support for the soldered joint, and also prevent 
ingress of water. 
Once each individual lead has been insulated, 
the pair can be bound together with a little more 
heatshrink, or failing that a little bit of tape. The 
sensor should be provided with long enough leads 
to comfortably reach the circuit board. If your 
solar collector tracks the sun, you will need to 
ensure that the leads are sufficiently long to reach 
back to the circuit board, even at the extent of your 
collector’s movement. 
Taking this a step further, you need to mate 
your sensor to the surface being monitored. A 
little squeeze of heat transfer compound in the gap 
between thermistor and the surface is not a bad 
idea—you can get this from computer suppliers, as 
it is commonly used to ensure a good surface 
interaction between a CPU and heatsink. 
Once you have done this, you can apply silicone 
sealant liberally to hold the sensor in place. If you 
really want to go the whole hog, you can even insulate 
the other side of the sensor with a little thermal 
lagging, such as polystyrene or a slice of foam pipe 
lagging. This will prevent the sensor from being 
unduly influenced by external fluctuations in 
temperature. 
Calibrating the sensor 
When setting the circuit up, you will need to calibrate 
the sensor against a reference of known temperature. 
A water bath is a good way of providing a stable 
temperature. To get the temperature you desire, get a 
cup of ice water and a cup of boiling water, and use 
these to adjust the temperature of a cup of water with 
a thermometer immersed in it. 
Modifications to the circuit 
Although the circuit is useful in its own right, there 
are a couple of things that we can do to improve its 
functionality. As it stands, the circuit provides an 
“alert” when the temperature goes out of condition; 
however, we might consider a scenario where we 
are not at home to take action. In this instance, we 
might want to replace the piezo buzzer in the system 
with a relay and protection diode. This is a straight 
swap, and allows the circuit to then control an 
automatic device which can take action—for 
example a pump or electronic valve. 
To give you an example of how this circuit 
could be useful in your solar water heating 
system, in freezing weather, if no water is 
circulating in the pipes, there is a risk that that 
water could expand and burst your pipes. To 
overcome this, a relay could switch on a trickle 
pump which keeps a little water circulating 
through the pipes. This water will carry with it 
some heat from the thermal store, which should 
keep your pipes free of ice. 
Equally, with the resistors reversed as in the 
second circuit, you might want to set up a system 
whereby a pump is triggered when heat in the 
collector is sensed. This ensures that hot water 
isn’t pumped through a cold collector. 
What is the future 
of solar heating? 
It is inevitable that in the future, we will need to 
seek different solutions to our problems as we are 
forced not to depend on fossil fuels. Solar energy 
certainly has a place in meeting our heating needs 
in the future, and considering the energy from the 
sun is free, it is very surprising that more people 
aren’t using it now! 
We have seen in this chapter how solar heating 
can meet our heating needs, but that the availability 
37 
Project 6: Useful Circuits for Solar Heating
of solar energy is seasonal, and in part that determines 
the supply of solar hot water. 
Even when the sun cannot provide all of the 
energy all of the time, or where 100% solar 
provision would be uneconomical, it can certainly 
go a long way toward reducing the amount of energy 
we need to consume. Even pre-heating water a little 
bit in winter goes some way to saving energy. 
Another thing that needs careful consideration, 
is that if we need to provide extra energy for our 
heating needs, where will that energy come from? 
Fossil fuels pollute the atmosphere and are a finite 
resource, nuclear leaves a legacy of toxic waste, 
but maybe solar energy has another trick up its 
sleeve—biomass! 
The trees and plants that we are surrounded by 
are effectively solar batteries! They take the energy 
produced from the sun, and using a process called 
photosynthesis, use the energy to grow. All the time 
that they are growing, they are taking in carbon 
dioxide from the atmosphere and producing oxygen. 
Once a tree has grown, we can cut it down and burn 
it. While this process releases carbon dioxide into 
the atmosphere, there is no “net gain” of carbon 
dioxide, as the tree took the carbon dioxide out of 
the atmosphere while growing! 
38 The Future of Solar Heating
Solar Cooling 
Chapter 5 
In hot climates, it can often become uncomfortably 
hot—in the modern world, we tend to look toward 
air conditioning to provide a comfortable internal 
atmosphere; however, air conditioning often leaves 
us with dry stale air. 
While it would seem to be counterintuitive to 
use the sun to cool things down, there are a 
number of techniques that we can use to cool 
things down by employing the sun’s energy. 
Why air conditioning 
is bad 
The amount of energy that air conditioning consumes 
is truly tremendous. In addition to this, the heat 
extracted from the building is simply dumped out 
into the atmosphere. Air conditioning cooling 
stacks are a breeding ground for Legionella bacteria, 
and the refrigerants used in air conditioning are 
ozone-depleting and add to the burden of global 
warming. While there has been a worldwide move 
to eliminate CFCs from air conditioning units 
because of the damage they do, the interim HCFC 
and HFC chemicals are still not environmentally 
friendly. 
What can we 
do instead? 
Rather than using large amounts of fossil fuels, 
there are a number of other strategies that we can 
use to cool our buildings. 
Passive solar cooling 
There are a number of ways that we can design our 
buildings to stay at a pleasant internal temperature, 
and prevent them from overheating, even in the 
summer. 
Trombe walls 
As with many of the themes in this book, this idea 
is not a new one, in fact it was patented in 1881 
(U.S. Patent 246626). However, the idea never 
really gained much of a following until 1964, 
when the engineer Felix Trombe and architect 
Jacques Michel began to adopt the idea in their 
buildings. As such, this type of design is largely 
referred to as a “Trombe wall.” 
Figure 5-1 shows a Trombe wall on one of the 
resident’s houses at the Centre for Alternative 
Technology (CAT), U.K. 
Let’s describe the construction and operation of 
the Trombe wall. 
Essentially, the Trombe wall is a wall with a 
high thermal mass, the wall is painted black to 
enable it to absorb solar radiation effectively. 
The wall is also separated from the outer skin of 
glazing by an air gap. 
The original Trombe walls were not particularly 
effective. They worked by absorbing heat in the 
thermal mass during the day. At night, this heat 
would be dissipated both into the room—but also 
to the outside through the air gap and glazing. The 
theory was that the glazing would help to retain 
heat, and because the thermal mass had gained 
enough heat during the day, it would be warmer 
39 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
than the internal room temperature, as a result, the 
room would warm up. 
In reality it appeared that most of the heat was 
simply dumped to the cold outside. 
A series of improvements were made to the 
design of the Trombe wall which significantly 
increased its performance. In the improved version 
of the Trombe wall, there are vents at the top and 
bottom of the wall, and also on the glazing. 
These vents have a mechanism that allows them 
to be opened and closed in certain configurations. 
The general scheme of things is that the sun 
shines through the glazing, where it heats up the 
thermal mass of the wall behind. The wall, being 
of a construction that has a high thermal mass (for 
example masonry or concrete) transfers some of 
the heat energy to the air in the gap between the 
glazing and the wall as it heats up. 
A convection current is set up. If you are 
familiar with heat and the way it affects air, you 
will know that as air heats up, the molecules of 
gas gain a little more energy—this causes them 
to bounce around a bit more, and as a result, they 
tend to spread out a little bit. As they do this, the 
body of gas becomes less dense. As you will 
know if you have ever observed a spill of oil on 
a body of water, the less-dense compound floats 
to the surface as it is displaced by the more-dense 
compound. In this case, the lighter air rises up 
through the gap between the wall and the glazing. 
This is the principle that hot air balloons use to 
operate—hot less-dense air floats above denser 
air! 
This convective current can be used to either 
heat or cool the building. 
Remember those gaps in the wall and glazing— 
well, if both of the vents in the wall (the thermal 
mass side of things) are opened, air will be sucked 
out of the room at the bottom, heated as it contacts 
the thermal mass, and using convection will rise up 
to the top of the air gap, where it flows back into 
the room. 
Of course during the summer, this heat isn’t 
really wanted—so the flaps can simply be closed 
in order to keep the room cool. 
But this chapter did say it was about solar 
cooling! 
Well, if you also have flaps in the glazing which 
can be opened and closed, you can then open a 
flap at the top of the glazing, and at the bottom of 
the thermal mass. The flap at the top of the thermal 
mass is closed. 
This sets up a convective current which sucks air 
out of the bottom of the room, and heats it slightly, 
causing it to rise. But rather than this air being fed 
back into the room, the air is instead dissipated 
into the outside atmosphere. This has the effect of 
sucking air from the room. This air has to be 
replaced somehow, so what happens is that fresh 
air is sucked in through cracks in the building 
fabric, gaps in doors and windows, etc. This provides 
a fresh cooling breeze for the occupants 
(Figure 5-2). 
40 Solar Cooling 
Figure 5-1 Trombe wall at CAT, U.K.
Passive evaporative techniques 
When water evaporates, it takes with it energy. 
We can exploit this phenomenon to cool buildings. 
These techniques all require water, which might 
not be possible in some hotter countries where 
water availability is limited. Also, it must not be 
forgotten that there is a requirement for energy to 
pump the water to the top of the building. This 
energy must be provided in a sustainable manner. 
Roof sprays 
Spraying the roof with a fine mist of water is one 
way to keep the roof wet and permit evaporative 
cooling. The roof must be suitably coated to 
prevent water ingress, which could damage the 
fabric of the building. 
Roof ponds 
A roof pond is one way of providing a large body 
of water which can be evaporated, taking heat with 
it as it leaves the roof. 
Active solar cooling 
Active solar cooling is a little bit more involved 
than passive solar cooling. In active solar cooling, 
we use a thermally driven process of some sort in 
order to cool our buildings, rather than air 
conditioning which is thirsty for electricity. Of 
course, as we have seen, we can easily generate 
heat using solar methods. 
To understand how solar cooling differs from 
conventional refrigeration methods, let’s compare 
the two and look at similarities and differences. 
In a conventional refrigeration setup, 
a refrigerant—a substance that readily evaporates at 
a low temperature—is compressed, which causes it 
to become liquid. This compression is usually 
driven by an electric motor—using valuable watts 
in the process. The refrigerant is then allowed to 
expand—to do this it requires heat, which it gains 
from the material under refrigeration. As the heat 
transfers from the material to be refrigerated to the 
refrigerant, the refrigerant expands. It must then be 
compressed and forced around the loop again! This 
cycle continues indefinitely—no refrigerant should 
escape from the system. 
Our system works in a slightly different way. 
The refrigerant is kept “locked up” in a material 
which soaks up refrigerant like a sponge soaks up 
water. As we heat this material, the refrigerant is 
liberated from it, turning into a liquid as it condenses. 
This liquid will readily evaporate again—it 
is encouraged to do this by the absorbent material 
which tries to “suck” the refrigerant back once it 
has cooled. As the refrigerant shuttles back to the 
absorbent material it takes heat with it. This shuttling 
back and forth continues—so the process 
is a bit more like a train going back and forth in 
a straight line, than a train continually circling in 
a loop. 
41 
Solar Cooling 
Figure 5-2 Trombe wall modes of operation.
I am grateful to Jaroslav Vanek, Mark “Moth” Green 
and Steven Vanek for the information on how to make 
a solar-powered ice-maker. This design was originally 
published in Home Power magazine, Issue no. 53. 
You will need 
. Four sheets galvanized metal, 26 ga. 
. 3 in. black iron pipe, 21 ft length 
. 120 sq ft mirror plastic 
. 21/4 in. stainless steel valves 
. Evaporator/tank (4 in. pipe) 
. Freezer box (free if scavenged) 
. 4 ft × 8 ft sheet 3/4 in. plywood 
. six 2 × 4 timbers, 10 ft long 
. Miscellaneous 1/4 in. plumbing 
. Two 3 in. caps 
. 11/4 in. black iron pipe, 21 ft length 
. Four 78 in. long 11/2 in. angle iron supports 
. 15 lb ammonia 
. 10 lb calcium chloride 
This design is for an ice-maker which will produce 
about 10 lb of ice in a single cycle. It uses the 
evaporation and condensation of ammonia as a 
refrigerant. If you remember in the explanation 
above, I mentioned that we needed a refrigerant 
and an absorber for this type of cooler to work. 
Well, the ammonia is our refrigerant, and we use a 
salt—calcium chloride—as the absorber. You 
might have seen small gas fridges often used in 
caravans and RVs which can be powered by 
propane—these also generally use ammonia as a 
refrigerant—however, they tend to use water as the 
absorbing medium. 
Construction and assembly 
The first item to be assembled is the solar collector 
pipe. This is made from the length of black iron 
pipe. First of all you should cut a foot off the end, 
as we will need this for the ammonia storage tank. 
The pipe should be capped at the ends with the 
3 in. black caps, but before you do this, you need 
to drill one of the caps to accept a 1/4 in. nipple and 
a coupling for the rest of the plumbing. The collector 
can now be filled with the calcium chloride salt 
which will act as the absorber. The caps can now be 
secured firmly in place. Whatever method you 
choose, you should ensure that the joint is capable 
of withstanding pressure—as when the ammonia is 
produced it will be hot and anywhere near two 
hundred pounds per square inch pressure. 
You next need to form a condenser coil and tank. 
The tank is easy—take a standard 55 gallon drum, 
and slice it in half. This will give you a nice 
container to pump full of water. 
Now a word about gravity—there are no pumps 
in this system to make the working fluid go up 
and down, so you need to think of other ways of 
doing this. Mount the condenser coil high up, 
above the level of the solar collector. Now have 
the pipe from the collector running to the top of 
the coil in the tank. The pipe from the bottom 
of the coil to the storage tank should be as straight 
a run downhill as possible, try to eliminate any 
bends or kinks if at all possible (Figures 5-3 
and 5-4). 
In the collector made by Jaroslav Vanek, Mark 
“Moth” Green and Steven Vanek, the steel pipe of 
the collector was supported from the ground by 
two sturdy uprights. The solar collector was then 
The original article can be downloaded from the 
Home Power website at: 
homepower.com/files/solarice.pdf 
42 Project 7: Solar-Powered Ice-Maker 
Project 7: Solar-Powered Ice-Maker
suspended from this using U bolts. This allowed 
the collector to be moved to accommodate seasonal 
variations. 
How does the ice-maker work? 
The ice-maker works on a cycle—during the 
daytime ammonia is evaporated from the pipe at 
the focal point of the parabolic mirrors. This is 
because the sun shines on the collector which is 
painted black to absorb the solar energy—this 
collector heats up, driving the ammonia from the 
salt inside. 
At night, the salt cools and absorbs the 
ammonia, as it does this, it sucks it back through 
the collector. As it evaporates from the storage 
vessel, it takes heat with it. 
Warning 
For the system to operate for long periods of 
time, the materials used should be resistant to 
corrosion by ammonia. Steel and stainless steel 
are ideal in this respect as both are immune to 
corrosion by ammonia. Another consideration is 
the pressure under which the system will have to 
operate. 
43 
Project 7: Solar-Powered Ice-Maker 
Figure 5-3 Solar cooler layout. 
Figure 5-4 Solar cooler plumbing details.
Figure 5-5 illustrates this cycle. 
Useful addresses 
The following addresses may be useful if you wish to 
make further enquiries about this design of ice-maker: 
S.T.E.V.E.N. Foundation, 
414 Triphammer Rd. 
Ithaca, 
NY 14850 
U.S.A. 
SIFAT, 
Route 1, Box D-14 
Lineville, 
AL 36266 
U.S.A. 
Note 
This design has a number of strengths which 
make it robust and reliable in operation. One of 
those strengths is that the design has an absolute 
minimum of moving parts. The only things that 
actively move are the valves—and even these are 
operated infrequently. The elimination of moving 
parts makes this design very efficient. 
44 
Figure 5-5 The solar cooler cycle. 
Project 7: Solar-Powered Ice-Maker
Solar Cooking 
Chapter 6 
Why cook using 
the sun? 
Solar cooking is a great alternative to conventional 
cooking—rather than burning fuel and 
producing carbon dioxide emissions, or using 
precious electricity, solar cooking harnesses 
the natural energy available from the sun! It 
is a great social activity on a sunny day—barbeques 
are just sooooo yesterday—solar cooking 
is where it is at! No fumbling with matches 
and firelighters, no choking on smoke, no 
burnt sausages! Just hope that the clouds don’t 
come! 
Although you won’t see any T.V. chefs preparing 
meals on a solar cooker, it doesn’t mean that they 
aren’t any good—it just means that T.V. chefs lack 
technological imagination. 
There are lots of different designs of solar 
cooker all suited to different applications—all rely 
on similar principles—concentrating the sun’s 
energy into a small area and then trying to retain 
the heat. 
Solar cooking solutions are elegant in their 
simplicity and as such are suited to developing 
world applications (Figure 6-1). Many countries do 
not have the developed infrastructure that we have 
in the West for distributing energy. As a result, a 
hot, cooked meal is hard to come by—as fuel may 
be scarce. 
Think of it like this—the developed world is 
already using a massive amount of energy to cook 
food—with large nations like India and China 
growing and developing, our energy will run out 
sooner rather than later if everybody wants to live 
a western lifestyle—but why even should we in the 
West want to live a western lifestyle when things 
like solar cooking can be so much fun—and 
achieve the same ends that conventional cooking 
does, heating a food product. 
All of the projects in this chapter can be built 
very cheaply and are ideal for a fun summer’s 
day! 
At the end of this chapter, I have put together a 
collection of links to various different types of 
solar cooker plans that are out there on the web— 
all have different strengths and weaknesses and 
are suited to different applications, from designs 
that will just about cook a frankfurter, to large 
cookers that can be used for community catering! 
45 
Figure 6-1 A solar cooker being used in the 
developing world. Image courtesy Tom Sponheim. 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
You will need 
. Small photovoltaic cell 
. Solar motor 
. Plywood 
. Framing 
. Screws 
. Flexible acrylic mirror 
. Elastic band and pulley wheel 
or 
. Small plastic worm gear and large plastic 
gear to match 
Tools 
. Bandsaw 
. Drill 
. Router 
First of all we need to construct the parabolic 
mirror. The parabolic mirror collects all of the 
solar energy and focuses it onto our hot dog. You 
can read more about this effect in the chapter on 
Solar Collectors (Chapter 8). 
Have you ever tried bending a glass mirror? 
It doesn’t work, the least you will end up with is 
seven years bad luck, and at worse you could end 
up with bloody hands. 
Here we have a couple of options, the “qualitybuilt-
to-last” option, and the “cheapskate” option. 
The quality-built-to-last option involves buying 
some flexible acrylic mirror from the internet. This 
is often seen on auction sites in large panels as 
people use it for interior design, and can sometimes 
be found in garden supply stores as people put it at 
strategic locations in their garden in order for it to 
appear bigger. 
The acrylic mirror can be bent gently without fear 
of breaking, and also has the advantage that it can be 
drilled relatively easily without fear of splintering. 
If you are opting for the cheap option, you can 
get away with using some corrugated cardboard, 
covered in glue, followed by tin foil. Note that your 
collector efficiency will not be as good, as the surface 
is not as reflective. However, for a demonstration 
it works to a degree. 
Next, you need to construct a support for the 
mirror—if you are building to last then use 
plywood and framing. A router might be useful to 
machine a groove which will support the mirror, 
if you are making the cheaper cardboard version, you 
just need to cut some flaps to support the “mirror.” 
Now we come to the drive mechanism. We have 
a couple of options here (Figures 6-2 and 6-3). You 
can just provide a simple support for a skewer and 
turn your hot dog by hand. 
Alternatively, if you are feeling really adventurous, 
you can construct a solar motor, which will turn the 
skewer of your hot dog automatically! 
You will need 
. 1381 IC 
. 2N3904 transistor 
. 2N3906 transistor 
. 3300 µF capacitor 
. 2.2 k resistor 
This list of components is for the deluxe 
version—the automatic hot dog turner is a cool 
novelty, but not essential as it is just as easy to 
turn by hand! If you want to make a simpler 
cheaper version, substitute the plywood for card, 
the plastic mirror for tin foil, and rather than have 
a motor turn your hot dog on a skewer, just 
provide support for the skewer and do it by hand! 
46 Project 8: Build a Solar Hot Dog Cooker 
Project 8: Build a Solar Hot Dog Cooker
. Solar cell 
. High efficiency motor 
The circuit for the solar motor is shown in 
Figure 6-4, it is a simple circuit, and can easily be 
assembled on stripboard. Once you have constructed 
the solar motor driver circuit, you are going to need 
to mechanically couple the motor to the skewer. You 
may find if your motor is powerful enough, that you 
can directly drive the skewer—it would be worth 
investigating bearings to ensure that your skewer 
turns as freely as possible with a minimum of 
resistance. If you find your motor struggles to turn 
the skewer, then use a “worm drive” to reduce the 
speed of the motor—while increasing torque. 
Online resources 
Solar hot dog cookers on the web: 
www.motherearthnews.com/Green_Home_ 
Building/1978_March_April/Mother_s_Solar_ 
Powered_Hot_Dog_Cooker 
www.pitsco.com/the_cause/cause3inv.htm 
www.energyquest.ca.gov/projects/solardogs.html 
sci-toys.com/scitoys/scitoys/light/solar_ 
hotdog_cooker.html 
www.reachoutmichigan.org/funexperiments/ 
agesubject/lessons/energy/solardogs.html 
47 
Project 8: Build a Solar Hot Dog Cooker Figure 6-2 Solar hot dog cooker. 
Figure 6-3 Drive mechanism.
You will need 
. Marshmallows 
. Large Fresnel lens 
. Tin foil 
. Skewers or a toasting fork 
In this project, we are going to collect the sun’s 
energy from a large area, and focus it to a point in 
order to create localized heating. 
One way of collecting the sun’s energy from a 
large area is to use mirrors. We have already 
explored this in the “solar hot dog cooker.” You 
will read more about concentrating solar energy in 
the chapter on Solar Collectors (Chapter 8). 
In order to perform this experiment, we are 
going to need a Fresnel lens—again see the chapter 
on Solar Collectors for an explanation on how 
these work. 
Put the marshmallow on a skewer, and rest it on 
the sheet of tin foil. We are going to use the Fresnel 
lens, to focus the sun’s rays onto the marshmallow. 
When you look out of your window, there is no 
magnification or reduction of the image—the glass 
does not act like a lens; however, you will notice 
when looking through the Fresnel lens (not at the 
sun!) the image appears much bigger and magnified. 
Why is this? If you look closely, you will see 
a series of concentric circles in the Fresnel lens. 
Now think of a magnifying glass—it is round and 
circular, and “bulges” in the middle. If we look at 
the glass from side-on, we can see that both sides 
of the lens are curved—but there is also a lot of 
glass in the middle! A Fresnel lens “removes” some 
of the glass from the middle, and flattens the lens 
onto a sheet. Each little concentric ring that you see 
on the flat Fresnel sheet, is a section of lens curve. 
Look at where the sun is in the sky, and hold 
the Fresnel lens perpendicular to an imaginary line 
between the sun and your marshmallow. Move the 
lens to and fro along this line, and observe how the 
focused beam of solar energy changes on your 
marshmallow. After a little bit of time, focusing the 
sun onto the marshmallow, you should see the 
candy begin to toast! No fire required—just the 
power of the sun! 
Online resources 
Marshmallow melting web pages! 
worldwatts.com/marshmallows/solar_roaster.html 
www.altenergyhobbystore.com/marshmallow% 
20roaster.htm 
bellnetweb.brc.tamus.edu/res_grid/cuecee05.htm 
48 Project 9: Build a Solar Marshmallow Melter 
Figure 6-4 Solar motor circuit. 
Project 9: Build a Solar Marshmallow Melter
You will need 
. Eggs! 
. Drop of oil 
. Hot sunny day 
Tools 
. Black tarmac driveway 
. Frying pan 
Sometimes, on a hot sunny day, the black tarmac 
can almost seem painful to walk on barefoot as 
it is so hot. If you keep moving, your feet feel 
fine; however, if you stand in the same place for 
the same time, your feet feel very uncomfortable. 
This is because the tarmac road surface has the 
ability to act as a thermal mass and store heat. If 
you were to stand on say a flimsy piece of black 
card that had been left in the sun, it would feel 
warm to the touch; however, you would find that 
as soon as you stood on it, the heat would be 
quickly dissipated—the card doesn’t have the ability 
to store the heat. So, if we want to cook an egg 
on a sunny day . . . 
Take a peek at Figure 6-5 for the ridiculously 
simple method. 
Take a frying pan, put it on a black tarmac surface 
on a hot sunny day, put a drop of oil in the 
pan and cover the frying pan for a while with a 
sheet of glass. The pan is black, the tarmac is black 
and so will have absorbed the sun’s energy. All of 
this heat via one process or another will transfer to 
the oil, and pretty soon you should have hot oil. 
Now crack an egg, and you will find that it 
cooks—once again cover the pan with a sheet of 
glass. Of course, this trick requires the right sort of 
day—don’t expect fried egg on a cloudy day in 
Alaska! But if your climate permits, this is a nice 
trick! If there is not as much sun as you would 
like, try using reflectors to aim more solar energy 
onto your pan! 
In fact, with simple solar cooking, I have even 
heard of people baking cookies in their car by 
simply putting a black baking tray with cookie 
dough on their dashboard, and parking the car in a 
sunny setting with the windows up. They then 
return to the car at lunch to find a tray of cookies 
and a “bakery fresh” smelling car. It sure beats a 
Magic Tree for in-car air freshening! 
Online resources 
The following link is a great solar cooker site 
written specifically for younger kids. 
pbskids.org/zoom/activities/sci/solarcookers.html
49 
Project 10: Cook Eggs on Your Driveway 
Project 10: Cook Eggs on Your Driveway Using the Sun 
Figure 6-5 Solar egg frying.
You will need 
. Sheet of thin MDF 
. Sheet of flexible mirror plastic 
. Sheet of thin polystyrene 
. Veneer panel pins 
Tools 
. Bandsaw 
. Pin hammer 
. Sharp knife/scalpel 
. Angle marking gauge 
This solar cooker is a very simple project to 
construct—we will be harnessing the sun’s energy 
from a relatively wide area and concentrating it to a 
smaller area using mirrors (read more in Chapter 8 
about this). The area which we will concentrate it 
into will be lined with polystyrene to keep in 
the heat. 
Construct a box for your cooker out of MDF. I 
find small veneer pins to be very useful as they can 
be hammered neatly into the end grain of thin MDF 
without splitting the wood. For this application 
they are perfectly strong enough. When you have 
finished the box it should look something like 
Figure 6-6. 
Now you need to line the box with polystyrene, 
this will prevent the heat from escaping. The lined 
box will look like Figure 6-7. 
Now measure the size of the cube inside the 
lined polystyrene box. You should cut the mirror 
plastic to this size, and further line the box with it. 
Duck Tape is more than ideal for making good all 
of the joints and securing things into place. 
We now need to cut the mirrored reflectors. Cut 
a strip of mirror plastic about two feet wide on the 
bandsaw. Now, using an angle marking gauge, 
mark from the long side of the mirror to the very 
corner of the mirror, a line which makes an angle 
of 67°, forming a right-angled triangle in the scrap 
piece of plastic. You now need to mark out a series 
of trapeziums along this length of mirror, where 
50 Project 11: Build a Solar Cooker 
Project 11: Build a Solar Cooker 
Figure 6-6 The box constructed from MDF. Figure 6-7 The box lined with polystyrene.
the shortest side is equal to the length of the inside 
of the box cooker (Figure 6-8). 
Now take the mirrored reflectors, and on the 
nonreflective side, use Duck Tape to join them 
together to form the reflector which will sit on the 
top. Using Duck Tape allows you to make flexible 
hinges, which allow the reflector to be folded and 
stored out of the way. 
When the cooker is finished it will look like 
Figure 6-9. It is now ready for cooking! 
51 
Project 12: Build a Solar Camping Stove Figure 6-8 The mirrored reflectors cut ready. 
Figure 6-9 The solar cooker ready and complete. 
Project 12: Build a Solar Camping Stove 
You will need 
. Five sheets of A4 or U.S. letter size cardboard 
. Tin foil 
. Glue 
. Adhesive tape 
Tools 
. Scissors 
This is an incredibly simple construction for a 
solar camping stove. 
Simply, take five sheets of cardboard—three of 
them should be joined together by their long edges, 
the other two should be joined up by their short 
edges. Make the joint using adhesive tape so that it 
is flexible. 
Now cover the two pieces you are left with in tin 
foil. Use glue to secure the foil. 
And that is it! Now all it comes to is setting up 
your stove. 
Determine which way the sun is facing, and 
orient the three panels so that they all face the sun, 
with the outer two tilted slightly inwards. Now 
take the two sheets, one will sit on the ground— 
the food stands on top of this. The second sheet 
should be slightly tilted up toward the can so that 
any overspill light which misses the food is 
reflected back onto it.
The beauty of this design is that it is very simple, 
can be assembled quickly, and fits into the space of 
a few sheets of cardboard in your backpack. 
The set-up cooker is illustrated in Figure 6-10. 
The Easy Lid Solar Cooker 
solarcooking.org/easylid.htm 
The Minimum Solar Box Cooker 
solarcooking.org/minimum.htm 
Heaven’s Flame Solar Cooker 
www.backwoodshome.com/articles/ 
radabaugh30.html 
The Cooking Family Solar Panel 
solarcooking.org/cookit.htm 
Inclined Box Type Solar Cooker 
solarcooking.org/inclined-box-cooker.htm 
Sun Pan Solar Cooker 
www.sungravity.com/sunpan_overview.html 
Nelpa Solar Cooker 
solarcooking.org/nelpa.htm 
Pentagon Star Coooker 
solarcooking.org/PentagonStar.htm 
Dual Setting Panel Cooker 
solarcooking.org/DSPC-Cooker.htm 
A cardboard and tinfoil cooker with two heat 
settings. 
Solar Funnel Cooking 
solarcooking.org/funnel.htm 
The Tire Cooker 
solarcooking.org/tire_eng.htm 
A solar cooker made from a recycled tire! 
Online resources 
There are a lot of folk out there who swear by solar 
cooking. All sorts of people have formulated 
different designs of solar cooker. While I have 
presented a few designs that have worked for me, 
there are many, many other different types of design 
for different applications. I highly recommend that 
you browse some of the following links in order to 
find the solar cooker that is right for you. 
The Tracking Solar Box Cooker 
solarcooking.org/Cookerbo.pdf 
Fresnel Reflector Cooker 
www.sunspot.org.uk/ed/ 
The Reflective Solar Box Cooker 
solarcooking.org/newpanel.htm 
Collapsible Solar Box Cooker 
solarcooking.org/collapsible-box.htm 
The Bernard Solar Panel Cooker 
solarcooking.org/spc.htm 
52 Project 12: Build a Solar Camping Stove 
Figure 6-10 The set-up solar stove. 
Continued
Solar cooking recipes 
Potatoes 
For a start, cooking potatoes with a solar cooker differs 
a bit from cooking them in a campfire, which 
you are probably used to, because if you wrap them 
in shiny reflective tin foil, the solar energy which 
you have gone to painstaking ends to concentrate 
onto the potato will simply be reflected! 
Brewing tea 
If you want to brew tea in a solar cooker, you can’t 
expect to get boiling water and then make your tea 
conventionally—instead take a jar and a couple of 
tea bags, put the tea bags in the jar along with 
some clean water (which you might have even got 
from your solar distilling apparatus!). 
Soups 
Soups are really easy to cook in a solar cooker. 
Furthermore, they are particularly forgiving if the 
amount of sunlight is suboptimal, as warmish 
vegetable soup is quite acceptable whereas rawish 
not fully cooked chicken is totally unacceptable! 
Nachos 
Everyone loves Nachos! So why not take a bag, 
spread them in a bowl and cover with grated 
cheese. Then place the bowl in your solar cooker 
to melt the cheese and give you toasty hot nachos! 
Bread 
Take some old baked bean tins and paint them 
black—you now have the perfect can for cooking 
bread! 
To cook some simple French bread you will 
need a packet of baker’s yeast, a tablespoon of 
sugar and a tablespoon of salt, five cups of white 
flour and a couple of cups of water. 
Baked potatoes 
This is a really nice cartoon about cooking 
potatoes in the sun. 
www.hunkinsexperiments.com/pages/potatoes.htm 
Online resources—cont’d 
Parvarti Solar Cooker 
www.angelfire.com/80s/shobhapardeshi/ 
twelvesided.html 
Windshield Shade Solar Cooker 
solarcooking.org/windshield-cooker.htm 
A solar cooker made from an old car 
windscreen reflector shade 
Double Angle Twelve Sided Cooker 
solarcooking.org/DATS.htm 
A simple cooker design from cardboard 
and tin foil 
Parabolic Solar Cooker 
www.sunspot.org.uk/Prototypes.htm 
A solar cooker with an aluminum reflector 
and card base 
Solar Bottle Pasteurizer 
solarcooking.org/soda-bottle-pasteurizer.htm 
A pasteurizing device powered by the sun, 
and made from recycled materials 
Solar Water Pasteurizer 
solarcooking.org/spasteur.htm 
Solar Chimney Dehydrator 
www.littlecolorado.org/solar.htm 
Simple plans to build a food drying device 
powered by the sun 
Solar Cooking in the Peruvian Andes 
www.sunspot.org.uk/Solar.htm 
Solar cooking in the developing world 
53 
Solar Cooking Recipes
Dissolve the yeast in one cup of slightly warm 
water. Sift all of the dry matter into a clean bowl, 
stir in the yeast—water mix, add the water from 
the second cup in small amounts until the dough is 
sticky. Grease a baked bean can which has been 
painted black, being careful of any sharp edges, 
add the bread mixture and leave it in your solar 
oven. 
Solar cooking tips 
In many campsites and caravan parks, open fires 
are banned because of the mess they produce and 
the smoke which can be unpleasant for other 
visitors—so while everyone else has run out of gas 
in their cylinder, or is eating cold raw food, now 
would be a great time to crack open the solar 
cooker and make the rest of the campsite jealous! 
You really want to cook on days when the sky is 
clear and the sun can easily be seen—on a cloudy 
day, cooking will be painfully slow. 
One of the great things about solar cooking is 
that you can prepare everything in advance, leave 
it in your solar cooker, and when you return everything 
is cooked ready to eat—whereas your 
accomplices cooking with traditional methods still 
have to muck about and cook their food! 
Also—think like this—if you are cooking using 
conventional energy inside a home that is air 
conditioned, for every kWh of energy you input to 
your cooker, your air conditioning will use about 
another three trying to remove that heat from your 
home! 
54 Solar Cooking Tips
Solar Stills 
Chapter 7 
Water—a precious 
resource 
The former World Bank Vice President Ismail 
Serageldin, said that “the next world war will be 
over water.” 
At first look, this statement seems almost nonsensical, 
we are surrounded by water, it falls from 
the skies and runs through our streams and rivers; 
however, not all of the world enjoys such plentiful 
access to water as we do in the developed 
world. 
In much of the developing world the land is arid, 
and clean drinking water can often mean a walk 
for tens of miles. This problem is exacerbated by 
heavy industry building factories which extract 
what little water there is. 
Our water is constantly recycled by the natural 
environment, it follows a pattern called the hydrological 
cycle, which can be very simply represented 
by Figure 7-1. 
Water evaporates from the earth, plants, animals, 
and people, is carried far up into the sky where it 
condenses to form clouds—then it precipitates 
back to earth in the form of rain. 
This has a purifying effect on the rainwater, 
as when the water evaporates, contaminants are 
left behind—or at least this used to be the case— 
sulfur dioxide and other nastiness in the air 
from human activity can be collected by the 
rain as it precipitates, with the effect that when 
it lands on the earth, it is acidic. This can cause 
problems for plants and alkaline rocks, which 
are damaged by the acid content of the rain. 
A solar still effectively creates the hydrological 
cycle in miniature in an enclosed volume. The idea 
is that by evaporating water, all of the bacteria, 
salts and other contaminants are left behind, with 
the precipitate being pure, drinkable water. 
Even seawater can be desalinated using this 
process. 
There are a number of advantages to solar 
distillation: 
. Free energy 
. No prime movers required 
History of the solar still 
Solar stills are an old, tried and tested technology— 
the earliest record of a solar still being used is in 
1551, when Arab alchemists used one to purify 
water. 
Mouchot, whose name also springs up a couple 
of other times in this book also worked with solar 
distillation around 1869. 
55 
Figure 7-1 The hydrological cycle. 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
The first solar still, in the sense that we would 
recognize it now, was built in the mining community 
of Las Salinas in 1872, in the area which is 
now northern Chile. It was created by a Swedish 
technologist by the name of Charles Wilson. The 
plant was massive, about 4,700 square meters— 
quite an engineering feat for the time. 
The plant produced in excess of 6,000 gallons of 
water a day. 
The plant was effective and produced water well 
into the 20th century until it was finally closed in 
1912. All that remains now are shards of glass and 
salt deposits in the area where the stills were originally 
constructed. 
56 Project 13: Build a Window-Sill Demonstration Solar Still 
Project 13: Build a Window-Sill Demonstration Solar Still 
You will need: 
. Pint glass 
. Egg cup 
. Cling film/Saran wrap 
. Sellotape 
. Penny 
. Tea bag 
Tools 
. Scissors 
. Kettle 
This is a demonstration of how solar still technology 
works. It works great as a science fair demonstration 
piece, and is of a size that you can quickly 
put it together in a few minutes. This is how it 
works. 
First of all, we are going to make our water brackish. 
The best way to do this is to put the kettle on! 
A few minutes later, after making a brew you have 
black tea. Allow the teabag to sit in the water for 
some time until the water is quite “muddy.” 
Now put your egg cup in the bottom of the pint 
glass, and while holding the egg cup out of the 
way, carefully pour the tea into the bottom of the 
“still” making sure not to get any in the egg cup. 
Now take some clear plastic such as cling film/saran 
wrap and stretch it over the top of the pint glass. 
You might want to anchor it around the perimeter of 
the glass using a little bit of Sellotape just to make sure. 
You will want to stick your finger into the plastic in 
order to stretch it a little bit and create a dip above the 
egg cup. Be careful not to stick your finger through! 
You might want to put a little weight, such as a 
small coin, here in order to preserve the dip. Your 
whole assembly should now look something like 
Figure 7-2. 
Figure 7-2 Demonstration solar still.
Put the glass on a south-facing window sill and 
leave it for a couple of days. After some time, the 
plastic on top of the still will look something like 
Figure 7-3. 
This water should taste clear and pure, not 
“brackish” (i.e. strong tea!). 
Now you have proved the operation of the solar 
still! 
57 
Project 14: Build a Pit-Type Solar Still Figure 7-3 Precipitated water in the demonstration still. 
Project 14: Build a Pit-Type Solar Still 
You will need: 
. Polythene sheet 
. Cup 
. Tube 
. Rocks 
Tools 
. Spade 
This type of solar still is ideal if you are camping 
in a hot climate or stuck in the desert and you need 
to extract some clean drinking water. 
First of all, you will need to dig a hole with a 
spade. In this hole, you can place green plants, 
cacti, pots of brackish water or anything else 
you can gather that could potentially be water 
bearing. 
In the middle of this hole, you need to put 
a small cup, bowl or receptacle for water. A 
tube runs from this receptacle to outside the 
hole. Water can be extracted using this tube 
without having to upset the solar still or dismantle 
it. 
Over the top of the still you need to put a clear 
polythene sheet. This should be weighted down 
around the edges using rocks and stones. A small, 
light weight should be put in the center dip in 
order to let the water settle to a point for collection. 
This is shown in Figure 7-4. 
Water will precipitate and collect in the receiving 
vessel over time. In order to collect the water, 
just give a little suck on the pipe as shown in 
Figure 7-5 and pure water will come from the 
still. 
Warning 
On any camping expedition, remember to take 
sufficient water with you for the amount of 
people and time you will be away. This type of 
still should only be used as a demonstration or in 
emergencies, and does not provide a consistent 
reliable method for providing water for your 
travels, beyond basic, emergency needs.
You will need: 
. Plywood/oriented strand board 
. Framing 
. Screws 
. Glazing (glass/polycarbonate) 
. Metal U-strip 
. Black silicone 
. Low-profile guttering 
. Low-profile guttering end pieces 
. Tube 
. Two stop cock valves 
58 Project 15: Build a Solar Basin Still 
Figure 7-4 Diagram of a pit solar still. 
Figure 7-5 A solar still in operation. Image courtesy © U.S. Department of Agriculture—Agricultural Research Service. 
Project 15: Build a Solar Basin Still
Tools 
. Jigsaw 
. Screwdriver 
. Squeegee 
This project is scaleable depending on your requirements 
for water, which is why no specific measurements 
are presented. 
First of all, you will need to calculate your water 
needs. Solar stills can generally produce around a 
gallon of water per 8 square feet, this is around 
four liters per square meter. This assumes that your 
collector receives 5 hours of good sunlight per day. 
Obviously the performance of your still will be 
highly variable, depending on the amount of sun 
your collector receives. 
You need to construct a wooden box from plywood 
or oriented strand board, with gently sloping 
sides. This is well within the capability of someone 
with even modest carpentry skills. 
At a position near the tallest side of the box you 
will need to drill a hole and insert a pipe with a 
valve that can be opened and shut, to allow you to 
introduce brackish water to be purified. 
Then, take a squeegee and some black silicone. 
You need to spread this mixture on the bottom face 
of the wooden box so that it gets a thin uniform 
coat. Less important are the sides, but you should 
ensure that by the time you are finished, the inside 
of the box is fully lined with silicone. 
At the front of the still, that is to say on the 
shortest side of the box, you need to make a small 
gutter. This gutter will serve to collect your purified 
water which will run down by the force of 
gravity from your glazing. You need to make this 
gutter out of a waterproof material. The low-profile 
guttering sold for sheds and outbuildings is ideal. 
A hole needs to be drilled in the side of the frame 
of your still, and a pipe introduced to allow you to 
siphon off the clean water. 
The silicone has two functions. First of all, 
it acts as a black collector surface, absorbing 
radiation and creating heat. But secondly, it protects 
your wood by making the enclosure waterproof. 
On top of this sealed box you need to put a sheet 
of glazing. This needs to be sealed around the 
edges with frame sealant to ensure a good watertight 
fit. 
The brackish water should never be allowed to 
rise above the level of the guttering, as it would 
contaminate the clean water. The whole solar still 
is illustrated diagrammatically in Figure 7-6. 
59 
Project 15: Build a Solar Basin Still 
Figure 7-6 Diagram of the basin type still.
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Solar Collectors 
Chapter 8 
The sun provides an abundance of energy over a wide 
area; however, often our solar devices are fairly 
small, and so receive little solar energy. So—what if 
we could take the solar energy from over a wide area, 
and concentrate it into a smaller area? This makes a 
lot of sense, because it means that the small area 
receives a much higher amount of solar radiation. 
So what can solar 
collectors actually do? 
Actually, the sun has quite a phenomenal power— 
when concentrated into a small area, its power is 
truly extraordinary. If you were a ghastly child you 
might have burnt ants using a magnifying glass— 
well what goes around comes around: remember 
that when a large ethereal figure holds a magnifying 
glass over you. One of my memories of junior 
school was gathering in a corner of the playground 
where a group of children were concentrating the 
sun onto some logs covered in tar and making 
smoke. Although we did not know it then, we had 
made a solar collector. 
The chances are you’re getting tired of reading 
this, but “this is not a new concept,” in fact, the 
Greek’s purportedly had a “weapon of mass 
destruction,” that harnessed the power of the sun to 
set fire to enemy boats. 
Archimedes—you may have heard of him—he 
found a few things out, like the concept of the 
Archimedes screw and the theory of displacement. 
Anyway, it is fabled that he had a weapon that was 
created out of mirror-like bronze that he could use 
as a death ray—this ray essentially reflected 
concentrated sunlight! 
In the book Epitome ton Istorion, John Zonaras 
wrote: “At last in an incredible manner he burned 
up the whole Roman fleet. For by tilting a kind of 
mirror toward the sun he concentrated the sun’s 
beam upon it; and owing to the thickness and 
smoothness of the mirror he ignited the air from 
this beam and kindled a great flame, the whole of 
which he directed upon the ships that lay at anchor 
in the path of the fire, until he consumed them all.” 
This deadly weapon was allegedly used in the siege 
of Syracuse in 212 BC—like I said, the idea is old! 
So this is what MIT did . . . 
First they got loads of students on the 2.009 
course, loads of chairs to act as stands and loads of 
mirrors (Figure 8-1). Being MIT, they got the cash 
for this kinda stuff! 
Next they lined all the mirrors up so that the sun’s 
energy was concentrated onto the model of the 
hull of a boat—voila!—or should that be Eureka? 
Flames! (Figure 8-2) 
Here we can see the serious damage done by the 
flames to the wood (Figure 8-3)! With a larger mirror 
area this could have been a formidable weapon! 
In Figure 8-4 we see how MIT used a similar 
technique to the one you will use in the next 
project—cover each mirror up with paper, line 
each one up individually by removing the piece 
of paper and adjusting the mirror. And then, 
when they are all lined up, remove all the bits of 
paper as fast as you can without disturbing the 
mirrors! 
And as ever, with every serious piece of technological 
investigation, there is the back of the paper 
bag calculation (Figure 8-5). 
Now it’s your go! 
61 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
62 Solar Collectors 
Figure 8-1 Students, chairs and mirrors! Image courtesy Massachusetts Institute of Technology. 
Figure 8-2 The boat catches fire—Archimedes was right. Image courtesy Massachusetts Institute of Technology.
63 
Solar Collectors 
Figure 8-3 The burnt hull. Image courtesy Massachusetts Institute of Technology. 
Figure 8-4 Lining up the mirrors. Image courtesy Massachusetts Institute of Technology.
You will need: 
. Sheet of MDF 
. Sheet of flexible mirror acrylic 
. 72 long self-tapping screws 
Optional 
. Silicone sealant 
Tools 
. Drill bit 
. Hand/cordless drill 
. Glue gun and sticks 
. Ruler 
. Set square 
. Bandsaw 
Optional 
. Mastic gun 
OK, so you have finally decided—the time is nigh 
to melt your little brother. While he might be hard 
to melt, you can certainly singe him with this modular 
solar death ray! 
Don’t worry—you won’t need lots of chairs and 
big A4 mirrors like the guys at MIT! Instead, this 
modular death ray relies on little tiles which are 
cut from plastic mirror. 
The plan is really simple—you build the death 
ray a tile at a time. One tile is good to experiment 
Warning 
I have used acrylic mirror in this project because 
it is very easy to work with, and can be cut easily 
using a band saw; however, there is nothing to 
stop you using a glass mirror if it is available and 
you have the correct tools to cut it and work with 
it—my only advice is it will be harder to work 
with and much more fragile. 
64 Project 16: Build Your Own “Solar Death Ray” 
Figure 8-5 Working it all out! Image courtesy Massachusetts Institute of Technology. 
Project 16: Build Your Own “Solar Death Ray”
with, but once you become more confident and 
want to expand, you can simply add more tiles! 
To begin with, I recommend that you cut yourself 
a piece of MDF that is 36 cm square, although 
please bear in mind that this measurement is wholly 
arbitrary. 
Now using a ruler and set square, divide the 
sheet into a matrix of six squares by six squares. 
This will give you thirty-six equal squares 6 cm 
square. Now, using the ruler and set square, draw a 
line 1 cm either side of each line making up the 
squares. This will leave you with a sheet that does 
not look dissimilar to Figure 8-6. 
You are now going to drill holes for the screws 
that will support the mirrors. You will need to 
select a drill that is slightly smaller than the screw 
that you are going to drill the hole for. However, 
please note that the screw does not need to be a 
tight fit in the hole, as it would be if you were 
joining two pieces of wood. Instead, the screw is 
only going to be used for light adjustment, so the 
screw can be a relatively slack fit in the hole. 
Looking at your board of squares, you are going 
to be drilling two holes in each 6 cm square. The 
holes will be at the top left and bottom right, 
where the lines cross to form the smaller square 
inside each square. Sounds confusing, well, take a 
look at the furnace drilling diagram (Figure 8-7), 
which shows where to drill in each square. 
Once you have drilled all 72 holes, you are 
going to need to think about getting those screws 
in place. This is a really tedious job, so either ask a 
younger sibling, or failing that, if you are an only 
child you might like to consider investing in an 
electric screwdriver—the lazy man’s way out. 
You want to put the screws in so that they just 
protrude from the other side a little way (Figure 8-8). 
Now is a good time to take your acrylic sheet 
of mirror, and, on a bandsaw, cut 36 identical 
65 
Project 16: Build Your Own “Solar Death Ray” 
Figure 8-6 Sheet of MDF marked out. 
Figure 8-7 Furnace drilling diagram. 
Figure 8-8 Solar furnace with the screws in place.
6 × 6 cm squares. An easy way to do this is to set 
the gate on your band saw to 6 cm from the blade. 
Take a couple of cuts from your mirror, to give you 
6 cm strips, and then cut these strips into squares 
using the gate at the same measurement. 
Once you have done this, you need to fix the mirrors 
to the base plate of the solar furnace. You need to pick 
a corner, which is different to the ones that the screws 
are positioned in, and stick to this corner. What you 
will be doing is applying a large glob of either glue or 
silicone sealant, into which the corner of the mirror 
tile is immersed. The other two corners are supported 
on screws, which permit adjustment of the tile’s angle 
relative to the base board (Figure 8-9). 
When all the mirrors are in place, stick a small 
removable piece of paper, for example a Post-It 
note to each of the mirrors. 
Set your collector up so that it faces the sun. Remove 
one of the pieces of paper in one of the corner mirrors—
notice where the light forms a bright patch and 
set up an object to be heated or piece of wood there. 
Draw an X where there is a bright patch. 
Now, one by one, using the screws for adjustment, 
you can change the angle of each individual 
mirror. Cover and uncover mirrors one by one 
using the Post-It notes—you will need to work 
quickly as you will find that the sun is constantly 
changing position. 
Eventually you will find that you can focus all 
of the mirrors onto a single point—this concentrated 
energy can be used for cooking, heating, or 
experiments (burning things!). 
Parabolic dish concentrators 
Dishes are great for concentrating dispersed energy 
to a focal point. Take a look at any residential neighborhood, 
and you are bound to see a menagerie of 
dishes (the state flower of Virginia) sticking out of 
the side of houses everywhere! What do you think 
these dishes are doing? Acting as concentrators! 
They take the waves emitted from satellites far above 
the earth’s surface, and concentrate them into a focal 
point which strengthens the signal. Similarly, you 
might have seen some of the world’s great radio telescopes 
perched up high upon hillsides. These are 
doing exactly the same thing, taking the signal from 
a wide area, and focusing it down to a small point. 
They are “concentrating” the weak signals from outer 
space to a fine point where they can be processed. 
Solar concentrators using parabolic dishes are 
exactly the same, the difference being the medium 
used to coat the dishes. Rather than being reflective 
to radio waves, the coatings used to coat a parabolic 
solar reflector are mirrors. 
Again this idea is not particularly new, in fact, 
back in the 1800s a Frenchman by the name of 
Augustin Mouchot was actively experimenting with 
using solar dishes to concentrate the sun’s energy. 
Mouchot was concerned that coal was all going to 
be used up and that “Peak Coal” was approaching. 
He said at that time “Eventually industry will no 
longer find in Europe the resources to satisfy its 
prodigious expansion . . . Coal will undoubtedly 
be used up.” One of Mouchot’s solar concentrators 
can be seen in Figure 8-10. A little later in 1882, 
Abel Pifre, Mouchot’s assistant, demonstrated a 
printing press in the Tuilleries Garden, Paris, powered 
by the sun, using a 3.5 m diameter concave concentrating 
dish. At the focus of this concentrating furnace, 
66 Project 16: Build Your Own “Solar Death Ray” 
Figure 8-9 Board with mirrors stuck on starting to 
take shape!
was a steam boiler which provided steam for the 
printing press. A woodcut drawing of this press is 
shown in Figure 8-11. 
Dishes are great for concentrating dispersed energy 
to a focal point (Figure 8-12a and b). Take a look at 
Figure 8-13 which shows parallel rays of light, entering 
a parabola and being focused to a point. 
Note 
If you want a cheap source for a solar parabolic 
mirror, the University of Oxford produce a solar 
energy kit (Figure 8-14), which is inexpensive, and 
comes with a budget plastic parabolic mirror. 
67 
Parabolic Dish Concentrators 
Figure 8-10 One of Mouchot’s solar furnace dishes. 
Figure 8-11 Pifre’s solar printing press.
68 Parabolic Dish Concentrators 
Figure 8-12a and b Parabolic mirrors take incoming parallel light (from the sun) and focus it to a point. 
Figure 8-13 Diagram showing how parabolas focus light to a point.
You will need 
. Old satellite dish 
. Bathroom/kitchen tile adhesive 
. Small mirror tiles 
Tools 
. Adhesive comb 
. Spreader 
This is an incredibly easy way to make a parabolic 
dish concentrator, and even better, it recycles old 
stuff! Take a satellite dish, and dunk your adhesive 
comb into the bathroom/kitchen tile adhesive. 
Working from the center of the dish outwards, spread 
the adhesive using the “comb” side of the spreader. 
What the comb does is apply the adhesive in a 
ridged manner, this means that when you press the 
tiles into the adhesive, they have room to settle and 
even themselves out. If you just apply straight flat 
adhesive, when you try to push the tiles in, 
adhesive will ooze out everywhere and make a 
mess. As you work from the center, keep adding 
more tiles, trying as best you can to keep them in 
line with the plane of the parabolic satellite dish. 
Caution 
I strongly recommend that you perform this operation 
in your garage or in a shaded area, as with the addition 
of more mirrors and a little sunlight, a focal 
point can quickly develop which has the potential to 
burn you while you are working! 
Note 
You need to purchase some tile adhesive—the sort 
of stuff you would use when applying ceramic tiles 
onto your walls at home. 
You will need to choose a tile adhesive which 
is waterproof, as a non-waterproof tile adhesive 
will not stand outside use—for this purpose 
kitchen/bathroom adhesive is strongly recommended. 
69 
Project 17: Build Your Own Parabolic Concentrator 
Figure 8-14 University of Oxford solar energy kit. 
Project 17: Build Your Own Parabolic Dish Concentrator
Free energy? 
Solar dish collectors take the immense power of 
the sun, over the area of a dish, and concentrate 
that energy by means of reflectors to a central 
point. 
At the end of 2004, Sandia National Laboratory 
announced that they were working with Stirling 
Energy Systems to build and test a six-dish array. 
These six dishes would be capable of producing 
150 kW of power during the day, enough to power 
40 homes. 
Each dish comprises 82 individual mirrors all 
focused to a single central point (Figure 8-15). This 
causes a massive amount of heat to be generated at 
that point which is used to drive a Stirling engine. 
The Stirling engine produces mechanical movement, 
which is converted to electrical energy by a conventional 
generator arrangement (Figure 8-16). 
One of the problems inherent with solar dish 
systems is that they must track the sun—older 
systems used really heavy mirrors which meant 
that the motors required to track the sun had to be 
big and beefy and drew a lot of energy. With this 
new array of collectors, the mirrors have been 
designed with a honeycomb structure so they are 
strong, and yet very light indeed. 
This is said to be the largest array of solar dishes 
in the world, but big plans are afoot. Eventually, 
when the technology is fully proven, massive 
arrays of 20,000 units are imagined filling vast 
fields and plains—producing free energy from the 
sun (Figure 8-17). 
Note 
If you are messy and get adhesive everywhere, you 
want to wait a little while until the tiles are firmly 
in place, but not so long as for the adhesive to dry, 
as it will only be harder to get off once it has set. 
To remove adhesive while it is still wet, you need a 
moist cloth, which you can wipe over the surface 
of your mirror tiles, taking off any excess adhesive 
with the cloth. 
70 Project 17: Build Your Own Parabolic Concentrator 
Figure 8-15 Solar dish engine system under test. Image courtesy Sandia National Laboratories/Randy Montoya
71 
Free Energy? 
Figure 8-16 10 kW solar dish Stirling engine water pump. Image courtesy Sandia National Laboratories/ 
Randy Montoya. 
Figure 8-17 Artist’s rendering of a field of solar engines. Image courtesy Sandia National Laboratories/ 
Randy Montoya.
You will need 
. Fresnel lens 
. Feather 
. Small piece of rubber 
. Wax candle 
. Photovoltaic cell 
. Multimeter 
Imagine trying to build a large lens to cover a meter 
square in order to concentrate the sun. What would 
you build it out of? Well for a start, the lens would 
be physically quite big if it had to cover a meter 
square, it would also use quite a large volume of 
material. This is not a particularly efficient way of 
doing things. Far better to build a lens that uses less 
material. This has a number of advantages. First of 
all, it uses less material. As a result of this, the lens 
is not only cheaper, but also lighter. This means if 
our lens is actively tracking the position of the sun 
by a mechanism, the mechanism can be lighter duty, 
as it does not need to move such a heavy load. 
Where can I get a 
Fresnel lens? 
Here are a few ideas for procuring a Fresnel lens, 
both second hand and new, cost varies widely: 
Car reversing lenses are a great source, like 
those pictured in Figure 8-18, these are often fairly 
small with a fairly coarse lens, but will certainly 
do the job and provide many fun hours of 
experimentation! 
Fresnel lenses are often sold in small credit card or 
slightly larger sized flat plastic printed versions in 
bookshops. They are often sold as a bookmark, 
which doubles up as a text magnifier for those with 
poor sight. These lenses are not normally that large; 
however, they have quite a finely ruled lens structure. 
Overhead projectors are another great source of 
Fresnel lenses. If you can find an old projector which 
is being discarded, the Fresnel lens is the surface on 
which you would place the transparency. As many 
people are now switching to video projectors and 
presentation software, colleges and schools are often 
great places to find unwanted overhead projectors. 
Old large screen projection televisions are another 
item that sometimes use large Fresnel lenses to 
Note 
Very large Fresnel lenses can generate truly 
awesome power—start the experiments in this 
chapter with smaller Fresnel lenses such as those 
used as “magnifying bookmarks” before 
graduating to larger lenses! 
72 Project 18: Experiment with Fresnel Concentrators 
Project 18: Experiment with Fresnel Lens Concentrators 
Figure 8-18 Car reversing Fresnel lens.
make the picture larger. This will involve a bit of 
disassembling—so make sure you are with someone 
who knows what they are doing. Try to find an old 
broken set, not your father’s latest HDTV wonder if 
you want to live to see your next birthday! 
Also, for a nice-sized meaty Fresnel lens, you 
can often find plastic screens that you put in front 
of your TV in order to make it appear bigger. 
If all else fails, a quick Google search will throw 
up a few results for optical suppliers. There are a 
lot of vendors selling kits to make large-screen 
projector TVs from an old screen—these lenses are 
often very overpriced. Online auction sites are 
another good source, or school science catalogs. 
There are also a couple of entries in the Supplier’s 
Index (see Appendix) for new Fresnel lenses. 
How does a Fresnel lens work? 
To understand how a Fresnel lens is constructed 
and works, we are going to need to do a little 
thought experiment. Picture this. You have a glass 
lens which is flat on one side, and round on the 
other. We are now going to use a tool to remove 
material from the center point of the lens. The tool 
has a flat end. We are going to remove material 
until the corners of the flat-ended tool just begin to 
penetrate the round surface. We are now going to 
use another larger tool to remove material from a 
circle around the last. We are going to do this until 
the tool just starts to break through the surface. We 
are going to keep doing this with progressively 
larger tools until we are left with a hollowed lens. 
If you were to look at the inside of this lens, 
what you would see is a series of flat “steps” cut in 
concentric circles. Now imagine flattening out 
these concentric circles so that they all lay in the 
same plane. What you have constructed in your 
mind is a Fresnel lens. 
Take a look at Figure 8-19, it shows how a 
Fresnel lens is simply a normal lens with the 
unnecessary glass removed and flattened. It is 
important to note, that although Fresnel lenses tend 
to be lighter, they do not possess the same optical 
clarity as ordinary lenses—which is why they are 
not used in cameras or microscopes. 
Take a look at Figure 8-20. It demonstrates that 
although our Fresnel lens is only a thin sheet of 
plastic, it can magnify things significantly. 
Now try and use your Fresnel lens as a solar 
concentrator, hold it above a piece of paper until 
you form a bright white dot of sunlight (Figure 8-21). 
Notice how much brighter the concentrated dot is 
compared with the rest of the paper, which is 
simply illuminated by the sun. 
73 
Project 18: Experiment with Fresnel Concentrators 
Figure 8-19 Diagram showing how a Fresnel lens 
compares to a conventional lens. 
Figure 8-20 A thin Fresnel lens shown magnifying.
A few experiments that you 
can do with a Fresnel solar 
concentrator 
Use a thermometer to measure the temperature of 
the point where the sun’s energy is concentrated— 
see what difference it makes if the bulb is covered 
in tin foil or black paper. 
The intensity of the concentrated light might be 
enough to singe a feather, or even a thin shaving of 
rubber from a balloon or latex glove. 
Try shining the beam of light onto a photovoltaic 
cell connected to a multimeter and load—see how 
it affects the amount of power produced. 
You might also want to see if you can melt a wax 
candle using the power of your concentrated light. 
74 Project 18: Experiment with Fresnel Concentrators 
Figure 8-21 Concentrating solar energy using a Fresnel lens.
Pumping water is an essential task—we need water 
to drink, wash, cook, and sanitize and irrigate with. 
Water can be used for utility, or it can be used for 
dramatic effect, creating tranquility and pleasantness 
in our surroundings. 
Using solar energy to pump water makes quite 
a bit of sense. Our demand for water often rises 
when the sun is shining. Think of agriculture— 
there is more sun in the summer, and that is 
when we want pumped water to irrigate our 
crops. 
We can use water features to enhance our environment, 
water naturally has a calming destressing 
effect, and its importance is emphasized by disciplines 
such as Feng Shui. 
Water can be used to add prestige to an area. 
The U.K. Centre for Engineering and Manufacturing 
Excellence (CEME) has a fountain outside, powered 
by solar photovoltaics on the roof. This can be 
seen in Figure 9-1. 
Similarly at home, you use your water features 
in the garden when the sun is shining, not when 
the sky is gloomy and the weather overcast. 
In this sort of application, the intermittency of 
solar energy does not matter so much. 
Also, water can be stored relatively easy. When 
we actually pump it to our location doesn’t really 
matter, as it can happily sit there in a tank. This 
means that we can use a supply tank to even out 
some of the intermittency problems. 
There are other solutions to the problem; even in 
low light, we can harness the energy that the sun 
produces and store it in capacitors. When the 
energy stored builds up to a sufficient level, a 
small amount of pumping can be performed and 
the cycle repeats again. This is shown in the 
display at the Centre for Alternative Technology, 
U.K. (Figure 9-2). 
This has some interesting consequences for our 
energy supply. The pumped power station at 
Dinorwig, Wales, draws water up into a large 
reservoir using excess power from the grid. When 
there is a shortage of power, that water is allowed 
to flow down hill through hydroelectric generators, 
producing power as it does so. 
As we can see, there are many cogent reasons 
for using solar energy to pump our water—now 
let’s move on to some practical projects: 
75 
Chapter 9 
Solar Pumping 
Figure 9-1 Photovoltaic-powered fountains enhance 
the CEME, U.K. 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
Adding a solar-powered fountain to your school, 
home, or office is a great way to create a peaceful 
relaxing atmosphere. The modern world demands a 
lot of us, and it is nice to have some space where 
we can quietly go and relax and listen to the 
soothing sound of trickling water. 
First of all, you need to decide what sort of 
fountain you want. There are a number of different 
options here—you might want a plume of water 
jetting into the air, you might like to add a trickling 
brook waterfall to your garden, or you might want 
a bell shaped fountain. 
Once you have decided on your feature, nip down 
to the garden center to see what fixtures and fittings 
they have in store. Regular pump fittings will often 
specify the flow rate of the fixture, this essentially 
means what volume of water can be pumped at what 
rate, and also how high the water can be pumped. 
We call this the “head” of water. We will size our 
pump appropriately to produce this head of water. 
As a rough guide, a calm, trickling waterfall will 
demand between 1 and 2 gallons per minute (gpm), 
or between 3 and 8 liters per minute (lpm) if you 
are working in metric. 
For something with a little more razzmatazz, 
you might like a plume of water shooting into the 
air. This will generally demand a little more water, 
say 4–7 gpm or 15–27 lpm. 
If you want the whole shebang with a cascading 
waterfall with a heavier current, then you really 
need to be considering flow rates of around 7–16 
gpm, which works out as around 27–60 lpm. 
Tip 
If you need to convert flow of water between metric 
and imperial, I suggest you nip along to: 
www.deltainstrumentation.com/calcs.html 
76 Project 19: Build a Solar-Powered Fountain 
Figure 9-2 The solar pumping display at the Centre for Alternative Technology, U.K. 
Project 19: Build a Solar-Powered Fountain
Manufacturer’s figures can often be optimistic 
and sometimes unreliable. While the minutiae 
sometimes don’t matter, if you want to be sure and 
test flow rate, all you need is a gallon bucket and a 
stopwatch. Time how long it takes to fill up the 
bucket. 
When you go to choose your pump, you need to 
realize that there are pumps, and there are pumps! 
The type that you require is a “DC submersible 
pump.” A submersible pump is already waterproofed 
and will happily sit in the sump of your 
water feature. It sucks the water from the sump, 
and forces it out through a pipe. One of the 
beauties of this type of pump is that it does not 
require “priming,” a procedure which is tiresome 
and often required by some other pumps. 
You need to pick a pump that has a similar 
power rating to your solar array. Keep everything 
to 12 V, and if at all possible, oversize the solar 
panel slightly to give you adequate performance in 
poorer weather. 
If you can’t find a source of low-voltage DC 
pumps, then take a trip to your local chandler or 
boat shop. They will often sell low-voltage pumps 
that are used to pump water out from the bottom of 
boats. These are known as “bilge pumps” and 
shouldn’t cost a lot of money. 
In order to keep things nice and simple, we are 
just going to connect our solar panel directly to our 
pump (see Figure 9-5). This is nice because it allows 
you to visually observe the relationship between the 
water flowing through your feature, and the amount 
of sunlight falling on your panel. It does, however, 
mean that in overcast weather your feature will 
Siting your panel 
You might want to heed the guidance given in some 
of the other chapters in this book on correctly siting 
your solar panel. Furthermore, you want to ensure 
that your solar panel is correctly insulated and 
protected against the elements. The waterproof solar 
panel showcase in Figure 9-3 is ideal and furthermore, 
looks attractive. 
Don’t hide your panel, proudly display your solar 
credentials, make it a part of the feature, as shown in 
the solar fountain at CAT (Figure 9-4). 
Hint 
Remember the 10:1 rule for working out horizontal 
distances of pipe. First of all, it assumes you are 
using pipe that is about 1/2 in. or 12 mm. It requires 
energy to pump water horizontally, so think to 
yourself for every 10 units horizontally, it is the 
same as 1 unit of head. 
Deciphering pump specifications 
When you buy your pump from the manufacturer, 
it will state on it a number of figures, it should tell 
you how high the pump will pump water, this is 
known as the head. Furthermore, it should also state 
the flow rate of the pump, which is how much water 
it will pump for any given period of time. What 
you need to realize, is that as you increase the 
demand for head, the flow rate will suffer. This is 
really important to bear in mind when selecting 
equipment. 
77 
Project 19: Build a Solar-Powered Fountain 
Figure 9-3 Waterproof solar panel showcase.
perform poorly, if at all; but then who wants to be 
outside when it is overcast! 
Next, before committing to a feature, take your 
pump, dump it in a bucket of water and connect it 
to your panel to check that everything is working. 
Check this setup in good light to ensure that it is 
your setup, not the sun which is the problem. 
Now you need to build a sump of some sort for 
your pump to sit in. Again, a trip to the garden 
center may yield a nice large-sized waterproof 
container, butt, or bucket. 
If you are feeling particularly energetic, you 
could dig a hole in the ground, line it with fine 
sand, ensuring that there are no sharp protruding 
edges, and then line it with a waterproof liner. 
You want your sump to be able to hold a fair 
quantity of water—the water in our feature will be 
recirculated, rather than constantly replenished. 
Ensure that when your submersible pump sits in 
the sump it is fully immersed in water. 
Figure 9-4 Solar panel on display. 
Figure 9-5 Diagram of the solar water feature. 
78 Project 19: Build a Solar-Powered Fountain
One you have satisfied yourself that your pump 
and module work together satisfactorily, you will 
need to install your feature. 
Things to consider 
Flexible plastic tubing and jubilee clips are infinitely 
easier to work with than copper pipe and solder. 
You will want to provide some sort of mechanical 
protection for your cable to ensure that it does not 
become chafed, or cannot easily be damaged by 
gardening activities such as digging. Encase the 
pipe in a hard plastic pipe, or mount it above 
ground where it can clearly be seen. 
Hint 
Because of the low-voltage, low-current nature of 
a single photovoltaic module connected to a 
pump, many region’s electrical codes will not 
require a fuse, breaker, or other disconnection 
device; however, check your local regulations to 
be on the safe side. 
79 
Project 19: Build a Solar-Powered Fountain
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Solar Photovoltaics 
Chapter 10 
A solar photovoltaic device is one which takes 
light from the sun and turns it into electricity. In 
doing so, it produces no emissions or harmful 
waste, and does so completely silently! 
The origin of photovoltaic 
solar cells 
None of this would be possible if it hadn’t been for 
the work of French Physicist Edmund Becquerel, 
who in 1839, discovered the photovoltaic effect. In 
fact, Becquerel is a bit of an inspiration for young 
HomeBrewPoweres wanting to experiment with solar 
energy, as he made his discoveries when he was 
only 19! In 1883, Charles Fritts, an American 
inventor, devised the first practical solar cell, when 
he took some selenium and covered it with a fine 
coating of gold. His cell wasn’t particularly efficient, 
with 1% or so conversion efficiency from light to 
electricity; however, his design of cell later found 
applications as a sensor in early cameras to detect 
the light level—being used to “sense” light rather 
than to generate power in any real quantity. Albert 
Einstein went on to further develop the theory of 
the nature of light and the mechanism through 
which the photoelectric effect works, the discovery 
was considered so important that he won the Nobel 
Prize in 1905. Because of their high cost and low 
efficiency at that time, there were a lack of 
applications for photovoltaic cells. It was not until 
Bell Laboratories started looking at the idea again 
in the 1930s that Russell Ohl discovered the silicon 
photovoltaic cell. This device was patented as 
Patent no: US2402662 “Light sensitive device.” 
Now the efficiency of solar cells began to increase. 
The first generation of practical solar cells was 
horrendously expensive, and this severely limited 
their range of applications. The advantages of using 
photovoltaic cells to turn sunlight into electrical 
power were initially appreciated for powering 
satellites and space-missions. With the space race 
of the 1950s and 1960s, there was suddenly a 
good application for solar cells—despite the cost, 
solar cells were suitable for generating energy in 
the remote reaches of space. Vanguard 1 was 
launched on March 17, 1958, and was the first 
artificial satellite to employ solar photovoltaic 
cells. With the injection of funding and research 
that came with the space race, solar cells began to 
come into their own. Over the years that followed, 
solar photovoltaic technologies have been refined 
and developed and new techniques explored. We 
are now at the point where we have a range of 
different photovoltaic technologies, and we will 
explore these now. 
Solar cell technologies 
There are a number of different technologies that 
can be used to produce devices which convert light 
into electricity, and we are going to explore these 
in turn. There is always a balance to be struck 
between how well something works, and how 
much it costs to produce, and the same can be said 
for solar energy. 
We take solar cells, and we combine them 
into larger units called “modules,” these modules 
can again be connected together to form arrays. 
Thus we can see that there is a hierarchy, where 
the solar cell is the smallest part (see Figure 10-1). 
81 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
In this chapter we are going to look at the structure 
and properties of solar “cells,” but bear in 
mind, when combined into modules and arrays, the 
solar “cells” here are mechanically supported by 
other materials—aluminum, glass, and plastic. 
One of the materials that solar cells can be made 
from is silicon—this is the material that you find 
inside integrated circuits and transistors. There are 
good reasons for using silicon, it is the next most 
abundant element on earth after oxygen. When you 
consider that sand is silicon dioxide (SiO2), you 
realize that there is a lot of it out there! 
Silicon can be used in several different ways to 
produce photovoltaic cells. The most efficient solar 
technology is that of “monocrystalline solar cells,” 
these are slices of silicon taken from a single, large 
silicon crystal. As it is a single crystal it has a very 
regular structure and no boundaries between crystal 
grains and so it performs very well. You can generally 
identify a monocrystalline solar cell, as it 
appears to be round or a square with rounded 
corners; you can see monocrystalline solar cells in 
Figure 10-2. 
One of the caveats with this type of method, as 
you will see later, is that when a silicon crystal is 
“grown,” it produces a round cross-section solar 
cell, which does not fit well with making solar 
panels, as round cells are hard to arrange efficiently. 
The next type of solar cell we will be looking at, 
also made from silicon, is slightly different, it is a 
“polycrystalline” solar cell. Polycrystalline cells 
are still made from solid silicon; however, the 
process used to produce the silicon from which the 
cells are cut is slightly different. This results in 
“square” solar cells. However, there are many 
“crystals” in a polycrystalline cell, so they perform 
slightly less efficiently, although they are cheaper 
to produce with less wastage. 
Now, the problem with silicon solar cells, as we 
will see in the next experiment, is that they are all 
effectively “batch produced,” which means they 
are produced in small quantities, and are fairly 
expensive to manufacture. Also, as all of these 
cells are formed from “slices” of silicon, they use 
quite a lot of material, which means they are quite 
expensive. 
Now, there is another type of solar cells, 
so-called “thin-film” solar cells. The difference 
82 Solar Photovoltaics 
Figure 10-1 Cells, modules and arrays. 
Figure 10-2 Monocrystalline solar cells made into 
a panel.
between these and crystalline cells is that rather 
than using crystalline silicon, these use chemical 
compounds to semiconduct. The chemical compounds 
are deposited on top of a “substrate,” that 
is to say a base for the solar cell. There are some 
formulations that do not require silicon at all, such 
as CIS (copper indium diselenide) and cadmium 
telluride. However, there is also a process called 
“amorphous silicon,” where silicon is deposited 
on a substrate, although not in a uniform crystal 
structure, but as a thin film. In addition, rather than 
being slow to produce, thin-film solar cells can be 
produced using a continuous process, which makes 
them much cheaper. 
However, the disadvantage is that while they 
are cheaper, thin-film solar cells are less efficient 
than their crystalline counterparts. Some different 
solar photovoltaic technologies are compared in 
Table 10-1. Figures are given for the efficiency of 
the cell technology, and the average area of cells 
required to generate 1 kW peak power when facing 
in the right direction! 
When looking at the merits of crystalline cells 
and thin-film cells, we can see that crystalline 
cells produce the most power for a given area. 
However, the problem with them is that they are 
expensive to produce and quite inflexible (as you 
are limited to constructing panels from standard 
cell sizes and cannot change or vary their shape). 
By contrast, thin-film cells are cheap to produce, 
and the only factor limiting their shape is the 
substrate they are mounted on. This means that 
you can create large cells, and cells of different 
shapes and sizes, all of which can be useful in 
certain applications. 
We are now going to take a detailed look at 
making two different types of solar cell, one will 
be a crystalline solar cell, and the other a thin-film 
solar cell. Both of the experiments are designed to 
be “illustrative,” rather than to actually make a cell 
with a useful efficiency. The technology required 
to make silicon solar cells is out of the reach of the 
home experimenter, so we are going to “illustrate” 
the process of how a solar cell is made, using 
things you can find in your kitchen. For thin-film 
solar cells, we are going to make an actual solar 
cell, which responds to light with changing 
electrical properties; however, the efficiency of our 
cell will be very poor, and it will not be able to 
generate a useful amount of electricity. 
How are crystalline 
photovoltaic cells made? 
In this section we are going to look at how photovoltaic 
cells (PV) are made. However, rather than 
taking a dull, textbook approach, we are going to 
make the whole process fun by doing some practical 
kitchen experiments that mimic the process that 
happens in solar cell factories all around the world. 
How do they work? 
First of all, let’s cover a little bit of the theory. 
Ordinary silicon forms into a regular crystalline 
structure. If you look at Figure 10-3, you can see 
the way that the silicon atoms align themselves 
into a regular array. 
To make silicon “semiconducting,” we can take a 
little bit of another chemical, in this case boron, and 
83 
Solar Photovoltaics 
Table 10-1 
Efficiency of different cell types 
Area required 
to generate 
1 kW peak 
Cell material Efficiency power 
Monocrystalline silicon 15–18% 7–9 m2 
Polycrystalline silicon 13–16% 8–11 m2 
Thin-film copper indium 7.5–9.5% 11–13 m2 
diselenide (CIS) 
Cadmium telluride 6–9% 14–18 m2 
Amorphous silicon 5–8% 16–20 m2 
Source data: Deutsche Gesellschaft fur Sonnenenergie e.V.
introduce it to the silicon. Where there is a boron 
atom, there is also a missing electron. This creates 
a “hole” in the outer shell of the boron atoms and 
its neighboring silicon atom (Figure 10-4). 
If we add a little bit of phosphorus to our silicon, 
we get the opposite effect, a “spare” electron 
(Figure 10-5), which doesn’t quite know where to 
fit in. As a result, it sort of “lingers uncomfortably” 
waiting for something to happen. 
Now, we can use these two types of “doped” 
silicon to make semiconducting devices, in this 
case “photovoltaic cells.” 
A photovoltaic solar cell is a bit like a sandwich. 
It is made from layers of different types of silicon, 
as illustrated in Figure 10-6. 
Starting from the base, we have a large contact. 
Then on top of this we have a layer of p-type 
silicon, a junction called the space charge region 
84 Solar Photovoltaics 
Figure 10-3 Plain old silicon—its atomic structure. 
Figure 10-4 Silicon doped with boron—note the 
missing electron. 
Figure 10-5 Silicon doped with phosphorus—note the 
spare electron. 
Figure 10-6 Cutaway solar cell.
where the magic occurs, and a slice of n-type 
silicon on top. 
On top of all this is layered a grid electrode, 
which does the job of making the other contact. 
Now, photons from the sun hit our solar cell, and 
in doing so “spare” negatively charged electrons, 
are “knocked” across the boundary between p- and 
n-silicon, which causes a flow of electrons around 
the circuit. 
We are now going to look at how the silicon 
for these solar cells is manufactured, using 
some things you can do at home. 
You will need 
. Plastic coffee jar (empty) 
. Skewer 
. Hardboiled egg 
. Sugar 
. Food coloring 
Tools 
. Compass 
. Egg slicer 
To make a photovoltaic cell we need silicon, this 
project is going to show you how solar cells are 
produced from crystalline silicon. The words 
“crystalline silicon” should indicate to you that 
this type of solar cell is made from crystals of 
silicon. We saw earlier how silicon aligns itself 
into a regular crystalline array, now we are going 
to look at growing this crystal. 
In industry, silicon crystals are grown to form a 
uniform cylinder of silicon which is used as the 
base material for crystalline solar cells. There is 
plenty of silicon about on the earth, in fact, as 
mentioned previously, after oxygen it is the second 
most abundant element. When you think that sand 
and quartz all contain silicon and then imagine the 
amount of sand in the world, you begin to realize 
that we are not going to run out of silicon in a 
hurry! 
The problem with sand is that it also contains 
oxygen in the form of silicon dioxide, which must 
be removed. 
The industrial process used to produce silicon 
requires temperatures of around 32708F (which is 
about 18008C). Obviously we can’t experiment 
with these sorts of temperatures at home—but we 
can recreate the process! 
If you don’t want to get the individual bits and 
bobs, a couple of educational scientific vendors 
sell rock-growing kits. These links are to suppliers 
of kits of parts: 
. scientificsonline.com/product.asp?pn=3039234& 
bhcd2=1151614245 
. www.sciencekit.com/category.asp_Q_c_E_737919 
. www.scienceartandmore.com/browseproducts/ 
Rock-Candy-Growing-Experiment-kit.html 
If you want to do it all yourself, then you can 
see from Figure 10-7 that the process is a relatively 
easy one! You are going to need a saturated sugar 
solution, this will sit in the lid of your coffee jar. 
Now, take a large crystal of sugar, often sold as 
“rock sugar” and “glue” it to the end of the skewer. 
Next, drill a hole the same diameter as the skewer, 
and poke the skewer through the bottom of the 
coffee jar. Stand it on a windowsill and lower the 
crystal into the saturated sugar solution. Over some 
Project 20: Grow Your Own “Silicon” Crystals 
85 
Project 20: Grow Your Own “Silicon” Crystals
time, crystals should start to grow—pull the 
skewer up slowly, bit by bit, so that the growing 
crystal is still in contact with the sugar solution. 
This is just like the way that silicon is grown. The 
silicon is drawn up slowly from a bath of molten hot 
silicon (which is analogous to our saturated sugar 
solution). This is shown in Figure 10-8. 
Once this large crystal of silicon has been manufactured, 
it must be cut into slices to manufacture 
the solar cells. I like to think of this a bit like the 
way an egg is sliced to make sandwiches by an 
egg slicer—see the analogy in Figures 10-9 and 
10-10. 
“Slice and dope” your silicon 
crystals 
Slicing an egg with an egg slicer is much like the 
process that happens when a solar cell is manufactured. 
Each slice of silicon is then called a 
“wafer.” 
We now need to create a p–n junction in the 
wafer; to do this phosphorus is diffused into the 
surface of the silicon. Dip your egg into some food 
coloring or beetroot juice, and you will see that the 
juice covers one surface of the egg slice. Now, 
imagine that slice of egg were a solar cell, with the 
beetroot-soaked face pointing toward the light. 
Imagine an electrical contact on either side of the 
egg slice is connected to our circuit. The photons 
86 Project 20: Grow Your Own “Silicon” Crystals 
Figure 10-7 Growing sugar crystals. 
Figure 10-8 Growing silicon crystals. 
Figure 10-9 Slicing eggs. 
Figure 10-10 Slicing silicon.
hit the colored side, which is “doped” with phosphorus 
to produce some extra electrons. By giving 
these electrons additional energy from the photons, 
they are able to “jump” the gap, across to the 
“boron” doped silicon (the plain old egg) where 
they fill the “holes” where there are electrons 
missing from the atomic structure. With a steady 
stream of photons, hitting the cell, a heavy stream 
of electrons are encouraged to migrate across the 
p–n junction, then travel around the circuit doing 
useful work! 
Now these cells can be integrated into larger 
modules, or even arrays, to produce more power. 
Now we have looked at the technology of 
crystalline solar cells using silicon, let us turn our 
attention to thin-film solar cells. 
Project 21: Build Your Own “Thin-Film” Solar Cell 
You will need 
. Copper sheeting 
. Clear Plexiglas/Perspex/acrylic sheeting 
. Some thin wood strip 
. Copper wire 
. Duct tape 
Tools 
. Metal guillotine (optional) 
. Bandsaw (optional) 
. Tin snips 
. Electric ring hob 
First of all, cut a square of the copper sheeting so 
that it is about 6–8 in. square in size. It is 
much easier to do this with a metal guillotine 
(Figure 10-12); however, if you haven’t got 
access to this sort of equipment, tin snips will 
work just fine. 
When you have done this, wash your hands 
thoroughly and dry them. You need to remove any 
grease or oil from your hands that could cause 
problems with the next step of the process. Remove 
any grease or detritus from the copper sheeting. Next, 
take a piece of emery cloth (see Figure 10-13), and 
thoroughly sand down the piece of copper on both 
sides to remove the top layer of oxidized copper.
87 
Project 21: Build Your Own “Thin-Film” Solar Cell 
Note 
First of all a little disclaimer ... the solar cell you 
are about to build here is horribly, horribly 
inefficient. Please do not have any plans to use 
these to power your home. The amount of current 
that they produce is very small and not economically 
exploitable. While this is a shame, this 
project is very interesting, educational and helps 
you get to grips with the photoelectric effect. 
Figure 10-11 Doping with phosphorus.
This will leave you with nice bright shiny red 
copper underneath. 
You now need to heat treat the copper, in order 
to form an oxide coating on top. It may sound 
counterintuitive that we have just removed all the 
oxide and now we are going to put oxide back on, 
but the oxide coating we will be applying will be a 
film of “cuprous oxide.” 
You will need an electric hob to do this. If you 
have any “heat proof gloves” and metal tongs, this 
might be the time to get them in order to handle 
the metal while hot. 
You need to turn the burner to the highest 
setting, with the sheet of copper just placed on top. 
Observe the changes to the copper carefully, they 
are very interesting. 
As you heat the copper, it takes on a lovely vivid 
patina of different colors. Obviously, the pages 
here are black and white, so I can’t show you, but 
if you look at Figure 10-14 a–e you will see the 
changes that the plate goes through. 
88 Project 21: Build Your Own “Thin-Film” Solar Cell 
Figure 10-12 Cutting the copper with a guillotine. 
Figure 10-13 Cleaning the copper with emery cloth.
You will see a black crusty oxide form on top of 
the copper plate. If you leave the plate to cool 
slowly, the crusty layer should become fairly 
fragile and separate easily from the underlying 
copper. When you have allowed the plate to cool 
thoroughly, give the plate a firm bang edge-on to a 
hard surface. Some of the oxide will pop off. Rub 
the oxide gently with your fingers under a tap, and 
you will find most of the black layer of oxide 
comes off easily. If any bits are stubborn, do not 
under any circumstances scour them, as we do not 
want to damage the fragile surface. 
Under this black layer of oxide, you will find 
another layer of a reddish orange rust color. This is 
the layer which is “photosensitive” and will make 
our thin-film solar cell work. 
Make a spacer now from some thin strips of 
wood (Figure 10-15). I used duct tape to join my 
pieces of wood together—do not use metal fixings 
as they could react electrolytically with the other 
components of the cell. 
We are now going to make another electrode. It 
has to have the property that it does not touch the 
89 
Project 21: Build Your Own “Thin-Film” Solar Cell 
Figure 10-14 The shiny copper plate on the burner. 
Hint 
If you have access to nitric acid, you can use this 
as a superior method for removing the upper 
cupric oxide layer.
other piece of the solar cell, and allows light to hit 
the surface. We are going to use salt water as our 
other electrode, making contact with the whole 
surface of the thin film cell, yet conducting electricity. 
We are then going to immerse another copper 
wire to make the connection. You could equally 
use another piece of copper plate around the outside 
of the thin-film cell, but not touching our oxidized 
copper. 
In a commercial thin-film cell, tin oxide is commonly 
used as the other electrode, as it is clear and 
yet conducts electricity. 
Now take a piece of Perspex to act as a cover 
plate, and stick a strip of duct tape on either side, 
as shown in Figure 10-16. 
We are going to stick our other electrode wire to 
this piece of Perspex. 
In Figure 10-17, I have used thickish wire for 
clarity, with few actual zigzags so that you can 
clearly see what is going on. To optimize the 
performance of your solar cell, you want to make 
the conductor large. To this end, you are better 
using lots of thinner gauge wire in a much finer 
zigzag pattern—this will still allow the light to get 
through, but at the same time gives a large 
conductor area. 
You can experiment with different types of wire 
and copper—the trick is to try and maximize the 
surface area of the copper, while trying to block as 
little light as possible from reaching the solar cell. 
Fold the duct tape over and stick the wire to 
the plate. 
We are now going to combine the electrode plate 
with the space. Again, duct tape makes this a nice 
easy job (Figure 10-18). 
Next, we are going to take the copper plate, and 
stick duct tape to one side, with the sticky side of 
the tape facing the same direction as the layer of 
red copper oxide (Figure 10-19). 
90 Project 21: Build Your Own “Thin-Film” Solar Cell 
Figure 10-15 The spacer piece. 
Figure 10-16 Perspex and duct tape. 
Figure 10-17 Wire electrode.
Combine the plate and the front module to make 
the finished solar cell (Figure 10-20). 
Now, take a little salt water, and fill the void 
between the Perspex front section and the copper 
plate. Seal the module with duct tape all round to 
prevent leakage. 
Finally, connect your module to a multimeter, 
find a bright light source, and explore some of the 
electrical properties of your solar cell. 
Experiments with 
photovoltaic cells 
In this project we will be performing a range of 
experiments with photovoltaic cells that allow us 
to learn something about their characteristics and 
how they perform in different applications. 
The experiments in this project could form 
a great basis of a science fair stand or poster 
display. 
91 
Project 21: Build Your Own “Thin-Film” Solar Cell 
Figure 10-18 Perspex plate and electrode combined. 
Figure 10-19 The copper plate with duct tape fixings. 
Figure 10-20 The finished solar cell. 
Chemical data file: cuprous 
oxide 
Cuprous oxide (red) 
Formula Cu2O 
Molecular weight 143.08 
Physical appearance Red to reddish brown 
powder
Project 22: Experimenting with the Current–Voltage 
Characteristics of a Solar Cell 
You will need 
. Light source 
. Photovoltaic cell 
. Voltmeter 
. Ammeter 
. Variable resistance 
. Graph paper and pencil 
or 
. Computer with spreadsheet package 
We can learn a lot about solar cells’ electrical 
characteristics by plotting the “current–voltage” 
curve of the device. 
To carry out the experiment, we will need to 
ensure that the solar cell receives constant illumination 
all the time. Use a bright lamp, and position 
it a fixed distance above the solar cell. 
Set up the circuit as shown in Figure 10-21. 
We are now going to adjust the variable resistor 
from one extreme to the other, noting how the 
readings on the voltmeter and ammeter change as 
we do so. At this point you need to make careful 
notes as to the current and the voltage at each 
stage. You can do this on paper, or, if you have a 
PC handy, on a spreadsheet. Try and take at least 
15 or so different readings to help you plot an 
accurate curve. 
Now plot the points on your graph paper, or by 
using the chart wizard on a spreadsheet program. 
Compare your graph to Figure 10-22. The graph 
tells us how the solar cell will perform when 
different loads are applied. 
92 Project 22: Current–Voltage Characteristics 
Figure 10-21 Circuit to determine the current–voltage 
curve of a single solar cell. 
Figure 10-22 Current–voltage characteristics of 
a single solar cell.
Project 23: Experimenting with Current–Voltage 
Characteristics of Solar Cells in Series 
Project 24: Experimenting with Solar Cells in Parallel 
You will need 
. Light source 
. Three photovoltaic cells 
. Voltmeter 
. Ammeter 
. Variable resistance 
. Graph paper and pencil 
or 
. Computer with spreadsheet package 
You will need 
. Light source 
. Three photovoltaic cells 
. Voltmeter 
. Ammeter 
. Variable resistance 
. Graph paper and pencil 
or 
. Computer with spreadsheet package 
Now we are going to repeat the experiment above, 
but we are going to do it three times. 
Set up the circuit as shown in Figure 10-23. First 
using one cell, then two, then three. 
You can reuse your result for above for the 
single solar cell, but we are now going to add two 
additional lines to our graph—one for two solar 
cells connected in series, and another for three 
solar cells in series. 
What can we see from the results (Figure 10-24)? 
Well, it is clear that when we add multiple solar 
cells in series, the voltages “add up.” However, the 
current produced remains the same. 
93 
Project 24: Experimenting with Solar Cells 
Figure 10-23 Circuit to determine the 
current–voltage curve of solar cells in series. 
Figure 10-24 Current–voltage curve of solar cells 
connected in series.
We are now going to connect solar cells in parallel 
and repeat the experiment. 
Again, we will end up with a graph with three 
lines. Make a prediction now! How do you expect 
this graph to differ from the one when we 
connected solar cells in series? 
The solar cells will be connected in accordance 
with Figure 10-25. First connect one cell, then two 
in parallel, then three! 
Now plot the graph from the points that you 
obtained (Figure 10-26) and compare it to 
Figure 10-24. 
How do the two graphs differ? Well, it can be 
seen that in the parallel plots, the voltage remains 
the same throughout, and it is the current that 
changes—contrast this to the series experiment 
where it was the voltage that changed. 
94 Project 25: The “Inverse Square Law” 
Figure 10-25 Circuit to determine the 
current–voltage curve of solar cells in parallel. 
Figure 10-26 Current–voltage curve of solar cells 
connected in parallel. 
Project 25: Experiment with the “Inverse Square Law” 
You will need 
. Light source 
. Photovoltaic cell 
. Voltmeter 
. Ammeter 
. Variable resistance 
. Graph paper and pencil 
or 
. Computer with spreadsheet package 
The inverse square law says that for each unit of 
distance you move a light away from a solar cell, 
the amount of received light is equal to the inverse 
of the square of that distance (Figure 10-27). 
As we are trying to measure the light only from 
a point source, it is a good idea if you can try and 
do this in a darkened room. 
Take a single solar cell, and connect a voltmeter 
and ammeter across its terminals. We are going to 
move the light away and measure the voltage and 
the current produced. Remember, it is easy to find 
the total “power” produced by multiplying the 
voltage and the current together. Compare the 
power generated, to the distance that the light 
source is from the solar cell. Plot this in a copy of 
Table 10-2. What do we learn about the
relationship between the light falling on the cell 
and the power generated? 
Our solar cell produces more power when there 
is more light falling on it. We can repeat the 
experiment for a current–voltage curve, with 
different amounts of light falling on the solar cell. 
What we learn is that the current–voltage 
curve of the cell changes depending on the 
amount of light falling on it. This can be seen in 
Figure 10-28. 
95 
Project 25: The “Inverse Square Law” 
Figure 10-27 Inverse square law. 
Figure 10-28 How the current–voltage curve of the 
solar cell changes with varying illuminance. 
Table 10-2 
Measuring power produced by a solar cell 
when light is held at different distances 
Distance Distance Load Short circuit 
(in.) (cm) voltage (V) current (mA) 
0 0 
2 5 
4 10 
6 15 
8 20 
10 25 
12 30 
14 35 
16 40 
18 45 
20 50
Project 26: Experimenting with Different Types 
of Light Sources 
Project 27: Experimenting with Direct 
and Diffuse Radiation 
You will need 
. Light source 
. Photovoltaic cell 
. Voltmeter 
. Ammeter 
. Variable resistance 
. Paper to shade 
The concept that we are going to get to grips with 
in this experiment is that reflected light can 
produce an awful lot of illumination and hence 
energy. 
Look at the two types of radiation hitting the 
solar cell in Figure 10-29. Now, using the techniques 
shown in Figures 10-30 and 10-31, shade 
the solar cell from either direct or indirect 
radiation and note the amount of power that is 
produced. 
You will need 
. Light source 
. Photovoltaic cell 
. Voltmeter 
. Ammeter 
. Variable resistance 
In this experiment we are going to look at the 
range of values for power produced from different 
light sources. Take your solar cell, and connect it 
in the same manner as when we measured current– 
voltage curves, and try different sources of light. 
Plot the results in a copy of Table 10-3. How does 
the power generated compare with natural light? 
96 Project 27: Direct and Diffuse Radiation 
Table 10-3 
Measuring power produced by a solar cell 
with different light sources 
Type of light Load voltage (V) Current (mA) 
Sunlight (sunny day) 
Sunlight (dull day) 
Sunlight (overcast day) 
Incandescent lamp 
Compact fluorescent 
lamp 
Fluorescent lamp 
Ultraviolet lamp 
Orange sodium street 
light
How does the amount of power produced from 
indirect radiation compare to that from direct 
radiation? There are solar cells available called 
“bifacial solar cells” (Figure 10-32). 
These solar cells are mounted on a clear substrate 
to form a module. They have the advantage 
that they can collect light from both sides, so 
they can absorb direct and indirect radiation. 
This means that they can absorb more power than 
had they just been collecting light from one 
direction. 
In Figure 10-33, they have been mounted on the 
roof of a covered walkway. In this application, the 
solar cells are serving two purposes—generating 
clean energy, while keeping the rain off people 
walking along the walkway. 
97 
Project 27: Direct and Diffuse Radiation Figure 10-29 Radiation hitting a solar cell. 
Figure 10-30 Blocking indirect radiation. Figure 10-31 Blocking direct radiation.
98 Project 27: Direct and Diffuse Radiation 
Figure 10-32 Bifacial solar cells. 
Figure 10-33 Bifacial solar cells on the roof of a covered walkway.
Project 28: Measurement of “Albedo Radiation” 
You will need 
. Light source 
. Photovoltaic cell 
. Voltmeter 
. Ammeter 
. Variable resistance 
. Paper to shade 
What is albedo radiation? 
The ground is a surface just like any other, it has 
the capability to reflect radiation so we must not 
ignore it. Just think, black tarmac is bound to 
reflect less radiation than say a light gray concrete. 
Why are we bothered—our solar cells point 
toward the sky don’t they? 
Well, yes, that is true in most cases; however, 
bifacial solar cells are able to accept solar radiation 
on both faces. 
The experiment 
The next experiment may seem counterintuitive, 
but it is very worthwhile. We are going to be 
measuring albedo radiation. Using your solar 
setup, point your PV panel at the floor and take a 
measurement (Figure 10-34). 
What did you expect? A zero reading? In fact, 
as you can see, there is still a lot of energy in 
“indirect” radiation which is reflected from other 
surfaces. We saw in the last experiment how 
bifacial solar cells are able to collect the solar 
energy reflected from two faces. Therefore, in the 
covered walkway they can collect energy reflected 
from the ground (albedo) as well as from direct 
radiation. 
Applications of 
photovoltaic cells 
We have explored some of the properties of individual 
photovoltaic cells and seen how light can be 
used to produce electricity, now let’s look at some 
applications of solar cells. 
First of all, despite electricity from solar cells 
currently costing much more than power from the 
grid, solar cells can be useful for applications where 
there is not a nearby electricity supply, and where 
a connection to the grid could potentially be quite 
expensive. 
We saw earlier, how the first solar cells were 
used to power satellites in space (Figure 10-35), 
where other forms of power were impractical. 
Figure 10-36 shows a road sign in the English 
countryside, the black sign above is an illuminated 
display, which lights up when drivers go too fast. 
It is lit by power produced during the day from a 
solar cell and also from a micro wind turbine at
99 
Project 28: Measurement of “Albedo Radiation” 
Figure 10-34 Measuring albedo radiation.
day or night. The power is stored locally in 
batteries located in the foundation of the sign. 
In addition to powering devices in remote locations 
with no access to the power grid, we can also 
construct large photovoltaic arrays, which generate 
a significant quantity of electricity which can be 
“fed into” the grid when it is not being used onsite. 
The great thing about photovoltaic cells, is 
that they can be used in place of things like roof 
tiles and shingles—so although we cover the building 
with photovoltaic cells, which are expensive, we 
save on the cost of the roofing material. 
We can see how a solar array can be made plain 
and large as in this solar array at the Centre for 
Alternative Technology, U.K. (Figure 10-37). 
Or with a little bit of thought, they can be 
integrated creatively into the building fabric as 
shown in Figure 10-38. 
What does it take to 
solar power my home? 
Producing electricity by photovoltaic cells is fairly 
expensive compared to other types of generation. 
However, when considering the “cost” of solar 
energy, figure in all of the carbon emissions that 
you aren’t producing, and the toxic waste that you 
aren’t making. 
We now know that solar cells can be used to 
generate electricity, but the problem is getting it in 
a form that we can use in our homes. Sure, it is 
possible to run a few simple bulbs from a DC 
supply, but to run most of our household appliances, 
we need to generate electricity in a form that is 
suitable for them—AC. 
You will notice that the output from all of our 
solar cells is “direct current” (see Figure 10-39). 
The voltage is always a fixed polarity with reference 
to 0 V. We can couple solar cells in series to 
produce a higher voltage, or in parallel to produce 
100 Solar Power for Your Home 
Figure 10-35 The HEESI satellite powered by solar 
power. Image courtesy NASA. 
Figure 10-36 A road sign powered by renewable 
energy.
101 
Solar Power for Your Home 
Figure 10-37 The 11 kW solar array at the Centre for Alternative Technology, U.K. 
Figure 10-38 Photovoltaic cells creatively integrated into a building fabric. Image courtesy Jason Hawkes.
a higher current, but we are always going to end 
up with DC. 
By contrast, in our homes, our appliances and 
devices require “alternating current,” AC (Figure 
10-40). We see how the AC waveform differs 
dramatically from the steady DC line. In the 
United States, the frequency of this AC supply is 
60 Hz, in the U.K. it is 50 Hz, it is also at a higher 
voltage (120 V in the U.S.A., and 230 V in the U.K.). 
So, how can we take the power from our photovoltaic 
cells, and turn it from “DC low voltage” 
into “AC high voltage”? The answer is that we use 
an “inverter.” 
An inverter is a piece of electronics (Figure 10-41), 
which takes the DC supply from our solar cell 
and generates an AC waveform at the correct 
voltage and frequency for our items of mains 
equipment. 
We need some extra devices for safety reasons, 
you will see in the setup that there is a mains 
isolator switch (as shown in Figure 10-42). This 
allows us to disconnect the mains from the inverter 
102 Solar Power for Your Home 
Figure 10-39 Direct current. Figure 10-40 Alternating current. 
Figure 10-41 A typical inverter setup.
in the event that we need to carry out work or 
maintenance. 
We also need to include a mains circuit breaker 
to protect against overcurrents or surges, which 
could be potentially damaging and dangerous. 
A circuit breaker is shown in Figure 10-43. 
And in addition, we need to be able to isolate 
the DC supply coming from our solar array. A DC 
isolator switch is shown in Figure 10-44. 
It is also interesting to see how much energy our 
solar array is producing. This can be useful for 
accounting purposes, say if we are selling the solar 
energy back to the grid, or simply to benchmark 
the performance of our solar system and see if it is 
in line with our design predictions. A watt hour 
meter is shown in Figure 10-45. 
103 
Solar Power for Your Home
Figure 10-42 Mains isolator switch. Figure 10-43 Mains circuit breaker. 
Figure 10-44 Solar DC isolator switch.
104 Solar Power for Your Home 
Figure 10-45 Watt hour meter. Figure 10-46 Awelamentawe school solar display. 
Image courtesy Dulas. 
Of course, if we have a solar array in a public 
area, it is also nice to promote solar technology to 
others, and our solar array is a powerful tool to 
educate others with. At this school in Wales, in 
Awelamentawe (Figure 10-46), a display is 
prominently mounted in the main reception, to 
show visitors, and help educate children about, 
how much energy the school’s solar array is 
producing.
Photochemical Solar Cells 
Chapter 11 
My sincerest thanks to Dr. Greg P. Smestad for the 
information and images he has provided, on which 
this chapter is based. 
In addition to the photovoltaic solar cells that 
we have seen earlier in this book, there are other 
ways of generating electricity directly from the 
sun. We saw how photovoltaic solar cells rely on 
the photovoltaic effect that occurs at semiconductor 
junctions, and how the semiconductor performs the 
two jobs of absorbing the light and separating 
electrons. 
One of the problems with this approach is that, 
because of the sensitive nature of the cells, they 
must be manufactured in ultra-clean conditions in 
order to be clean and free from defects which 
might impede their operation. 
This works effectively; however, it is expensive. 
The thing about photochemical solar cells is 
that they use cheap technology. Titanium dioxide 
is not some rare chemical that requires expensive 
processing, it is already produced in large quantities 
and used commonly; furthermore, you don’t 
need an awful lot of it—only around 10 g per 
square meter. When you figure that this 10 g only 
costs two cents, you begin to realize that this is a 
solar technology with a lot of promise for the 
future. 
In an attempt to make solar technology cheaper 
and more accessible, Michael Grätzel and Brian 
O’Regan from the Swiss Federal Institute of 
Technology decided to explore different approaches 
to the problem. 
The photochemical solar cell has grown out of 
an expanding branch of technology—biomimickry, 
looking at how we can mimic natural processes to 
make more advanced technologies. 
Rather than having a single thing to do all of the 
jobs, as in a conventional photovoltaic cell, 
photochemical solar cells mimic processes that 
occur in nature. 
Electron transfer is the foundation for all life in 
cells; it occurs in the mitochondria, the powerhouses 
of cells which convert nutrients into energy. 
Titanium dioxide, while not immediately 
springing to mind as a household name, is 
incorporated in a lot of the products that we use 
every day. In paints, as a pigment, it is known by 
its name titanium white. It is also used in products 
such as toothpaste and sunscreen. Titanium dioxide 
is great at absorbing ultraviolet light. 
105 
Tip 
You might find titanium dioxide referred to as 
“Titania” in some references. 
Note 
The photochemical solar cell is sometimes also 
referred to as the “Grätzel” cell after Michael 
Grätzel who worked on developing the cell. 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
106 
How do photochemical 
solar cells work? 
Take a peek at Figure 11-1, in the top image, we 
can see the energy transfers taking place—the 
light striking our photochemical solar cell, 
generating energy and turning the shaft of the 
electric motor, which is connected to our cell. 
The radiated energy from the sun in the form of 
light, is being transformed through a chemical 
process into electrical energy, which travels 
through the circuit to the motor, where electromagnets 
turn the electrical energy into movement 
(kinetic energy). 
We need to look at the cell in a little more 
depth to understand the chemical processes that 
are taking place in it in order to generate the 
electricity. 
The dye when it is excited by light injects an 
electron into the titanium dioxide with which the 
plates are coated and semiconducts. 
Photochemical Solar Cells 
Figure 11-1 How a photochemical solar cell works. Image courtesy Greg P. Smestad.
Project 29: Build Your Own Photochemical Solar Cell 
You will need 
. Berries 
. Motor 
. Alligator clips 
. Wires 
. Nanocrystalline TiO2 Degussa P25 powder in 
mortar and pestle 
. Glass plates 
Tools 
. Petri dishes 
. Tweezers 
. Pipette 
. Pencil 
We need to get our titanium dioxide ground 
down so that the particles are as small as possible—
this maximizes surface area, and so allows 
our reactions to take place quickly. To do this, 
we will need the mortar and pestle mentioned 
in our “tools” list (Figure 11-2). Be careful not 
to inhale any of the fine titanium dioxide powder 
as you are grinding, as it won’t do you any good! 
Now that we have prepared our suspension of 
titanium dioxide, we need to coat it onto our glass 
plate using a glass rod. This is shown in Figure 11-3. 
The next thing that we need to do is sinter the 
titanium dioxide film in order to reduce its 
resistivity. This is shown in Figure 11-4. To do 
this, we hold it in a Bunsen flame and allow the 
gas to do the work! We need to hold the plate at 
the tip of the flame where the temperature is 
approximately 450°C or 842°F. 
Hold it steady for around 10–15 minutes. 
Now you need to produce the dye which will 
sensitize our photochemical solar cell. There are 
107 
Project 29: Build a Photochemical Solar Cell 
Online resources 
Point your browser toward 
www.solideas.com/solrcell/cellkit.html 
for more information on dye sensitized 
photochemical solar cells and where you can 
obtain a kit of the parts featured in this project. 
Figure 11-2 Grinding the nanocrystalline titanium 
dioxide. Image courtesy Greg P. Smestad. 
Figure 11-3 Using a glass rod to spread the suspension 
onto the plate. Image courtesy Greg P. Smestad.
a number of suggestions for different substances 
which can be used for this cell. You can try: 
. Blackberries 
. Raspberries 
. Pomegranate seeds 
. Red hibiscus tea in a few ml of water 
To produce the dye, you need to take the substance 
you are going to make the dye from, and crush it in a 
small saucer or dish. Once this has been done and a 
nice fluid has been produced, take the plate which 
has been coated in titanium dioxide, and immerse it 
in the dye. The titanium dioxide film should now be 
stained a deep red to purple color and the color 
distribution should be nice and even. If this is not the 
case, you can immerse the plate in the dye again. 
Once you have finished staining the plate, take a little 
ethanol and wash the film and then with a tissue, blot 
the plate dry. This is illustrated in Figure 11-5. 
Now we need to prepare the other electrode. To 
do this you will need another of the coated glass 
plates (the one with the conductive tin oxide 
coating—not the one with a titanium dioxide 
coating). You need to find which is the conductive 
surface. There are two ways of doing this—the 
tactile method is to simply rub the plate. It should 
feel rougher on the coated side. The other involves 
a voltmeter or continuity tester. The conductive 
side is the one which yields a positive reading 
when tested for continuity. 
We now need to deposit a layer of graphite. The 
easiest way to do this is take a soft pencil, and 
simply scribble on the surface until a nice even 
coating of graphite is obtained. This is shown in 
Figure 11-6. Just note that you need to do this with 
a plain pencil not a colored one! 
Now if you have got this far, you are on the 
home run! The next thing we need to do is take 
some of the iodine/iodide mixture, and spread a 
few drops evenly on the plate that was stained with 
the dye (Figure 11-7). Once you have done this, 
108 Project 29: Build a Photochemical Solar Cell 
Figure 11-4 Firing the film of titanium dioxide in 
order to sinter it. Image courtesy Greg P. Smestad. 
Figure 11-6 Applying a graphite film to one electrode. 
Image courtesy Greg P. Smestad. 
Figure 11-5 Coating the plate in berry juice. Image 
courtesy Greg P. Smestad.
take the other electrode and place it on top of the 
dyed electrode. Stagger the junction between the 
two plates in order that you leave a little of each 
exposed at either end—you can then use a couple of 
crocodile clips to connect the cell to a multimeter. 
Now clip the sheets of glass together carefully to 
ensure they stay together (Figure 11-8). 
Now connect a multimeter—we can start to 
think about doing some really cool stuff now! You 
might like to try a few different experiments—like 
seeing what way to shine the light through the cell 
for the most effective operation. You might like to 
repeat some of the experiments in the section on 
photovoltaic solar cells, and see what results you 
obtain with a photochemical solar cell. 
Another educational idea is to use a multimeter 
to measure the amount of power from both a 
photovoltaic solar cell, and the photochemical 
solar cell you have made, and compare the 
results—now work out their relative efficiencies 
taking into account the area of the cells. 
Now we can take some measurements! Figure 11-9 
shows a photochemical cell yielding 6.0 mA! 
Apparently, the juice in this picture is from 
Californian blackberries! 
Figure 11-10 shows a photochemical cell being 
used to drive a small motor and fan. 
109 
Project 29: Build a Photochemical Solar Cell Figure 11-7 Applying the iodine/iodide mixture. Image 
courtesy Greg P. Smestad. 
Figure 11-8 Clipping the cell together with bulldog 
clips. Image courtesy Greg P. Smestad. 
Figure 11-9 The cell yields 6.0 mA. Image courtesy 
Greg P. Smestad. 
Figure 11-10 The cell driving a small motor. Image 
courtesy Greg P. Smestad.
Figure 11-11 shows a close-up of the cell 
working in action! 
Where does it all go from 
here? 
This technology has a lot of promise for the future. 
There is a growing trend for manufacturers to integrate 
renewable energy systems into building elements—
this allows us to feed two birds with one 
crumb, rather than shelling out for roof tiles and 
solar cells, why not buy a solar roof tile! The exciting 
thing about photochemical solar cells is that 
unlike photovoltaic cells, they don’t necessarily 
have to be opaque. This opens up exciting possibilities—
shaded windows and skylights which 
simultaneously produce electricity. How cool 
would that be! 
When you consider all of the glazing that adorns 
the skyscrapers in our cities, you begin to realize 
that this technology has interesting applications 
for energy generation. It also allows us to make 
good use of daylight with our south-facing 
building areas, while generating energy at the 
same time. 
There are also implications for consumer electronics, 
the watch giant Swatch has already built a 
prototype watch with a photochemical cover glass. 
This allows the glass which covers the watch to 
generate electricity all the time the watch is 
exposed to light. When you think that people wear 
watches on their wrists where they are permanently 
exposed to daylight, this becomes quite a sound 
idea! Of course, you also need some means of 
storing the electricity to enable the watch to run 
at night! It would be no good to wake up, put on 
your watch, only to find the time is set to the 
evening before. 
Are there any limitations 
to this technology? 
One of the problems with this particular type of 
cell is that the cell contains liquid which is 
essential for its function. Unfortunately, liquid is 
hard to seal and keep in—preventing the liquid 
from leaking is a real technical issue that needs to 
be solved. After all, you wouldn’t want leaky 
windows! If you have ever seen a poorly fitted 
double glazing panel with condensation inside, 
you realize how hard it is to seal building 
fixtures and fittings against the ingress or egress 
of fluid. 
However, there is hope on the horizon, Grätzel 
together with the Hoescht Research & Technology 
in Frankfurt, Germany, and the Max Planck Institute 
for Polymer Research in Mainz, Germany, have 
announced that they have developed a version of 
the cell with a solid electrolyte; however, efficiencies 
are low. 
110 Project 29: Build a Photochemical Solar Cell 
Figure 11-11 A closeup of the photochemical cell in 
action. Image courtesy Greg P. Smestad. 
Online resources 
The materials required for this project are 
available from the Institute of Chemical 
Education from the following link or the address 
in the Supplier’s Index: ice.chem.wisc.edu/ 
catalogitems/ScienceKits.htm#SolarCell
Photobiological solar 
cells? 
Truth can sometimes be stranger than fiction. 
Realizing that conventional solar cells require 
expensive industrial processes, researchers at 
Arizona State University have initiated a project 
codenamed Project Ingenhousz which is looking 
at photosynthesis and how organisms can be used 
to harness solar energy to produce fuels that will 
wean us away from our carbon-based fossil fuels. 
Could your car one day run from hydrogen that 
has been produced by algae from solar energy?
111 
Photobiological Solar Cells
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Solar Engines 
Chapter 12 
In this book so far, we have seen how it is possible 
to utilize the energy that comes from the 
sun in order to do some really useful things. While 
generating heat and electricity is useful to help us 
reduce our energy consumption, it would also be 
useful if we could use the sun’s energy to create 
mechanical movement. Mechanical movement is 
very useful and can be directly utilized to drive 
machinery. 
When we look at the type of energy coming 
from the sun, we can see that it is heat and light— 
the energy is transmitted by radiation through the 
vacuum of space. 
How therefore, do we exploit this radiated 
energy and convert it into mechanical motion? 
You must be familiar with the steam engines that 
once graced railways throughout the world. The 
steam engine is a form of indirect combustion 
engine, the coal is burned to heat water, which 
undergoes a phase change—the water turns from 
liquid to gas. In doing so, it increases in volume— 
what once took up a small space, now takes up a 
large space—this change can be exploited to 
provide mechanical movement by driving a piston. 
Furthermore, the change in volume when hot 
steam condenses back to water can also be used to 
provide movement. 
If you want proof of this, take a soda can with a 
little bit of water in the bottom. Heat it on the 
stove until you see a little wisp of water vapor 
come from the can—this is evidence of the water 
having boiled. Now, using tongs, flip the can over, 
and immerse the “top” of the can in a bowl of ice 
cold water. The can is instantly crushed! 
So now we have evidence that a change in 
temperature can produce movement, we can look 
at how to harness this raw power. 
The engines described in this chapter, are all 
examples of thermodynamic heat engines. The 
chapter will showcase a few simple solar engines 
that you can construct yourself with relatively 
simple materials. 
All of the engines in this chapter produce a 
fairly modest amount of mechanical power, but all 
serve to demonstrate that solar energy does have 
application in directly driving mechanical devices. 
I gratefully acknowledge the advice and 
guidance of Hubert Stierhof in the preparation of a 
number of projects in this chapter. 
You will need 
. Happy Drinking Bird (won’t be so happy when we 
are finished!) 
. Silver spray paint 
. Black spray paint 
Tools 
. Scalpel 
. Kettle 
We are going to have to “kill a bird” to execute 
this project—luckily the bird in question is 
Project 30: Build a Solar Bird Engine 
113 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
a cheap toy from the Far East, so our consciences 
are clear! 
The “Happy Bird,” “Happy Drinking Bird,” 
“Drinking Bird,” “Tippy Bird,” “Sippy Bird,” 
“Dippy Bird” or any one of a number of ridiculous 
names is a cheap novelty toy (Figure 12-1). It is 
also a serious scientific curiosity! 
First of all a little note, don’t jump straight into 
massacring the bird—have a little play with it, 
because it is a lot easier to see what is going on 
before you hack it (Figure 12-2). 
How the Drinking Bird works 
The Drinking Bird contains a pair of glass bulbs, 
joined by a glass tube, attached to which is a pivot. 
The pivot rests on top of the “legs” of the bird, and 
in the normal position, one bulb (the tail) will be 
full of liquid, while the other bulb (the head) will 
be empty. 
The liquid inside the bird (dichloromethane) 
condenses readily with only a small temperature 
difference. In the normal mode of operation, you 
start the bird by “dunking” its head in a small glass 
of water, and then allowing it to stand. What 
happens when you do this, is that water begins to 
evaporate from the bird’s head. As it does so, it 
takes heat with it, cooling the bird’s head, relative 
to the ambient temperature, which the “bottom” 
bulb is at. 
As the top is cooled, the dichloromethane gas in 
the head begins to condense creating a drop in 
pressure. The liquid from the bottom bulb now 
begins to flow into the head bulb. 
As the liquid moves through the central tube, 
the weight distribution of the liquid in the bird 
changes. The bird now becomes “top heavy” and 
as a result of this, the bird rotates on its pivot. This 
movement is the useful “work” which the heat 
engine is doing. 
114 Project 30: Build a Solar Bird Engine 
Figure 12-1 The Drinking Bird in its box. 
Figure 12-2 The Drinking Bird in action. 
Warning 
The liquid which fills the Drinking Bird is known 
as dichloromethane. This chemical is pretty nasty 
stuff—safe while trapped in the glass of the 
drinking bird’s body, but nasty if it escapes—so 
exercise caution, and try not to break or damage 
the bird in any way.
As the bird tips over, the seal between the “neck” 
tube, and the surface of the dichloromethane is 
broken. A small bubble of vapor flows through the 
neck tubes. As it does so, it displaces liquid, which 
begins to flow back down to the tail bulb. As the 
liquid flows back from top to bottom, the vapor 
pressure equalizes and the bird “rights itself.” 
As the liquid flows back into the bottom bulb, 
the weight distribution again changes, and the bird 
pivots back to its vertical position. Again, more 
useful “work” is done here. 
The cycle keeps repeating itself until the water 
in the pot runs out. The process is driven by the 
heat in the environment which causes the water to 
evaporate. The dichloromethane is not “used up” in 
any way—it is the working fluid of the engine and 
stays trapped inside the drinking bird. 
We are going to change the Drinking Bird, so 
that instead of being driven by the temperature 
difference caused by water evaporating, it will 
instead be driven by the temperature difference 
created by surfaces that absorb and reflect the 
sun’s rays. 
How we are going to “hack” it . . . 
We don’t want to have to keep replacing our water 
in order to keep the bird working. 
Now is the fun part, if you are of a destructive 
disposition. 
We are going to take all of the little accoutrements 
away from this beasty! Boil a kettle and 
get some hot water, you will find it softens the 
glue and makes it a lot easier to remove things. 
Remember, the glass is only thin and easy to 
break. 
Pull the hat of the bird. The hat usually disguises 
a little glass protrusion on the top of the bulb 
(Figures 12-3 and 12-4), so do this carefully, if you 
break the envelope of the bird it stops working. 
Also, the little tail feather is going to need to go. 
Next you are going to have to remove the felt and 
nose from the head. With a sharp scalpel, you can 
cut through the plastic backing of the felt, and 
using hot water, you can scrape all the glue and 
gunk off. You should now be left with a nice clean 
piece of glassware. 
Now, remember that the device works on the 
principle of temperature difference. You will 
remember from experiments earlier in the book, 
that black surfaces absorb solar radiation, while 
shiny or reflective light surfaces reflect solar 
energy. A black car feels hotter than the silver one 
115 
Project 30: Build a Solar Bird Engine 
Figure 12-3 The drinking bird stripped bare. 
Figure 12-4 The “hacked” drinking bird with it's 
fresh new paint scheme.
next to it! So, get some spray paint—the type used 
for touching in dents on cars works well—and 
spray the bottom bulb black and the top one silver. 
Remember the evaporation of water cooling the 
“head” of the bird. Well, instead, reflective silver 
paint is going to keep the head cool. The black 
“base” of the bird is going to heat up as it absorbs 
solar radiation. 
Now position the “solar engine” back on the legs 
of the bird, and put it somewhere where it will 
receive a lot of sunlight. You should now see the 
engine tipping away without the need for any water! 
Project 31: Make a Radial Solar Can Engine 
You will need 
. Polystyrene ceiling tile or sheet polystyrene 
. Three old cans 
. Stiff wire (coat hanger wire is ideal) 
. Three balloons 
. Wooden strut 
Tools 
. Tin opener 
. Scissors 
. Wire snips 
You might remember the biplane engines of old— 
they had their pistons arranged around a centrally 
driven shaft—the prop shaft—which would turn 
the propeller. This is known as a radial engine. 
In our cars, the pistons are generally arranged in 
a straight line or sometimes a “V,” radial engines 
are different in this respect. 
In this project, we will be building a radial 
engine, only rather than being fueled by aviation 
fuel, our engine is powered by the sun! 
How does the solar radial engine 
work? 
The cans that are exposed to the sun (i.e. not 
covered by the polystyrene shield) heat up as a 
result of the black covering absorbing the sun’s 
rays. This increase in temperature results in the air 
inside the can expanding slightly. This increase in 
volume exerts a force on the rubber diaphragm 
covering the can. The diaphragm is connected to a 
short rod, which pushes against the crank turning 
the can assembly. When the can has rotated far 
enough so that it is covered by the polystyrene shade, 
then the sun’s rays can no longer reach the can. As 
a result, the air inside the can begins to cool down. 
As the air cools, it contracts, in doing so, it pulls 
the rubber diaphragm (Figures 12-5 to 12-12). 
116 Project 31: Make a Radial Solar Can Engine 
Figure 12-5 Solar radial can engine.
117 
Project 31: Make a Radial Solar Can Engine 
Figure 12-6 The polystyrene shade. 
Figure 12-7 The view from behind the can engine. 
Figure 12-8 The can assembly (note the crank 
detail!). 
Figure 12-9 The can assembly on its stand (from 
above). 
Figure 12-10 The can assembly on its stand (from 
the side).
118 Project 31: Make a Radial Solar Can Engine 
Figure 12-11 Note carefully how the crank is 
configured. 
Figure 12-12 Diagram of the radial can engine.
Solar Electrical Projects 
Chapter 13 
In this chapter, we cover a number of small 
electronic projects you can build that are powered 
by solar energy. The chapter aims to show you 
how many common household devices that we 
take for granted could potentially run successfully 
on solar energy. 
119 
Project 32: Build Your Own Solar Battery Charger 
You will need 
. AA battery holder 
. 9 V battery clip (you might need this to connect to 
your battery holder) 
. 8 × solar cells 0.5V, 20 to 50 mA in full sun 
. 1N5818 Schottky diode 
Rechargeable batteries make good economic and 
environmental sense. In the same way that you 
wouldn’t throw away the glass every time you had 
a drink, so it doesn’t make sense to dispose of 
batteries when others are available that perform the 
same task many times over. 
It gets even better than that when you realize 
that you don’t have to use any mains electricity at 
all to recharge your batteries—you can use the 
power of the sun! 
Solar battery chargers like this model are 
commercially available, which can be obtained 
from the Centre for Alternative Technology, U.K. 
(see Supplier’s Index) (Figure 13-1); however, if 
you are electronically minded you can easily put 
one together. 
The circuit here will recharge a pair of AA 
batteries quite happily when left in the sun. 
This circuit is a very simple design which doesn’t 
provide any regulation, so you will need to make 
sure that you disconnect your batteries when they 
are recharged. 
The Schottky diode prevents the batteries’ charge 
from flowing back through the solar cells when no 
charge is present. Schottky diodes have the advantage 
of not sapping too much of the power from 
our solar cells—maximizing the amount that is 
delivered to the batteries. 
The schematic for the battery charger is shown 
in Figure 13-2. 
Construction is fairly simple. There are a wide 
array of cases available that are suitable for 
housing such a project. If you can get a housing 
with an integral battery holder you will find it will 
make neat work of housing the project. 
Hint 
If you live in a climate where sun is a rare treat 
and it is often overcast, you might like to 
experiment with a couple of additional cells in 
series to increase the power produced. 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
120 Project 33: Build Your Own Solar Phone Charger 
Figure 13-2 Solar battery charger schematic. 
Figure 13-1 Commercially available solar battery 
charger. 
Tip 
House the cells in such a manner that they are 
shaded and protected from the sun. If the cells get 
too hot their electrolyte leaks—damaging the cell 
and making a mess. 
If you want to build a “deluxe” model, you 
might want to consider incorporating a small 
milliammeter to monitor the charging status. 
Project 33: Build Your Own Solar Phone Charger 
You will need 
. Car charger suitable for your cell phone (for 
cannibalization) 
. 7812 voltage regulator 
. 15 V solar array 
Or for the USB version: 
. 100 µF capacitor 
. 100 pF capacitor 
. 1 mH inductor 
. 1N5819 diode
. 274 k resistor (1% tolerance) 
. 100 k resistor (1% tolerance) 
. 100 µF capacitor 
. USB socket 
. MAX 630 CPA integrated circuit 
It’s the same old story—just when you want to talk 
on your cellphone, the battery goes flat and the 
conversation is irretrievably lost! Invariably, you 
haven’t got your phone charger on you, and even 
if you did have it wouldn’t be an awful lot of help 
as the chances are there is no power for miles 
around . . . 
At the Centre for Alternative Technology, U.K., 
there is a solar-powered phone (see Figure 13-3); 
while this is powered by clean green energy, it 
can’t claim to be very portable! 
In this project, we are going to build a circuit 
that will provide a supply capable of powering 
either a cellphone or PDA charger. A PDA is about 
the limit of what you can charge using small cells, 
a laptop charger is probably a bit ambitious. 
One of the problems with trying to build this 
circuit is that finding a suitable connector for 
many mobile phones is a real problem. While 
Nokia makes life easy by providing a simple jack 
that can be readily obtained from many component 
suppliers, many other manufacturers rely on 
proprietary connectors which are nonstandard 
and awkward to source. 
For this reason, we have based this project on 
hacking a cellphone car charger. 
There are two schematics here for projects that 
tackle the project from slightly different angles. 
The first method involves creating a solar array 
that will provide above 12 V—regulating this 
supply to 12 V, and charging the device via a 
hacked “car charger” (Figure 13-4). The other 
device is suitable for where a USB type charger is 
available—this is ideal for USB mp3 players, 
PDAs and mobile phones, most of which now 
come with a “data” lead. We have an array of 
solar cells, which charges a couple of batteries 
when there is spare power; a voltage regulator then 
turns this into a clean 5 V, which can be used to 
drive the device (Figure 13-5). The advantage of 
this circuit is that even if there is not a lot of sun— 
or it is night-time, you can pop a couple of freshly 
charged batteries in (maybe from your solar 
charger?) and things will start working. 
Car chargers are designed to allow you to plug 
your phone into your vehicle’s cigarette lighter or 
accessory socket. They are cheap and readily 
available; however, they rely on having a car 
present to allow you to charge your phone! 
There are a couple of ways of making this project. 
You can either build the project as a box into 
which you plug your car cellphone charger, 
or, if you are a little more adventurous, you can 
take apart the cellphone charger and integrate it 
121 
Project 33: Build Your Own Solar Phone Charger 
Figure 13-3 A solar-powered phone—albeit not all 
that portable.
properly into the box. The plus side of keeping 
the two pieces separate is that you can use the car 
cellphone charger as a stand-alone item, or, you 
can power it from the “solar box.” The plus side of 
integrating it all together is that it makes for a neat, 
stand-alone project and the two parts cannot become 
separated. 
122 Project 33: Build Your Own Solar Phone Charger 
Figure 13-4 Solar-powered phone charger schematic: car charger. 
Figure 13-5 Solar-powered phone charger schematic: USB type. 
Note 
A note on cigarette lighter sockets—the usual 
wiring scheme is that the casing of one of these 
sockets is connected to the negative terminal of 
the battery
123 
Project 34: Build Your Own Solar-Powered Radio 
Project 34: Build Your Own Solar-Powered Radio 
You will need 
. Ferrite rod antenna 
. 60–160 pF variable capacitor 
. BC183 transistor 
. 10 nF capacitor 
. 0.1 mF capacitor × 2 
. 470 µF capacitor 
. 220 R resistor 
. 1 k resistor 
. 100 k resistor × 2 
. 10 k potentiometer 
. Speaker 
. PV cell 
. PCB stripboard 
Tools 
. Soldering iron 
. Solder 
A solar radio is another great idea! Never mind 
“Desert Island Discs,” with a solar radio, you can 
ensure that if you are ever marooned, you are able 
to listen to your favorite radio stations! 
In this circuit we are going to build a simple AM 
radio that is powered by the sun. 
There are some commercially available radios 
powered by solar energy; however, it is relatively 
easy to build your own. We are basing this circuit 
around the MK484 integrated circuit, which takes 
all the hassle out of building a simple radio. The 
integrated circuit looks like a transistor with three 
pins, and reduces the amount of external components 
needed considerably. 
The schematic for the circuit is shown in 
Figure 13-6. 
The radio has two controls. The variable capacitor 
changes the frequency that you are tuned to, and 
the potentiometer acts as a volume control for the 
simple transistor amplifier. 
There are a number of commercially available 
solar radios; one idea for mounting, which you 
Figure 13-6 Solar AM radio schematic.
could easily accomplish with the solar radio circuit 
above, is to mount the circuit in a set of headphones, 
like the solar radio shown in Figure 13-7. 
The radio in Figure 13-8 is the “Freeplay” 
wind-up radio invented by Trevor Bayliss. It uses 
two renewable energy sources—solar power, and 
for less sunny days “human wind-up power” in 
order to make sure that even when the sun doesn’t 
shine, you aren’t without your tunes! 
124 Project 35: Build Your Own Solar-Powered Torch 
Figure 13-7 Headphone mounted commercial solar Figure 13-8 “Freeplay” wind-up and solar radio. 
radio. 
Project 35: Build Your Own Solar-Powered Torch 
You will need 
. 4× 1.5 V solar cells 
. 1× AA 600 mAh NiCad battery 
. 1N5817 Zener diode 
. 220 k 1/4 W carbon film resistor 
. 100 k 1/4 W carbon film resistor 
. 91 k 1/4 W carbon film resistor 
. 10 k 1/4 W carbon film resistor 
. 560 R 1/4 W carbon film resistor 
. 2× 3.3 R 1/4 W carbon film resistor 
. C9013 NPN transistor 
. C9014 NPN transistor 
. C9015 PNP transistor 
. 300 pF ceramic capacitor 
. 100 nF ceramic capacitor
. 1 nF ceramic capacitor 
. 82 µH inductor 
. CdS photocell 47 k @ 10 lux 
. 2 × LEDs 
In lists of made-up useless things, solar-powered 
torches seem to come out somewhere at the top. 
After all, what use is there for something that 
produces light that is powered by light? Until you 
realize that we can use batteries to store the 
energy—this is a crucial leap in understanding! 
Now doesn’t the solar torch seem so much more 
interesting? 
A solar torch is a useful thing to build and then 
leave on a sunny window sill. In the event of a 
power cut, you know that you can go to your trusty 
solar torch to provide a (somewhat modest) 
amount of illumination! 
Figures 13-9 and 13-10 show a solar-powered 
torch and the solar torch in its packaging. One of 
the things you need to think about if you are going 
to house your project in a round torch case, is that 
you will need to ensure that either: 
. The torch is weighted so that it rolls in such a way 
that the solar cell points upwards. 
or 
. There is a flat machined into the case, which 
ensures that the solar cell points upwards when the 
flat in the case rests on a level surface. 
Tragedy would strike if your solar torch were to 
roll over so that the flat faced away from the 
ground—blocking sunlight to the solar cell! 
The circuit is shown in Figure 13-11. It is a 
variation of the outdoor solar light circuit (which 
you will see later in this chapter), where a pair of 
resistors and a switch are used to mimic the action 
of the photocell. It allows manual control of the 
LEDs and economizes by only using a single 
battery. 
125 
Project 35: Build Your Own Solar-Powered Torch 
Figure 13-9 Solar-powered torch. 
Figure 13-10 Solar-powered torch in its packaging.
126 Project 36: Solar-Powered Warning Light 
Figure 13-11 Solar-powered torch schematic. 
Project 36: Build Your Own Solar-Powered 
Warning Light 
You will need 
. Capacitor 0.1 F, 5.5 V 
. Capacitor 100 µF 
. Capacitor 6.8 µF 
. 2 × resistors 100 k 
. 2 × resistors 100 ohms 
. PNP transistor 
. NPN transistor 
. 2 × diodes 1N4148 
. Super-high brightness red LED 
. 100 µH inductor 
. 4 × small solar cells 
Tools 
. Soldering iron 
There are many applications where it is useful to 
have some sort of warning light, strobe, or beacon. 
Often, the place where you want to position the 
warning light or strobe is totally remote from any 
source of power. Although we can often run things 
from batteries, sometimes we want to put a light 
where changing a battery would be undesirable. 
Solar energy, as well as producing clean renewable 
energy, also allows us to power things in remote 
places that would not easily be accessible using 
conventional cables, or where changing a battery 
could present a problem. 
In Figure 13-12 we see a commercially available 
solar waterproof warning light, there are many 
applications for this—you might want to strap it to 
your back while cycling, for instance. 
The beacon has a couple of modes. When the 
beacon is set to off, the solar cell will charge the 
battery; however, the light will not flash under any 
circumstances. In “solar” mode, the beacon will 
charge during the day, and when the circuit senses 
a low lighting condition, the beacon will begin to 
flash using the power stored in the rechargeable 
battery. Set to “on” the beacon will flash regardless
of whether it is light or dark—however, bear in 
mind that this will drain the battery. 
If you are going to use this beacon outside all of 
the time, you might want to think about how you 
can protect the circuit (Figure 13-13) against the 
ingress of water and solid matter. Most suppliers 
of cases sell a range of decent waterproof cases 
that are eminently suitable for outdoor use, or 
you may find that you can improvise with a 
Tupperware or similar container to produce a 
satisfactory housing. 
127 
Project 37: Build Your Own Solar-Powered Garden Light 
Figure 13-12 Solar waterproof warning light. 
Figure 13-13 Solar waterproof warning light schematic. 
Project 37: Build Your Own Solar-Powered Garden Light 
You will need 
. 4 × 1.5 V solar cells 
. 1 × AA 600 mAh NiCad battery 
. 1N5817 Zener diode 
. 220 k 1/4 W carbon film resistor 
. 100 k 1/4 W carbon film resistor 
. 91 k 1/4 W carbon film resistor 
. 10 k 1/4 W carbon film resistor 
. 560 R 1/4 W carbon film resistor 
. 2 × 3.3 R 1/4 W carbon film resistor 
. C9013 NPN transistor 
. C9014 NPN transistor 
. C9015 PNP transistor 
. 300 pF ceramic capacitor 
. 100 nF ceramic capacitor 
. 1 nF ceramic capacitor 
. 82 µH inductor 
. CdS photocell 47 k @ 10 lux 
. 2 × LEDs
Tools 
. Soldering iron 
Solar-powered path lights (Figure 13-14) are 
becoming ubiquitous in just about every garden 
center nowadays! There are lots of advantages to 
using solar power rather than a hard-wired system. 
First of all, as a hard-wired system is exposed to 
the elements, you need to ensure that you use 
low-voltage fixtures and fittings, which require 
a transformer to step down the voltage, or failing 
that, really expensive mains fixtures and fittings. 
Then the next thing to consider is that even the 
safest low-voltage system is still vulnerable to the 
gardener’s spade—a badly placed spade can mean 
disconnection of your garden lighting system. 
Solar-powered garden lights have none of these 
disadvantages. They charge their batteries during 
the day, and then at night as the light fades, they 
switch on, providing illumination. 
The change in illumination is detected by a CdS 
photocell. 
We will be using LEDs for this project (Figure 
13-15) as they provide good efficiency—a decent 
amount of illumination for the relatively small 
amount of energy we are able to provide. 
128 Project 37: Build Your Own Solar-Powered Garden Light 
Figure 13-14 Solar garden light. 
Figure 13-15 Solar garden light schematic.
Tracking the Sun 
Chapter 14 
One school of thought advocates positioning your 
solar panels on a fixed surface such as a roof, 
positioned so as to harness as much sun as possible 
on average over the year. This approach certainly 
works, but as we saw in Chapter 3, the sun is not a 
fixed object in the sky—it moves, and so this 
approach is not necessarily the best. 
One other solution is to actively track the sun 
using a device such as the trackers shown in 
Figures 14-1 and 14-2. What this entails is using 
motors, hydraulic actuators, or some other devices 
to move our solar panels to follow the sun. This 
approach does have some merits. With the sun 
always facing the panels as face-on as possible, the 
most possible energy is extracted, as the panels are 
operating at their greatest efficiency. 
One of the main caveats of this design is that 
moving the panels does require some input of 
energy, and this must of course be subtracted 
from the total energy that the panels are 
producing. 
Furthermore, in some scenarios this is inappropriate—
if you are roof-mounting panels, it would 
not really be appropriate to “reposition your roof” 
every time the sun moves. 
In this chapter we will build a circuit that can be 
used to track the sun’s movements and move a 
solar panel accordingly. The circuit is only 
simple, and will power a small motor to drive a 
demonstration display; however, with correct 
driver circuitry, the circuit could easily be scaled 
up to move bigger arrays. 
129 
Figure 14-1 Solar tracker at Llanrwst, near Snowdonia, Wales. Image courtesy Dulas Ltd. 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
130 Project 38: Simple Solar Tracker 
Figure 14-2 Solar tracker at Llanrwst, near Snowdonia, Wales. Image courtesy Dulas Ltd. 
Tip 
If you don’t fancy building your own solar tracker 
from scratch, Science Connection sells one as a 
kit under the stock code number 2216KIT. Full 
details are in the Supplier’s Index. 
www.scienceconnection.com/Tech_advanced.htm 
Project 38: Simple Solar Tracker 
You will need 
. 3 × LDR 
. 33 R resistor 
. 75 R resistor 
. 100 R variable resistor 
. 10 k variable resistor 
. 20 k variable resistor 
. 2N4401 transistor 
. TIP120 Darlington pair 
. 9 V relay 
. 5 V motor
How the circuit works 
We have three CdS photoresistors (Figure 14.3) 
The value of these resistors is about 5 k when not 
exposed to light. However, when we expose them 
to light their resistance decreases to around about a 
couple of hundred ohms. 
The third CdS cell is mounted in a shrouded 
enclosure so that it is only illuminated when it 
faces directly toward the sun. When the sun illuminates 
this photocell, its resistance drops, and as a 
result, when the sun shines on it, our Darlington 
pair is kept off. 
When the sun moves away from the line of sight 
of photoresistor 3, its resistance increases. This 
allows our Darlington pair to switch on, which in 
turn drives our relay, which in turn drives our 
motor to move the array. 
The variable resistor in line with the relay and 
motor allows us to regulate the motor’s speed. The 
motor should turn slowly enough to move the 
array, but not so fast that the array overshoots 
before photoresistor 3 has a chance to respond to 
the change. 
Photoresistor 2 is mounted flush with the panel 
so that it can see the whole sky. Its function is to 
check that the sun is present, to prevent the array 
from searching for a sun that isn’t there! If the sun 
is present it will sense this and drive the base of 
our NPN transistor low. However, if the sun 
disappears behind a cloud its resistance rises and 
our NPN transistor base is allowed to be high, this 
in turn drives the base of our Darlington pair low, 
which prevents the tracker from tracking. 
Our first photoresistor is mounted on the back of 
our tracker. It senses the new light coming from 
the east and activates the turntable to allow our 
solar panels to face the sun to catch the new light. 
The setup for our solar array and sensors is 
illustrated in Figure 14-4. 
131 
Project 38: Simple Solar Tracker 
Figure 14-3 Simple solar tracker schematic. 
Hint 
If you want to adjust the sensitivity of a CdS 
photoresistor without fiddling with the 
electronics, you can decrease its sensitivity to 
light by drawing on a section of the sensing 
element with a black permanent marker. This 
prevents some light reaching the sensor. 
Tip 
Poulek Solar, Ltd., whose website is www.solartrackers.
com sell commercially produced solar 
tracking circuits and all of the hardware to mount 
your panels on a sturdy outdoor tracker. See 
Supplier’s Index.
Taking it further 
You don’t have to use this simple circuit just to 
move a solar panel, you can think of ways to move 
any of the solar projects presented in this book. 
You might want to move a solar cooker for example. 
The motor used in the circuit might only be small; 
however, you can use gearing to enable it to move 
larger loads. We only want slow motion from our 
motor anyway, so slow movement is ideal. 
Solar trackers in the 
real world 
Now we have built a model, let’s take a look at a 
real solar tracker and gain some insight as to the 
capabilities of the technology. 
132 Project 38: Simple Solar Tracker 
Figure 14-4 Solar array and sensors setup. 
Online resources 
If you want to explore more sophisticated solartracking 
devices, here are some links to hobbyists 
pages which will take you further in your design 
of solar trackers. 
pages.prodigy.net/rich_demartile/ 
www.redrok.com/electron.htm#tracker 
www.phoenixnavigation.com/ptbc/articles/ 
ptbc55.htm 
Mr Howie, Scotland 
Here, it was decided that solar trackers were the 
way forward, as the roof structure of the house on 
the property was not strong enough to support a 
solar array, and the rafters were irregularly 
spaced—making it difficult to install mounting 
hardware. As the property was surrounded by a 
lot of land, it was decided that it was cogent to 
install a stand-alone array. As Scotland is at quite 
a high latitude, it was decided that using a solar 
tracker would make the best use of the available 
solar resource. 
The array (Figure 14-5) is 1.92 kW peak, and 
was 48% funded by an Energy Saving Trust grant.
133 
Solar Trackers in the Real World 
Figure 14-5 Solar tracker on the property of Mr Howie, Scotland. Image courtesy Dulas Ltd.
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Solar Transport 
Chapter 15 
Why solar transport? 
The way that we live today necessitates traveling 
long distances—whereas historically all travel was 
on foot, we are now assisted by cars, boats, and 
trains to get us from place to place. 
Our world has shrunk—low-cost air travel 
now means that we can be anywhere in the 
world affordably within the day, and the car 
means that we can travel almost anywhere local 
by road in a matter of minutes. 
Our world today has been styled and shaped by 
our transport patterns. Many people live in the 
suburbs and commute for what would have been 
incredibly long distances in the past to get to their 
places of work, shops, and amenities. 
Where in the past shops were a local affair, now 
we go to large sprawling out-of-town shopping 
centers and malls. 
All of this increased transport affords us endless 
convenience, but what is the real cost? 
The environmental cost of 
transportation 
The city of Los Angeles in the U.S.A. is an example 
of a city that has learnt to pay the price for heavy 
use of transportation. The city’s urban planning has 
dictated that people use their own private vehicles, 
as public transportation is poor. 
Transportation uses the bulk of the world’s 
petroleum. We use petrol or gas (depending on 
which side of the pond you come from), because it 
is an energy-dense, readily-available (at present) 
fuel, which provides power-on-demand when we 
want it. 
However, imagine a world without cheap gasoline 
. . . How would we get about? As Chapter 1 
mentioned, a world without petroleum may be here 
sooner than we think. 
Furthermore, the burning of lots of gasoline and 
diesel results in all sorts of “nasties” going into the 
air that you and I breathe—this includes carbon 
dioxide, oxides of sulfur which are responsible for 
acid rain, oxides of nitrogen, particulates, and 
unburnt hydrocarbons. We are putting this lethal 
cocktail into our air day-by-day. 
What are the alternatives? 
Well, for a start we can try to change our transport 
patterns. Social fixes like this are really cheap 
and necessitate minimal investment. What this 
means in practice is drive less and fly less. It 
might sound tough, but in fact it really is easy to 
make a conscious effort to reduce our transport 
patterns. 
Also, in addition to trying to reduce the amount 
that we travel, we can try to reduce the amount 
that other people have to travel. This could be 
done, for example, by sourcing locally produced 
products. 
We can try and reduce our carbon emissions by 
using public transportation—it follows that it is 
more efficient to move a large number of people 
than a small number of people—the efficiency 
gains and economies of scale mean that we save 
fuel and avoid many emissions. 
135 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
136 Solar Transport 
However, there must be alternatives to our present 
fossil fuel-based vehicles, and yes there are. You’ll 
never guess what . . . these alternatives are solar 
derived as well! Read on and see what the exciting 
technology has in store. 
Solar vehicles 
At the moment, solar cars aren’t really practical for 
you and I to drive about in—simply too much 
surface area is required to mount the solar cells. 
Also, some method of storing the solar energy 
needs to be employed for when your car goes into 
a tunnel or the sun hides behind a cloud. Even so, 
solar vehicles such as the Honda Dream shown in 
Figure 15-1 are an interesting demonstration that 
it is possible to produce a vehicle that runs on 
solar energy. 
There are a number of competitions that aim to 
spur on the development of solar vehicles, two 
notable competitions are the World Solar Challenge, 
and the North American Solar Challenge. If 
you are really keen on getting into solar vehicles, 
some of the top universities enter cars into the 
races. 
OK . . . so entering a full-size solar car into a 
race is a little bit pricey (Figure 15-2), but what 
can you do instead to fulfill your solar ambitions? 
Follow the next project and find out how to build a 
simple solar vehicle! 
Figure 15-1 Honda dream car. Image courtesy Honda. 
Online resources 
Take a peek at the World Solar Challenge website 
to see what is going on 
www.wsc.org.au/ 
Also, the North American Solar Challenge is 
here 
www.americansolarchallenge.org/ 
Online resources 
Check this website about solar vehicles for some 
cool information 
www.formulasun.org/education/seles9.html/
137 
Project 39: Build Your Own Solar Car 
Figure 15-2 Solar vehicles lined up for a solar car race. Image courtesy NASA. 
Project 39: Build Your Own Solar Car 
In this project we will be building a small solar 
vehicle that demonstrates how solar power can be 
used to propel a small vehicle. In the next projects, 
you will learn how to “soup up” your racers and 
race them. 
You will need 
. SolarSpeeder 1.1 printed circuit board (PCB) 
. High-efficiency coreless motor 
. Motor mounting clip 
. 3 × Rubber wheels on nylon hubs 
. 43 mm long 1.40 mm diameter (1.7 in. long, 
0.055 in. diameter) steel rod 
. 2 × Black plastic wheel retainers 
. 0.33 F 2.5 V gold capacitor 
. 2n3904 transistor 
. 2n3906 transistor 
. 1381 voltage trigger 
. 2.2 k resistor (color bands red/red/red/gold) 
. SC2433 24 × 33 mm 2.7 V solar cell 
. Pair solar cell wires 
. 25 mm (1 in.) length 18 gauge wire 
Tools 
. Soldering iron 
. Needle-nose pliers 
. Side-cutters or strong scissors 
. File and/or sandpaper 
. Glue, rubber cement, or hot-glue (or superglue, if 
you’re very careful) 
. Safety glasses—very important when clipping and 
snipping!
First, assemble all of the components for the 
Solaroller as in Figure 15-3. 
When our project is complete, it will look like 
the pretty little bug in Figure 15-4. 
First of all, take a look at the schematic in 
Figure 15-5. This is a pretty standard design for a 
solar engine. What is happening here is that our 
138 Project 39: Build Your Own Solar Car 
Note 
A full kit of parts for the following project is 
available from Solarbotics at 
www.solarbotics.com 
Figure 15-4 The assembled Solaroller. Image courtesy Solarbotics. 
Figure 15-3 Components of the Solaroller.
little solar cell is providing electrical energy which 
is charging the high-capacity capacitor. When the 
voltage reaches a certain threshold level, the 1381 
triggers the output circuit, which dumps the power 
in the capacitor through the motor, creating 
movement. 
The first step of assembling your Solaroller is 
illustrated in Figure 15-6. You are going to need to 
take the axle and thread it through the two holes in 
the circuit board named “rod.” 
Next, take the high-capacity capacitor, bend the 
leads so that they are flush with the body of the 
capacitor. Then solder it into the PCB. Ensure that 
you solder this in the correct orientation. 
Next, take the 2.2 k resistor and solder it as shown. 
The orientation of the resistor is unimportant. 
The next stage in assembly is shown in 
Figure 15-7. 
First take the 3904 transistor and solder it at the 
head of the board in the orientation shown in 
Figure 15-7. 
Now the 1381 and 2906 transistors are soldered 
in either side of the board facing down. This is also 
illustrated in Figure 15-7. 
Finally take the small fuse clip which will be 
acting as our motor mount and solder it into the 
bottom of the board. Note that the fuse clip has a 
small lip to prevent the motor sliding out. Ensure 
that you orient this correctly. 
Now you have got this far you are definitely 
cooking with gas! . . . or should that be with solar? 
Now take the small high-efficiency motor and 
insert it into the fuse clip in the manner shown in 
Figure 15-8. 
139 
Project 39: Build Your Own Solar Car 
Figure 15-6 Step 1—assembling the Solaroller. Image 
courtesy Solarbotics. 
Figure 15-5 The Solaroller schematic. Image 
courtesy Solarbotics. 
Figure 15-7 Step 2—assembling the Solaroller. Image 
courtesy Solarbotics.
Adding the wheels at the front is a simple 
procedure of pushing them onto the axle and then 
adding the small black plastic clips which will 
retain the wheels and prevent them from sliding 
off. Now take the motor leads which are very delicate 
so treat them with a lot of respect! The red 
one should be soldered into the hole on the PCB, 
the blue one should be soldered onto one of the 
holes near the fuse clip (Figure 15-9). 
Next take a small piece of thick copper wire 
and separate the insulation from the copper wire 
(making sure that you keep the insulation intact as 
we will be needing this later!). The wire should be 
bent at one end and soldered first into the hole 
adjacent to the motor clip, and then to the motor clip 
itself to provide mechanical support (Figure 15-10). 
140 Project 39: Build Your Own Solar Car 
Figure 15-8 Step 3—assembling the Solaroller. Image 
courtesy Solarbotics. 
Figure 15-10 Step 5—assembling the Solaroller. 
Image courtesy Solarbotics. 
Figure 15-9 Step 4—assembling the Solaroller. Image 
courtesy Solarbotics.
Next, take a short length of that insulation that 
you saved and slide it onto the motor shaft. Now 
take the wheel and slide it over the insulation 
(Figure 15-11). 
The next step is dead simple! Trim the axles at 
the front of your Solaroller (Figure 15-12). 
Now tin the pads on the back of the solarcell 
(Figure 15-13). 
Now solder the wires to the tinned pad, and add 
a little dab of glue in an area away from the soldered 
joints to act as a strain relief (Figure 15-14). 
141 
Project 39: Build Your Own Solar Car 
Figure 15-11 Step 6—assembling the Solaroller. 
Image courtesy Solarbotics. 
Figure 15-12 Step 7—assembling the Solaroller. 
Image courtesy Solarbotics. 
Figure 15-13 Step 8—assembling the Solaroller. 
Image courtesy Solarbotics. 
Figure 15-14 Step 9—assembling the Solaroller. 
Image courtesy Solarbotics.
142 Project 40: Hold Your Own Solar Car Race 
Figure 15-15 Step 10—assembling the Solaroller. 
Image courtesy Solarbotics. 
Project 40: Hold Your Own Solar Car Race 
You will need 
. A stopwatch 
or 
. Lap timer 200 software and a PC 
. A number of solar cars 
OK, so the World Solar Challenge, and the North 
American Solar Challenge might be a little out of 
your reach; however, holding your own tabletop 
solar car race certainly isn’t. 
The free lap timer software presents a high-tech 
alternative to simply using a stop watch to time 
your cars. The software comes with schematics to 
build a PC interface for sensors which will sense 
when your car crosses the line. 
You might like to consider how you can make 
your team vehicles look different. A little customization 
with paint and graphics goes a long 
way! 
Tip 
Lap timer software is a free download from: 
www.gregorybraun.com/LapTimer.html 
Now solder the connections to the printed circuit 
board (Figure 15-15). 
Hold the cell to the light, supporting your solar 
vehicle and check that it works. Now that you have 
proved that the circuitry works, fix the solar cell to 
your vehicle chassis.
143 
Project 42: Supercharge Your Solaroller 
Project 41: Souping Up Your Solar Vehicle 
. Think about how you could make a solar 
concentrator with tin foil or Mylar reflective 
surfaces channeling more energy to your solar cell. 
. Experiment with different tire types. You might find 
that some different wheels from another model car 
offer better grip. 
. Try replacing the front wheels with some kind of 
skid. Think about reducing the Solaroller’s friction; 
however, as you reduce friction, you might also 
reduce control or the model’s ability to travel in a 
straight line! 
. You can tweak the value of the 2.2 k bias resistor. 
This will change the efficiency of the solar engine. 
Higher values will make your solar engine more 
efficient, but will increase the time taken to 
charge. Smaller values will speed the rate at 
which the motor is triggered, but at the expense 
of efficiency. 
Project 42: Supercharge Your Solaroller 
Additionally, you can add a diode which allows 
your Solaroller to charge more than would normally 
be possible. You have the option of using a 
bog standard glass diode or an LED. 
The first thing you will need to do is cut through 
the PCB trace in Figure 15-16. 
The next thing to do is take your diode, and 
solder it as shown in Figure 15-17. Make sure that 
you orient the stripe on the diode or flat on the 
LED correctly. 
Figure 15-17 Adding the diode. Image courtesy 
Solarbotics. 
Figure 15-16 Cutting through the PCB trace. Image 
courtesy Solarbotics.
144 Solar Aviation 
Figure 15-18 Honda fuel cell vehicle. Image courtesy Honda. 
Fuel cell vehicles 
In Chapter 17, you will learn about hydrogen fuel 
cells. Hydrogen isn’t a fuel as such—you can’t 
“dig it out of the ground,” and although it is the 
most common element in the universe, we can’t 
access it in a readily usable way. 
However, we are surrounded by water which is 
H2O, this means that it contains two parts of 
hydrogen for every part of oxygen. 
As you will see in Chapter 17, it is relatively 
easy to separate the hydrogen from the oxygen by 
passing an electric current through the water. 
There are other ways of producing hydrogen, but 
whatever the method, this hydrogen can then be 
used as an energy carrier to provide power for a 
fuel cell vehicle, such as the Honda FCX in 
Figure 15-18. 
Solar aviation 
Figures 15-19 to 15-21 show examples of 
solar-powered flight. Figure 15-22 shows a 
fuel cell.
145 
Solar Aviation 
Figure 15-19 Centurion solar plane. Image courtesy NASA. 
Figure 15-20 Helios solar plane. Image courtesy NASA.
146 Project 43: Build Your Own Solar Airship 
Figure 15-21 Helios 2 solar plane. Image courtesy NASA. 
Figure 15-22 Helios fuel cell diagram. Image courtesy NASA. 
Project 43: Build Your Own Solar Airship 
You will need 
. Solar airship tube (8 m of thin plastic tube) 
. 2 × cable ties 
. Tether line (50 m) 
This project is one of the most ridiculously simple 
projects in this book, yet it is also one of the most 
visual and almost counterintuitive. 
You might be under the misapprehension that to 
get things into the air you need sophisticated jet 
engines or rocket thrusters. Certainly if you have
read my other book 50 Model Rocket Projects for 
the HomeBrewPower (intentional plug) you will know 
all about rocket motors and what they can do—but 
hang about! There are also much simpler ways of 
getting things to fly, and believe it or not, they 
involve solar energy! 
The procedure for flying a solar airship is 
simplicity itself. Take the long plastic tube. Put a 
cable tie around one end. Then, holding the other 
open, run until the tube is full of air. Try and fill it 
as much as you can and then bunch up the end and 
tie it tight with another cable tie. Attach the tether 
line to one of the cable ties. 
Now, place your solar airship in the sun and 
watch what happens. 
Gracefully, slowly, you will see your solar airship 
begin to twitch a little, and then rise into the 
air. Hang on to that tether—else it might escape 
you (Figure 15-23)! 
As the airship ascends into the sky, you might 
like to take a few moments to think about what is 
happening here. 
Look at hot air balloons—they are lifted by burning 
gas, a hydrocarbon, but what actually happens 
is that the gas is heating the volume of air inside 
the balloon. As the air is heated, it becomes less 
147 
Project 43: Build Your Own Solar Airship 
Note 
The kit for this project is well worth the spend, if 
only for the enormous scale of the airship—it is a 
massive 8 meters long. However, if you want to 
experiment, you could get some good results with 
cheap black plastic bin liners—why do I say 
cheap? Well cheap bin liners tend to be made out 
of thinner plastic and so are lighter for the 
amount of air they enclose. As they are already 
sealed at one end, you can get away with one 
cable tie for one end, and some fine fishing line 
for the tether. 
Online resources 
Solar airship links 
Here are a number of places on the web where 
you can buy your own solar airship tube. 
www.eurocosm.com/Application/Products/ 
Toys-that-fly/solar-airship-GB.asp 
www.amazon.co.uk/exec/obidos/ASIN/ 
B000279OKI/202-9916112-9335805 
www.find-me-a-gift.co.uk/gifts-for-men/ 
unusual-gadgets/solar-airship.html 
www.comparestoreprices.co.uk/novelty-gifts/ 
unbranded-8m-solar-air-ship.asp 
This experiment has got to be seen to be 
believed! If you want to check out someone else 
doing it first, you might like to take a look at this 
video on the net. 
www.watchondemand.co.uk/solar-airship.htm 
Figure 15-23 Solar airship.
dense and therefore wants to float above denser 
air—this provides a lifting force. Simple really! 
What does the future 
hold? 
Space travel has long been a dream of futurists and 
science fiction lovers alike. However, traversing the 
voids of space presents a number of problems—one 
of which is where does the energy come from to 
propel a vehicle all that distance through space? 
One possible answer could come in the form of 
a solar sail (Figure 15-24). 
The sail shown in Figure 15-25 would be estimated 
to be half a kilometer across! Although the 
push provided by solar radiation is small, being 
harnessed over such a large area it is strong 
enough to provide propulsion. 
148 What Does the Future Hold? 
Figure 15-24 Could solar sails be used for space 
travel? Image courtesy NASA. 
Figure 15-25 A solar sail unfurled in flight. Image 
courtesy NASA.
Solar Robotics? 
Chapter 16 
I would like to thank Dave Hrynkiw at Solarbotics 
Ltd for his help in preparing this chapter. 
Over the past century, we have seen a relentless 
march toward a world of automation and ease. 
Ever since the industrial revolution, increases 
in efficiency have been made by using automatic 
devices and robots to take over the menial tasks 
of man. 
As a result, we have given ourselves over to the 
machine, and our modern world is dependent upon 
the functioning of these devices for our continued 
development and growth. 
This presents us with a little bit of a dilemma. 
The machines and automation of the industrial 
revolution were fueled by coal. More recently, oil, 
natural gas, and other fossil fuels have powered the 
wheels of industry and automation. While automation 
requires less human input, it does require 
energy. 
Thus we have enslaved ourselves to previously 
plentiful fossil fuel energy, and created a world 
which would be much changed without it. 
In the field of energy and robotics, we could then 
go on to say that if we want to push the boundaries 
of what we know, into the deep uncharted realms 
of space, exploring other planets (Figure 16-1) 
(or closer to home, remote inaccessible areas like 
the sea), we need to provide energy for these distant 
ventures—this is hard with conventional 
means. 
149 
Figure 16-1 Spirit Mars rover. Image courtesy NASA. 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
The Spirit Rover which was sent to Mars, was 
equipped with a 140 W array. 
We see the increasing penetration of robots into 
our households—Roomba and Scooba are 
household names and represent readily available 
domestic robots. However, at present, service 
robots need clumsy recharging stations. What if 
your domestic robots could roam freely around 
your house powered by nothing more than the sun 
shining through your window, and the ambient 
light in your rooms? 
BEAM robotics 
BEAM (Biology, Electronics, Aesthetics, and 
Mechanics) robotics differ from traditional robotics 
in one important respect—whereas conventional 
robotics tends to employ a central processor and 
some software to dictate the behavior of the robot, 
BEAM robotics has a different approach. The 
robotic behavior is governed by simple circuits 
which interact with each other in defined patterns. 
The Photopopper Photovore 
The Photopopper Photovore is a nippy little robot 
powered only by solar energy. While very simple 
in nature, it demonstrates that solar-powered 
devices can perform simple autonomous 
functions—this sets a precedent for much larger, 
more complex devices. 
Photopopper behaviors 
Although simple, we see a number of emergent 
behaviors as a result of the simple interconnections 
of the above circuit. 
The first behavior that we see, is a light-seeking 
behavior. This means that our Photopopper will try 
to seek light and avoid shadow wherever possible. 
This behavior was exhibited in Grey Walter’s turtle, 
an early robot which proved that a limited number 
of connections could give rise to more complex 
emerging behaviors. 
We can see the way the robot makes its way 
toward a light source in Figure 16-3. 
When we try and relate our mechanical robot 
beastie to the world of the animal kingdom, we can 
see that light is the “food” for our robot—a natural 
animal instinct is to go where there is food in order 
to survive—it is clear that this robot exhibits this 
behavior trait. 
Another behavior that our robot exhibits is 
“obstacle avoidance” behavior, where the robot 
tries as far as possible to avoid obstacles by using 
its “whisker” touch sensors (Figure 16-4). Again, 
we can relate this to the animal kingdom, where 
whiskered animals such as hamsters and cats sense 
obstructions with their sensitive whiskers and take 
evasive action to avoid those obstacles. 
The circuit that the Photopopper Photovore uses 
is called a “Miller Engine” circuit (Figure 16-2), 
the solar cell charges a power capacitor, which 
stores the power ready to be used in bursts by the 
motor. The circuit uses a 1381 voltage trigger to 
trip the motor circuit, once the solar cell has 
charged the capacitor sufficiently. Once the 
capacitor has discharged beyond a certain point, 
the 1381 cuts off, and stops the motor—allowing 
the capacitor to charge. While you can use this 
circuit as a basis for your own designs, a full kit 
of parts for this robot is available from 
Solarbotics (see the Supplier’s Index). 
Note 
The great news is that all of the above is available 
in a kit from Solarbotics. 
Check out www.solarbotics.com/ for more 
details. 
There is a coupon at the back of this book 
which will help you secure a discount on 
Solarbotics products. 
150 Solar Robotics
151 
Solar Robotics 
Figure 16-2 Photopopper Photovore schematic. Image courtesy Solarbotics.
You might say this is a very nice novelty, but 
where is the practical application? Sensing light 
and touch is an analog for sensing any number of 
variables. Imagine a robotic Hoover that would 
vacuum the carpet of your room, but not when it 
touched a wall or a piece of furniture, powered 
only by the sun and ambient light. Or imagine a 
robotic lawnmower which would mow the lawn, 
but not where it sensed that there were borders full 
of flowers or garden ornaments. As you can see, 
these behaviors, which on the face of it are very 
simple, can be combined to make an automated 
device that has more complex behaviors, and can 
relieve the tedium of simple human tasks, while 
at the same time not consuming precious fossilfuel 
energy. 
152 Solar Robotics 
Figure 16-3 Photopopper light-seeking behavior. Image courtesy Solarbotics. 
Figure 16-4 Photopopper obstacle-avoiding behavior. Image courtesy Solarbotics.
Now, collect all of the components together for 
your Photopopper. They should look something 
like Figure 16-5. 
Once you have gathered all of your components, 
you need to take your printed circuit board (PCB), 
and the pair of 2N3906 transistors, and solder them 
to the board so that the curved side of the transistor 
matches the curved symbol on the circuit board. 
You can see that the transistors go either side of 
the area marked “Trim Pot.” 
This is illustrated in Figure 16-6. 
Now we move on to Figure 16-7, where we will 
solder the trimmer potentiometer in between the 
two transistors that we have just added to the PCB. 
In this circuit, our trimmer potentiometer acts as a 
“steering wheel” for our robot—we need to calibrate 
it so that our robot travels in a straight line, 
which allows us to manually calibrate our robot. 
The leads will only allow the component to go in 
one way, so it is hard to get wrong. 
We are now going to install the two diodes. Be 
careful when handling these components, as they 
are made of glass, and so are fairly fragile. You 
need to observe the stripe printed on the glass 
casing—diodes will only work correctly if they are 
inserted the right way round, so make sure that you 
get this right. 
If you have bought the Solarbotics PCB, you will 
see that the stripe on the board denotes which way 
to solder this particular component (Figure 16-8). 
Next take the pair of 1381 voltage triggers, and 
solder these in at the top of the board. They need 
to be installed in a similar manner to the transistors, 
with the curve matching the legend on the 
PCB. Take note of the orientation of the components 
in the picture to ensure that the flat sides are 
correctly oriented (Figure 16-9). 
There are now two capacitors which need to be 
soldered at the very top of the circuit board. These 
capacitors are not electrolytic capacitors, so it
153 
Project 44: Assembling Your Photopopper Photovore 
Project 44: Assembling Your Photopopper Photovore 
Figure 16-5 All of the components for the Photopopper Photovore.
154 Project 44: Assembling Your Photopopper Photovore 
Figure 16-6 The transistors—the first stage of 
assembling your Photopopper Photovore. Image 
courtesy Solarbotics. 
Figure 16-7 Adding the trimmer potentiometer. 
Image courtesy Solarbotics. 
Figure 16-8 Installation of the diodes. Image courtesy Solarbotics. 
doesn’t matter which way round they are soldered 
into the two holes. If you are having trouble locating 
the capacitors, take a look at Figure 16-10. 
Now take the two optical sensors, and solder 
them so that the sensing element (which is the 
curved face) is facing outwards as shown in 
Figure 16-11. The optical sensors are photodiodes, 
which allow a variable amount of power to flow to 
the capacitor depending on how much light is 
hitting them. 
Now we are going to install the 4,700 µF power 
capacitor (Figure 16-12). Unlike the two smaller 
capacitors that we installed earlier, this one is 
polarity sensitive as it is an electrolytic capacitor, 
so we need to make sure that we install it the 
correct way round. The capacitor will have a stripe 
in light blue, with minus symbols running down 
next to one lead. The PCB also has a pad marked 
with a minus symbol—so these two need to go 
together. You also need to make sure that the
capacitor lies flat against the circuit board; so you 
will need to bend the leads at 90°, once you have 
ascertained which way round the capacitor is going. 
The next step is to attach the motor mounts for 
the tiny motors which will provide the movement 
for our robot. This is shown in Figure 16-13. These 
motor holders are in fact fuse clips. You need to 
solder them to the two small tabs which stick out 
of the side of the flexible circuit board. There 
is a slight complication here, in that rather than 
soldering the other side of the circuit board where 
the pin protrudes, you need to solder on the same 
155 
Project 44: Assembling Your Photopopper Photovore 
Figure 16-9 Installing the 1381 voltage regulators. 
Image courtesy Solarbotics. 
Figure 16-10 Inserting the two capacitors. Image 
courtesy Solarbotics. 
Figure 16-11 Installing the photodiodes. Image 
courtesy Solarbotics. 
Figure 16-12 Installing the power capacitor. Image 
courtesy Solarbotics.
side as the clip (Figure 16-14). This can be a little 
tricky. 
Some fuse clips come with a little lip molded 
into the metal spring in order to try and retain the 
fuse. If the fuse clip you buy is of this type, you 
need to be able to solder the clip onto the board 
with this side facing the center line of the printed 
circuit board. If you don’t do this, then it will be 
next to impossible to seat the motor comfortably as 
the little lip will prevent the motor from locating 
properly. 
Now, you will notice that the printed circuit 
board is a little bent—this is how it is supposed to 
be; however, in order to keep it rigidly bent, a 
piece of supporting wire needs to be soldered to 
support and maintain tension. You want to take the 
stiff piece of wire, strip some insulation off one 
end, and solder in the place where there is a hole 
marked “wire” near the motor clip. Now, pull the 
piece of wire to the other motor clip, strip the 
insulation from that end, and solder it in place to 
the other hole. 
Once the motor clips are in place (and you have 
given them a while to cool down!) you need to 
think about the small motors (Figure 16-15). If you 
have bought the motors from Solarbotics, they will 
come supplied with a red wire and a blue wire. It is 
important that the correct polarity is observed when 
soldering the motors, as failure to do so will result 
in incorrect operation of your Photopopper. 
The PCB from Solarbotics clearly labels the 
attachment point on the circuit board M-Blue and 
M-Red. Take care when soldering the motor leads, 
as they are delicate and the motor insulation is 
easily damaged by the soldering iron. 
156 Project 44: Assembling Your Photopopper Photovore 
Figure 16-13 Soldering the motor clips onto the PCB. 
Image courtesy Solarbotics. 
Figure 16-14 Both motor mounts ready. Image 
courtesy Solarbotics. 
Figure 16-15 Putting the motors in place. 
Image courtesy Solarbotics.
Also, if you need to strip any insulation from the 
wires, do so very carefully as it is very easy to break 
the connection between the motor and wire—and a 
lot harder to fix it back again! 
Next comes connection of the robot’s 
powerplant— the solar cell. First of all, take your 
soldering iron and tin the pads of the solar cell. 
Then solder a short length of wire to the pads. At 
this point, in order to provide a little strain relief 
for the wires and the carefully soldered joints, you 
might want to take a little hot melt glue or epoxy, 
and glue the wires to an area of the solar cell (for 
example the area between the solder pads) where 
there is no solder. 
You will notice that one of the pads of the solar 
cell is round, and the other is square. The round 
pad is positive and the square pad is negative. So 
solder the black to the square and the red to the 
round. This is shown in Figure 16-16. 
Then, take the wires and, ensuring polarity, 
solder them to the PCB (Figure 16-17). 
The same convention as used on the solar cell 
has been used with the pads on the PCB—the 
round one is a positive terminal and the square one 
a negative. 
This should be a real Frankenstein’s monster 
moment, as your robot will now start to twitch 
with the first indications of light! The circuit is 
now complete, and as the capacitor charges the 
motors will start to whirr! 
Now what you need to do is stick the solar 
cell to the PCB using a double-sided sticky pad 
(Figure 16-18). 
Now take a short 10 mm length of heatshrink 
tubing and slip it over the tiny shaft of one of the 
motors. Using a source of heat, such as a lighter or 
match, shrink the tubing onto the shaft. 
Now comes the fiddly fine-tuning—there is a 
small trimmer potentiometer (trim pot) that you 
157 
Project 44: Assembling Your Photopopper Photovore 
Figure 16-17 Connecting the solar cell to the PCB. 
Image courtesy Solarbotics. 
Figure 16-18 Attaching the solar cell. 
Image courtesy Solarbotics. 
Figure 16-16 Connecting the solar cell. 
Image courtesy Solarbotics.
installed in the center. Well think of this as a bit of 
a manual steering wheel for our Photopopper. 
What this trim pot essentially does is adjust the 
amount that our robot veers to the left or to the 
right. So we can use it to compensate for any stray 
variables that could cause our robot to track off 
center. 
Take a small jeweller’s screwdriver to adjust the 
trim pot. Turn the screw at least 20 times to the 
left—you should find that only the left motor activates. 
Now take the screwdriver and turn it the other 
way. You will find that the other motor activates. 
Now turn the trimmer 10 turns to center it—both 
motors should turn equal amounts at this point. 
If your robot persistently wanders to one side or 
the other, then turn the screw in the direction of the 
engine which needs more power. 
Now we are going to assemble the touch sensors 
for our robot. Take the small Augat sockets, and a 
7 mm length of heatshrink tubing, and shrink the 
tubing onto the socket. 
Now trim the tubing with a sharp knife below 
the neck of the socket and slide off the excess. 
Taking the spring, stretch it a little, and push the 
Augat connector into the center of the spring. 
Follow Figure 16-19 which illustrates the stages of 
constructing the spring/socket assembly. 
Once you have completed this stage, you will 
want to think about soldering it to the circuit board. 
You need to solder the pin to face forward as 
shown in Figure 16-20, and then the spring wire to 
the adjacent pad. 
Now you can curl the wires in different configurations. 
Experiment with making the wires different 
158 Project 44: Assembling Your Photopopper Photovore 
Figure 16-19 Assembling the spring/socket assembly. Image courtesy Solarbotics.
shapes and seeing how it affects their ability to 
sense. Moving the wires to different positions will 
allow the robot to sense different zones in front of 
it. Experiment to see which arrangement makes the 
robot navigate most effectively. 
Building your own 
solar robots 
Armed with these simple principles you can go on 
to create your own solar robots. 
The key to the design is the solar motor schematic 
and interconnection of lots of small simple 
“neuron” circuits. 
Try and buy high-efficiency motors (Figure 16-21), 
as they will produce the best performance from 
relatively modest solar cells. 
You might find old scrap electrical devices to be 
a great source of small motors! Look around for 
Taking it further 
If you want to find out more about BEAM robotics, 
I can highly recommend the publication Junkbots, 
Bugbots & Bots on Wheels by Dave Hrynkiw and 
Mark Tilden, published by HomeBrewPower. 
159 
Project 44: Assembling Your Photopopper Photovore 
Figure 16-20 Attaching the touch sensor to the PCB. Image courtesy Solarbotics. 
Figure 16-21 Solar motors are high-efficiency.
battery-powered, or low-voltage home devices 
which contain motors sufficiently small to be 
driven by solar power. Devices containing tape 
decks yield a variety of small motors (Figure 16-22), 
so look out for old Walkmans, Dictaphones, and 
answering machines especially. 
160 Building Your Own Solar Robots 
Figure 16-22 Electrical devices are a great 
source of motors!
Solar Hydrogen Partnership 
Chapter 17 
“Fuel cell technology is so appealing that it will 
have an enormous impact across all energy 
markets.” K. Atakan Ozbek, Allied Business 
Intelligence Senior Analyst. 
One of the problems that we have seen with 
renewable energy is “intermittency.” Unlike coal, 
gas, and oil, where the amount of energy we 
produce is determined by the amount of fossil fuel 
we input into the process, things with renewable 
energy are slightly different—we must live with 
the energy that the weather gives us. 
This presents us with a choice. We can tailor 
our energy demands to when the energy is 
available. In some situations this is practical; 
however, in most situations, there is an urgency 
to our demand for energy. 
We can meet this demand in a number of ways. 
We can connect together renewable energy sources 
that are distributed over a wide area, “a National 
Grid” as it were. While this is helpful, it is not a 
complete solution—we hope that there will be sun 
in one area when there is not in another, but we 
cannot guarantee it! Furthermore, by transmitting 
electricity over long distances, there is a certain 
amount of “loss” inherent in the system. The electricity 
gets “lost” as a result of resistance, decreasing 
the total amount of useful energy available. 
So, what do we do? Storing the energy would 
seem like an obvious candidate. But the problem is 
that present battery technology is fairly heavy, 
inefficient, and expensive. 
In steps . . . the Fuel Cell. 
The fuel cell—and the hydrogen economy it 
entails—is put forward by many as the answer to 
our impending energy crisis. 
The hydrogen economy entails a transition from 
carbon-rich fuels (such as the fossil fuels we use 
today) to hydrogen, and carriers of hydrogen such 
as methanol. 
Electricity is generated in the usual way from 
renewables—a nice mixed portfolio of wind, solar, 
wave, and tidal energy, producing power as and 
when the weather permits. 
So what is so great about 
the hydrogen economy? 
The hydrogen economy could have a number of 
benefits, both economic and environmental. For a 
start, when you burn hydrogen, you don’t produce 
carbon dioxide, which is produced with carbonbased 
fuels and is a major contributor to the greenhouse 
effect. In addition to this, you don’t get any of 
the other nasties such as oxides of sulfur and nitrogen 
that you get with burning conventional fuels. 
Then there are the economic benefits. At the 
moment, the United States, and many other countries, 
cannot produce enough oil to meet their 
demand for energy. This places those countries in a 
situation where they are dependent upon the 
Middle East and other oil-rich nations to provide 
the energy to power their economies. This is not a 
good position for a country to be in. 
It has bad consequences, as it means that in 
order to get oil, a desperate country might resort to 
any means within its power to secure that vital 
supply of fossil fuel. This could even include war. 
By contrast, there is nothing about hydrogen that 
says it must be produced in a particular location. 
161 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
As long as the two fundamental factors are present—
electricity and water—it can be produced 
anywhere. 
One of the great advantages of the “hydrogen 
economy” is that it works very well with decentralization. 
To understand what decentralization and 
decentralized power generation means, think “don’t 
put all your eggs in one basket.” To explain this a 
little further, at present, power is generated in bulk 
in large centrally managed power stations. This has 
been so because up until now (we have been kidding 
ourselves) there has been an abundance of 
energy-dense fuels that we can use to meet our 
power needs. 
Now envisage a world where rather than polluted 
atmospheres and mountains of toxic nuclear 
waste, we instead have “distributed” energy production. 
This means solar cells on roofs, and wind 
turbines here and there, integrating with the fabric 
of our towns and cities. All of these devices produce 
a small amount of power—but the key is they 
produce it where it is needed. 
How will fuel cells 
penetrate our lives 
in the future? 
You can expect to see fuel cells in all the places 
you see rechargeable batteries at the moment— 
and many more. Fuel cells offer the prospect of 
laptop computers that can be used many times 
longer than conventional batteries allow, mobile 
phones with much longer periods of talk time 
than is possible with present battery technology, 
and vehicles with clean emissions of nothing but 
water. 
“I believe fuel cell vehicles will finally end the 
hundred-year reign of the internal combustion 
engine as the dominant source of power for personal 
transportation. It’s going to be a winning situation 
all the way around—consumers will get an 
efficient power source, communities will get zero 
emissions, and automakers will get another major 
business opportunity—a growth opportunity.” 
William C. Ford, Jr, Ford Chairman, International 
Auto Show, January 2000. 
“Fuel cell vehicles will probably overtake 
gasoline-powered cars in the next 20 to 30 years.” 
Takeo Fukui, Managing Director, Research and 
Development, Honda Motor Co., Bloomberg News, 
June 5, 1999. 
So is there only one type 
of fuel cell? 
No, there are lots! Each type of fuel cell is suited 
to different applications. Broadly speaking, fuel 
cells can be divided into two main kinds—high 
temperature and low temperature. 
Figure 17-1 shows the main areas of focus in 
fuel cell technology, where research capital is 
being invested. 
We are going to be experimenting with a type of 
low-temperature fuel cell—the PEM fuel cell 
which stands for Polymer Electrolyte Membrane, 
or Proton Exchange Membrane depending on who 
you listen to! 
What is a fuel cell made 
up of? 
If we were to take a fuel cell to bits, we would see 
that it is mechanically very simple. Take a peek at 
Figure 17-2. 
We can see that the fuel cell has two end plates. 
These are used as a casing for the fuel cell. They 
help contain the internal elements; furthermore, 
they provide an interface to the connection for 
hydrogen and oxygen gas. 
Next up are the electrodes. These are the pieces 
that allow us to “tap off” electricity. They are 
162 Solar Hydrogen Partnership
generally made from stainless steel, as it does not 
react with the chemicals present. The stainless 
steel is perforated to allow the gas to penetrate. 
The next assembly of carbon cloth/paper and 
Nafion membrane is termed an MEA, or membrane 
electrode assembly. This is the bit that makes the 
reaction take place that produces the energy. 
Next we have a carbon cloth or paper. The gas 
can permeate this quite easily, one side—the side 
that interfaces with the Nafion membrane (more on 
that later)—contains a quantity of platinum which 
acts as a catalyst for the reaction that will take 
place next. 
Now the Nafion membrane—but first a little 
explanation! 
For those of you who were wondering, Nafion is 
a sulfonated tetrafluoroethylene copolymer. Are 
you any the wiser? Well Nafion is a special kind of 
163 
Solar Hydrogen Partnership 
Figure 17-1 Fuel cell technology focus. 
Figure 17-2 Fuel cell construction.
plastic developed by DuPont in the 1960s. It’s very 
special properties are essential to the operation 
of the PEM fuel cell. Essentially, what happens is 
that electrons cannot pass through the Nafion membrane 
but protons can. The platinum on the carbon 
cloth facilitates the separation of the electrons from 
the protons in the hydrogen atom. The protons are 
allowed to pass through the membrane; however, 
the electrons can’t get through. Instead, they take 
the next easiest route. 
The carbon cloth acts as a conductor. It allows 
the electrons to find a path to the stainless steel 
mesh. The mesh forms the electrode, which is 
connected to the circuit that the fuel cell powers. 
The circuit presents the route of least resistance, 
so the electrons make their way through the circuit. 
As they do this they perform some useful work 
which we can harness. 
On the other side of the Nafion membrane is a 
mirror image assembly, with another set of carbon 
cloth, stainless steel electrode, and end plate. 
At the other side, the electrons are reunited with 
the protons that have passed through the membrane, 
and the all-essential oxygen. The protons, 
electrons, and oxygen combine to form H2O— 
better known as water. 
We will look at this process in more detail 
later, but first let’s get on with generating some 
hydrogen! 
164 Project 45: Generating Hydrogen Using Solar Energy 
Project 45: Generating Hydrogen Using Solar Energy 
You will need 
. PEM reversible fuel cell (Fuel Cell Store part no. 
632000) 
. Photovoltaic solar cell (Fuel Cell Store part no. 
621500) 
. Gas storage tank (2 ×) (Fuel Cell Store part no. 560207) 
. Rubber tubing 
. Distilled water (not just purified!) 
Tools 
. Crocodile clip leads 
. Syringe 
In this project, we are going to look at the potential 
for a solar-hydrogen economy. 
We are going to start with a simple experiment 
to generate hydrogen using a solar cell to provide 
the electricity to electrolyze water. 
Familiarizing ourselves 
with the stuff! 
If you have bought the items above, the chances 
are that you have got a lot of cool stuff, but are 
none too sure what to do with it. Don’t panic! 
We are going to look at what the stuff does, and 
how it all goes together in this section. 
First is our fuel cell, shown in Figures 17-3 
to 17-5. 
First of all, you should note two terminals on the 
top—one red, one black. It should be apparent that 
these are the supply terminals for the fuel cell. 
Then, if we look on either side of the fuel cell, we 
see that there are intake pipes for gas. There 
should be two, these are diagonally offset in the 
fuel cell specified above. 
Fuel cell tech spec 
PEM reversible fuel cell 
2 × 2 × 1/2 in. (5 × 5 × 12.5 cm) 
2.4 oz. (68 grams) 
0.95 volts open circuit 
350 MA
You will see that one side of the fuel cell has a 
label “H2,” this is the hydrogen side; the other side 
has the label “O2,” this is where the oxygen goes. 
The fuel cell comes supplied with some little 
caps as shown in Figure 17-3. These can be used 
to prevent water from escaping. These caps can be 
removed if desired, and two little plastic tubes 
are exposed for connection to the gas tanks 
(more about this later). Small lengths of rubber 
tube are shown attached to the fuel cell in Figure 
17-5. 
Next we have the “gas tanks” shown in Figures 
17-6 and 17-7. 
We can see how in the first instance we fill the 
gas tanks with water—this is illustrated in Figure 
17-6. Then, as shown in Figure 17-7, as our fuel 
cells produce gas, the gas displaces the water 
165 
Project 45: Generating Hydrogen Using Solar Energy 
Figure 17-3 PEM fuel cell with caps. 
Figure 17-4 PEM fuel cell without caps. 
Figure 17-5 PEM fuel cell with rubber hoses. 
Figure 17-6 40 ml “gas tank” filled with water.
which goes into the top half of the cylinder. 
The weight of this body of water acting on the 
gas provides a little pressure on the gas—enough 
to speed its return to the fuel cell. 
We also connect the other pipe to the tank to 
enable the excess water to return. 
The fuel cell is connected mechanically as in 
Figure 17-8. Note that the oxygen feed is 
connected in the same manner as the hydrogen. 
Preparing the fuel 
cell for electrolysis 
Before we can electrolyze water, we need to prime 
the fuel cell with water so that it has something to 
electrolyze. For this, we will be using distilled 
water. It is important that the water that you use is 
“distilled water,” which should be readily available 
from the drug store, not just “purified” water. 
Water from the tap, even water from the chiller, 
contains trace elements that have the potential to 
wreak havoc with the delicate little MEA inside 
our PEM fuel cell. 
First of all, you need to prime the fuel cell with 
water. A syringe and some small bore rubber 
tubing helps you accomplish this easily. Fill the 
fuel cell through one of the holes, allowing air to 
escape from the other. Once you have done this, 
put the caps back on the gas intake tubes of the 
fuel cell to prevent any ingress of air. 
Fill the gas cylinders with water as well, and then 
connect it all up as shown in Figure 17-8. If there 
are any little gas bubbles trapped in the pipes, these 
must be bled out of the system first of all. 
Now we come to connecting our solar cell. 
Wiring up the solar cell 
and fuel cell 
Once the “mechanical engineering” is complete, 
we need to work on the “electrical engineering.” 
Luckily, connection is very simple indeed. Take a 
peek at Figure 17-9 which shows how it is done. 
166 Project 45: Generating Hydrogen Using Solar Energy 
Figure 17-7 40 ml “gas tank” filled with gas. 
Figure 17-8 How to connect the pipes to the fuel cell. Figure 17-9 Connecting the two cells.
Logic should tell you that the red terminal on 
the fuel cell is positive and the black terminal is 
negative. Use your crocodile leads to connect things 
up and put your solar cell somewhere where it will 
receive good light. 
Observation 
Don’t hold your breath, the process is going to 
take a little bit of time! Over time you should 
observe a number of things happening. Gas will 
begin to form, and is collected in the two 
cylinders, displacing the water as it does so. You 
will notice that twice as much hydrogen is 
produced as is oxygen. 
What is happening here? 
The chemical symbol for water is H2O. Those 
with even a smattering of knowledge of chemistry 
will know that this means a water molecule is 
comprised of two hydrogen atoms and one 
oxygen atom. 
When we pass an electrical current through the 
water, using the reversible fuel cell as our 
electrolyzer, we are splitting the water into its 
constituent parts—hydrogen and oxygen. 
Because of the membrane inside the fuel cell, 
the hydrogen and oxygen are kept separated. The 
hydrogen and oxygen can then be piped off, and 
stored in tanks, where the hydrogen and oxygen 
can be saved for later use. 
Other methods of 
generating hydrogen 
There are also a number of other proposed 
methods for generating hydrogen from solar 
energy, which, although we are not going to 
examine them in detail here, are certainly of 
merit. 
In fact, at the moment, most hydrogen is produced 
using a process known as steam reforming. 
This takes fossil fuels and combines them with 
steam, which disassociates the hydrogen from the 
carbon, However, do not be fooled! This process 
still leaves a whole lot of carbon dioxide to be 
gotten rid of. 
At the moment, there is talk of a technology 
called “sequestration.” Sequestration involves separating 
the carbon dioxide emissions from industry 
or an item of plant. They are then piped to a facility 
where they can be forced underground into 
natural geological features which supposedly 
will keep the carbon locked up under the earth’s 
surface. Put simply, this technique involves hiding 
the problem by burying it underground. It is a 
good technology in so far as it allows the oil companies 
to maintain the status quo by continually 
producing oil. However, the carbon dioxide is still 
present—albeit “sequestered” underground. There 
is also another incentive for companies to adopt 
sequestration—it increases their oil production! 
By forcing gas underground, more oil comes to 
the surface. Economically it makes good sense, 
environmentally the case is yet to be proven. No 
one has yet tried sequestration on the scale proposed 
before—it is unknown whether this gas will find 
ways of escaping back to the atmosphere. 
One method proposed for making hydrogen 
using solar energy, is to use bacteria to produce it. 
Using a process of photosynthesis, certain algae 
and bacteria have been shown to produce hydrogen 
gas. This hydrogen can be harnessed and used to 
power the hydrogen economy. 
Online resources 
This is a good website to check out that talks 
about the bioproduction of hydrogen. 
www.energycooperation.org/bioproductionH2.htm 
167 
Project 45: Generating Hydrogen Using Solar Energy
You will need 
. PEM reversible fuel cell (Fuel Cell Store 
part no. 632000) 
. Photovoltaic solar cell (Fuel Cell Store 
part no. 621500) 
. Gas storage tank (2×) (Fuel Cell Store 
part no. 560207) 
. Rubber tubing 
. Distilled water (not just purified!) 
. Small load (only a volt or two)/variable resistor 
Tools 
. Ammeter 
. Voltmeter 
We have seen in the previous experiment, how 
we can use electricity, more specifically “solar 
power,” to generate hydrogen. We also saw that 
this hydrogen can be stored for later use. Now, in 
this part of the experiment, we are going to look at 
turning this hydrogen into electricity, and what is 
actually happening. 
In the hydrogen economy, hydrogen which is 
generated from surplus, cheap renewable energy, 
can be distributed through a network of pipes and 
used to provide power in the home via a small 
residential generator (which produces useful heat 
as a byproduct). Additionally, this hydrogen can 
be used to run motor cars or public transportation 
systems if stored in tanks on the vehicle. 
We are now going to see how a fuel cell converts 
this hydrogen back into electrical power. 
Figure 17-10 gives a schematic representation of 
our fuel cell, showing the major parts. 
If we look at Figure 17-11 we can see hydrogen 
entering the fuel cell—ready to do its thing! 
A reaction occurs as a result of the platinum 
catalyst. The electrons cannot go anywhere, as they 
cannot penetrate the membrane formed by the 
MEA, so they go round a circuit because this is the 
easiest path for them to take. Meanwhile, the 
protons escape across the membrane. This is 
illustrated in Figure 17-12. 
As the electrons travel around the circuit, 
they do some useful work. For example, in 
Figure 17-13 they are lighting a bulb. 
168 Project 46: Stored Hydrogen to Create Electricity 
Project 46: Using Stored Hydrogen to Create Electricity 
Figure 17-10 Schematic representation of a PEM 
fuel cell. 
Figure 17-11 Hydrogen enters the fuel cell.
At the other side of the membrane, the electrons 
(which have passed around the circuit), the protons 
(which have crossed through the membrane), and 
oxygen (from either the air or oxygen tanks), are 
brought together, where they react. You can see 
this in Figure 17-14. 
The product of this reaction is water, H2O 
(Figure 17-15). 
This process is happening continuously rather 
than in discrete stages. All the time there is a never 
ending ceaseless flow of electrons, protons, 
hydrogen, and oxygen. 
Connecting up your fuel cell 
We now need to connect up our fuel cell as shown 
in Figure 17-16. The mechanical setup remains the 
same as for the last project. However, rather than 
being connected to a solar cell, we are connecting 
our fuel cell to a load, so that energy can be 
extracted. 
We are monitoring this load with a voltmeter and 
ammeter. 
Instantly, you should see the amount of hydrogen 
and oxygen in the tanks decrease little bit by 
little bit and bubbles flow through the pipes. Your 
load, if it is a small bulb, motor, or just a resistor, 
should show some sign of activity. The voltmeter 
and ammeter will confirm that you are producing 
power. 
Well done—you have made another great step 
toward the world understanding the hydrogen 
economy and applying it in practice! 
Note 
For a demonstration in an educational setting, the 
Eco H2/O2 system available from Fuel Cell Store 
(see Supplier’s Index) part no. 534407 offers a 
great way to demonstrate the principles in this 
chapter, in a nice, desk-mounted study of solar 
hydrogen electricity. 
169 
Project 46: Stored Hydrogen to Create Electricity 
Figure 17-12 The protons and electrons separate. Figure 17-13 The electrons “do some work.” 
Figure 17-14 The electrons, protons, and oxygen 
are reunited.
Conclusion 
I like to think of fuel cells as a bit like a 
sandwich. If you can, imagine a cheese 
sandwich, with the two pieces of bread as 
the electrodes. Those pieces of bread are buttered. 
It is this butter that effects the interaction between 
the cheese and the bread—the butter can be 
likened to the gas diffusion media. 
The hydrogen economy isn’t something that is 
going to happen overnight. Furthermore, it won’t 
be a single event where all of a sudden we switch 
from one to the other. Instead, hydrogen technologies 
will gradually begin to permeate our lives. 
This will probably start first of all with vehicles 
and portable electronic devices, as these devices 
will benefit from lightweight, high-density energy 
storage that hydrogen affords. We can expect to 
see hydrogen in more and more places. However, 
there are technological hurdles that must be 
overcome first of all. 
Online resources 
This website gives a particularly good animation 
that clearly illustrates what is happening inside a 
PEM fuel cell. 
www.humboldt.edu/~serc/animation.html 
170 Project 46: Stored Hydrogen to Create Electricity 
Figure 17-15 Water is produced. 
Figure 17-16 Circuit diagram.
Photosynthesis—Fuel from the Sun 
Chapter 18 
We can harness solar energy in a lot of different 
direct ways, as we have seen already in this book. 
We can use the sun to meet our requirements for 
heat and electricity. Sometimes, as we saw in 
Chapter 17, we need energy sources that are 
portable and lightweight—for powering cars, for 
example, and for transporting energy to sites where 
it is not appropriate to use solar energy directly. 
One way in which we can harness solar energy, 
is to produce plants that we can turn into fuels. 
Remember, plants use the sun’s energy to grow. 
A plant takes in carbon dioxide from the 
atmosphere, water, and nutrients from the soil, and 
turns it into biological matter. The trees and 
flowers would not exist without the sun’s energy. 
We see in Figure 18-1 the cycle that takes place. 
Some plants can be turned into oils. Remember, 
each time you eat some French fries, they were 
cooked in oil which came from vegetable matter, 
often sunflower. This oil can be burned directly in 
engines. 
It is also possible to turn vegetable oils into a 
product called “biodiesel.” Biodiesel can be used in 
most ordinary diesel engines as if it were any other 
diesel fuel. The difference between the vegetable 
oil, which is a triglyceride, and the biodiesel, is that 
the biodiesel contains shorter hydrocarbon chains. 
This means, that among other properties, the oil is 
less viscous, which means that it flows more freely. 
Another way that we can produce biofuels is to 
produce sugar crops, which can be fermented and 
distilled to produce ethanol. This ethanol can be 
171 
Figure 18-1 Biofuel—fuel from the sun. 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
used in gasoline/petrol engines with relatively little 
modification. 
Countries like Brazil often use a blend of ethanol 
derived from plant matter, and gasoline/petrol from 
conventional sources. This is sold as “Gasohol” in 
many places. By blending the gasoline/petrol with 
ethanol, they are reducing their country’s dependence 
on imported oil. The U.S.A. and many countries 
of the “developed world” can learn a lot from 
these developing countries, as the developed world 
is now largely dependent on imported fuels from 
the Middle East. The oil that is available on “home 
turf” is now largely located in areas of outstanding 
natural beauty, places that are very sensitive to 
environmental change. U.S. oil companies are now 
having to cut pipelines through swathes of Alaska, 
causing enormous environmental damage. Surely 
there are other solutions—solutions that can benefit 
U.S. farmers? 
If we look at how ethanol (Figure 18-2) is 
produced, in Figure 18-3 we can see that the 
process is driven by solar energy. However, it is 
important to note, that at other stages there are 
inputs of energy. These might not always come 
from renewable energy sources, and so it is 
important to be critical and consider how much 
“oil” might be in your biofuel. 
Some farming techniques rely on intensive use 
of fertilizers and other agricultural chemicals—all 
172 Photosynthesis—Fuel from the Sun 
Figure 18-2 A molecule of ethanol—a biofuel 
from the sun. 
Figure 18-3 Ethanol production.
of these require a vast input of energy to manufacture. 
However, there are other farming techniques, 
such as organic farming, which rely on natural, 
low embodied energy techniques. The techniques 
have been honed and refined over hundreds of 
years, and passed down through the ages (remember 
industrialized farming is only a relatively 
recent phenomenon). 
According to C.J. Cleveland of Boston University, 
annual photosynthesis by vegetation in the U.S.A., 
is 4.7 × 1016 Btu, equivalent to nearly 60% of the 
nation’s annual fossil-fuel use. This suggests that 
the amount of plant matter growing is of a similar 
order of magnitude to the amount of energy that 
we consume. It would not be feasible to meet all of 
our energy needs from biofuels, but it certainly 
suggests that they could be used in a wider range 
of applications. 
Coal comes from periods in the world’s history 
when there were lots of trees and plants growing, 
which died, and then were compressed by rocks 
and earth. The carboniferous matter in the coal 
(which means “containing carbon”), is actually 
dead plants. Thus, we can see that coal was also 
produced from solar energy. 
The crucial difference to recognize between 
coal, fossil fuels, and the fuel that we call biomass, 
is that the biomass fuel has recently taken the 
carbon dioxide, which is produced when it burns, 
out of the atmosphere. By contrast, fossil fuels, 
when burnt, are releasing the carbon dioxide which 
was stored under the ground for many millions of 
years. That is why, when we burn fossil fuels, we 
really are creating a massive problem. 
Our ecosystem is a bit like a bucket with a hole 
in it under a tap. The tap is like the carbon dioxide 
we are putting into the atmosphere, and the hole in 
the bucket is like the mechanisms which remove 
carbon dioxide from the air—the plants and 
vegetation which absorb CO2 and release oxygen. 
If we pour water into the bucket at the same rate 
that it flows out, then the level in the bucket stays 
constant. 
Hydrocarbons 
Hydrocarbons are chains of hydrogen atoms and 
carbon atoms. 
173 
Photosynthesis—Fuel from the Sun 
The four hydrogen rule 
Let’s not get too hung up about chemistry here, 
but at the same time, let’s try and understand how 
hydrocarbons work. By now, if you have been 
paying attention, you should realize that atoms of 
carbon and hydrogen combine to form molecules, 
which we call hydrocarbons. This much was 
explained in the “Hydrocarbons” box. However, 
let’s try and understand the rules for the 
combination of hydrogen and carbon atoms. 
A carbon atom has four “sites” where other 
atoms can potentially bond. In the simplest 
hydrocarbon, methane, all four of these sites are 
bonded to hydrogen atoms. We might also know 
this chemical by the name “natural gas.” However, 
in addition to hydrogen atoms, carbon atoms can 
also bond to these sites. 
We can make chains of carbon atoms by 
removing one hydrogen bond from each of two 
methane molecules, and joining the carbons 
together by this “missing” bond. 
We can make these chains longer and longer, 
until eventually we start getting to the point 
where we have eight carbons in a row. When we 
have eight carbons joined by single bonds, we call 
this “octane” and for this level of chemistry, we 
can understand that “octane” is similar to petrol 
or gasoline. If we start adding carbons, we get to 
the point where we have between 10 and 15 in a 
row. The diesel we use in our cars is a mixture of 
10–15 carbon long hydrocarbon chains.
If we are burning mainly biofuels, and replanting 
the things that we burn, then we are only putting 
carbon dioxide into the atmosphere which was 
removed recently. This is like pouring water in at 
the rate it flows out. 
However, if we start turning the tap so that the 
water gushes out, then the level in the bucket 
begins to rise. 
At present, that is what we are doing—we are 
turning up the tap on the carbon dioxide in our 
atmosphere. We are letting it gush out of the tap 
rapidly, with the effect that it is now beginning to 
get to the point where we have more water in the 
bucket than it can hold safely! 
This is because we are putting carbon into the 
atmosphere which was safely tucked away millions 
of years ago. 
If you look at Figure 18-4, you can see that the 
plant is taking in water and carbon dioxide and 
producing oxygen. However, those with some knowledge 
of chemistry must realize that any equation 
must be balanced. Take a peek at Equation 1. 
Here we can see that water and carbon dioxide 
combine to produce glucose and oxygen. The 
glucose is the “food” for the plant that enables it 
to grow. 
A snapshot history 
of biofuel 
Since the earliest days, when an intrepid caveman 
rubbed some sticks together and discovered he 
could warm himself, and finally cook that hot meal 
he had been dying for, we have been burning 
biofuels. Wood has been a staple fuel for heating 
and cooking. 
With the advent of the steam age (the invention 
of the “external combustion engine”), it became 
possible to turn heat into kinetic energy—motion. 
This paved the way for the industrial revolution, 
and brought us mechanized transport in the form 
of early steam vehicles. 
Much of the industrial revolution was powered 
by coal, as it was easy to extract and had a high 
energy density. However, there are also numerous 
examples of steam engines being powered by 
wood fuel. 
This is all very nice . . . but things really start to 
get interesting with the invention of the internal 
combustion engine. This invention can be attributed 
to one Nikolaus August Otto (June 14, 1832– 
January 28, 1891) whose picture you can see in 
Figure 18-5. His idea was pretty revolutionary, and 
really threw the cat amongst the pigeons. Rather 
than burning the fuel “outside” of the cylinder, the 
new idea was to burn the fuel “inside” the cylinder. 
In May 1867, there was a new revolution, the internal 
combustion engine was born. 
You might think that this is bad news for biofuels, 
as it could be tricky squeezing large logs 
inside a small cylinder. Quite the contrary in fact, 
Otto’s original plan was to use ethanol, which 
we have read about in this chapter. Ethanol is a 
biofuel. 
174 Photosynthesis—Fuel from the Sun 
Figure 18-4 Photosynthesis. 
Equation 1 The photosynthesis equation.
Otto’s company is still ticking over nicely and 
now exists under the name Deutz AG. 
In a four-stroke, Otto cycle, internal combustion 
engine, a spark ignites the mixture of fuel and air. 
These are the type of engines you find in petrol or 
gasoline cars. 
However, there is more to the story than that! 
Biofuels got another boost when one Henry Ford 
designed his mass-production “Model T” car to 
run on ethanol! Unfortunately now, our story takes 
a bit of a sinister turn. 
During the Second World War, with supplies of oil 
scarce, countries began to look at using biofuels to 
meet the war-effort’s insatiable demand for energy. 
Unfortunately, after this time biofuels take a bit 
of a turn for the worse. Oil became cheap and 
biofuels disappeared into obscurity . . . until now. 
The western world is now finding it harder than 
ever to find fossil fuels at acceptable prices—both 
financial and environmental. As a result of the 
world’s insatiable lust for oil, areas of outstanding 
natural beauty such as Alaska are being plundered 
for their oil, with dire environmental 
consequences. There is a resurgence of interest in 
biofuel technology—expect to hear much more 
about biofuels in the years to come. 
Bad biofuels? 
Well, all HomeBrewPoweres should be trying to form a 
balanced view of the arguments in the world they 
are trying to conquer. Let’s take a look at the flip 
side of biofuels and assess why, maybe, they aren’t 
going to save the world. 
Biofuels have an important role to play while we 
look for medium-term solutions to our energy 
problems. In the longer term, technologies such as 
the hydrogen economy and hydrogen fuel cells, could 
potentially meet our energy needs. However, in the 
short term, we need to look for transitional solutions 
that will allow us to shift from our “dirty” technologies, 
to more environmentally responsible technologies. 
Biofuels have a part to play in this transition. 
However, if we look at trying to meet all of our 
energy needs from biofuels, it becomes apparent 
that “growing energy” may not be desirable on a 
large scale. There is limited bio-productive land 
(by which we mean land with the ability to 
produce crops) in the world. We need some of this 
land to live on, we need some of this land to 
produce food to eat, and we need some of this land 
for animals to graze. If you do the math, and look 
at a future energy scenario where our needs are met 
by biofuels, you find that it just doesn’t add up. 
With rising populations, and hence rising demand 
for food, and furthermore, rising expectations 
from developing countries, it is apparent that at the 
moment there isn’t enough land to meet our needs 
wholly. 
This doesn’t matter in the short-term, as there is 
plenty of land that is yet to be put to good use, and 
plenty of “biologically derived” waste products of 
industry, that have the potential to provide us with 
energy if we see them as a product rather than 
something to be disposed of. 
175 
Photosynthesis—Fuel from the Sun 
Figure 18-5 Nikolaus August Otto.
Furthermore, we need to look at products that are 
currently treated as waste that could be used to 
provide energy. There are fast-food outlets on every 
block that produce French fries by the million. In 
doing so, they consume copious amounts of vegetable 
oil, which eventually ends up as spent oil to be 
disposed of. Did you know that you can run a diesel 
engine on waste vegetable oil with minimal effort? 
However, while running your vehicle on a waste 
product might be saving the world in your own little 
way, cutting down rainforests to plant fuel crops is 
not. Shamefully, this is what is happening in some 
parts of the world, which sort of defeats the object 
of biodiesel being a more sustainable fuel. 
Vast areas of rainforest are being devastated to 
plant palm oil crops that produce quick oil—and 
money—for the growers. However, for every acre of 
rainforest we lose, we also lose a massive amount of 
biodiversity—and a little bit of the earth’s lungs. 
Moreover, planting large amounts of the same 
thing, isn’t such good news for biodiversity. We need 
a healthy mix of different flora and fauna—having 
large overwhelming amounts of the same thing isn’t 
particularly good for the ecology of the world. 
Photosynthesis 
experiments 
In the following experiments, we will be analyzing 
the solar-driven processes that happen in plants, to 
produce usable products which we can burn as 
biofuels. The process which we have explored 
already, is called “photosynthesis.” 
Sugarcane, rapeseed, and other crops which are 
generally used to produce biofuel are a bit big, 
hard to manage, and unpredictable. For this reason, 
we will be modeling the production of biofuel 
crops using a small, more manageable plant: salad 
cress/mustard. To give you an idea of what you 
should be looking for at the garden center, here are 
the seeds that I used, pictured in Figure 18-6. 
Note 
In order to conduct accurate experiments, we need 
to control all of the variables as closely as we can, in 
order to make sure that our experiments are accurate 
and repeatable. Although it might seem a bit 
pedantic, try and ensure as far as possible that you 
give the plants the amount of water, cotton wool, 
light, etc. as stated in the text. To ensure a fair test, 
try and make sure that all things remain the same. 
For example, if you put several tests on a windowsill, 
ensure that they all receive equal light, and one is 
not in shadow and one in light. 
Watch the book sellers shelves, my forthcoming 
book Convert Your Vehicle to Biodiesel in a 
Weekend will contain details of how you can 
convert a diesel vehicle to run on vegetable oils. 
176 Photosynthesis—Fuel from the Sun 
Figure 18-6 Cress seeds suitable for our experimentation.
You will need 
. 40 salad cress seeds 
. Cotton wool (cotton batting) 
Tools 
. Two small bowls 
. 5 ml measuring syringe 
In this experiment, we are going to test the hypothesis 
that “biofuel requires solar energy in order 
to be produced.” In order to do this, we are going 
to set up two small test cells, which we will use 
to compare the growth of two samples of our 
“biofuel,” cress. 
Take two small bowls. Fill the bottom of one 
with a layer of 2 cm of cotton wool. Carefully pick 
out 20 cress seeds from the packet, and water them 
evenly with 5 ml (5 cm3) of water. We want to 
make our two cells as identical as possible; be as 
accurate as you can, as in order for the test to be 
fair, it must be repeatable. 
One of these bowls should be placed on a bright 
sunny windowsill. The other should be placed on 
the same windowsill but covered with a dark box, 
to prevent any sunlight from reaching the seeds. 
Observe the seeds over several days to see what 
happens. Compare the two samples, but remember 
to cover the “dark” seeds soon after taking a peek. 
Your results should confirm the hypothesis that 
solar energy is required for seeds to grow. 
Of course, we can mimic the properties of sunlight 
using artificial sources of light, but this would seem 
self-defeating as it requires a lot of energy. 
177 
Project 48: Proving Biofuel Requires Water 
Project 47: Proving Biofuel Requires Solar Energy 
Project 48: Proving Biofuel Requires Water 
You will need 
. 40 salad cress seeds 
. Cotton wool 
Tools 
. Two small bowls 
. 5 ml measuring syringe 
This experiment is very similar to the previous one, 
in that we will be comparing two different containers 
of “biofuel crop.” The difference with this experiment 
is that both will be exposed to bright sunlight. 
However, one will receive 5 ml (5 cm3) of water, 
while the other will be on dry cotton wool. 
The results of this experiment should seem 
intuitive—if you don’t water plants, they die; 
however, the experiment is worth carrying out 
nonetheless.
You will need 
. Four identical boxes 
. 80 salad cress seeds 
. Cotton wool 
. Colored filter gelatin red, green, and blue 
Tools 
. Four small identical bowls 
. 5 ml measuring syringe 
We have seen in a previous experiment that for the 
photosynthesis process to occur, light is an essential 
component. We are now going to look at this 
light in a little more detail. 
We are going to set up our cress with the light 
and water that they require. However, this time, we 
are going to have a “control” experiment, and three 
other boxes where the sunlight they receive is filtered 
to “red,” “green,” and “blue.” 
Take four boxes. Fill the bottom of each one 
with a layer of 2 cm of cottonwool. Carefully 
pick out 20 cress seeds from the packet for each 
box, and water them evenly with 5 ml (5 cm3) 
of water. 
You will need to attach a colored gelatin filter 
to the top of three of the boxes, so that the only 
light which reaches the cress seeds is colored. 
Now, compare the growth of the cress seeds. 
What seeds seem to be doing well? Why do you 
think that is? 
Chlorophyll in plants is a “photoreceptor.” It is 
what converts the light from the sun to food for 
plants to grow. In green plants, there are “chloroplasts” 
which contain chlorophyll—these are green 
in color and account for the green coloring of 
plants. 
There are two types of chlorophyll, a and b; they 
both respond to similar wavelengths of light, as 
can be seen in Figure 18-7. 
You will probably find that the red and blue 
filtered plants grew well, whereas the green filtered 
plants did not. If you look at Figure 18-8, you will 
see that the wavelengths where the “peaks” are 
correspond to the wavelengths of blue and red 
colored light. 
The chloroplasts absorb red and blue light, 
but reflect green light—that is why we see plants 
Note 
If you are not sure where to get filters from, ask 
in a good photographic suppliers or stage lighting 
shop for colored gelatin. If this does not work, 
you could always use the clear colored plastic that 
some sweets are wrapped in, carefully joined with 
sticky tape—ensuring that the joins are good and 
no additional light penetrates. 
178 Project 49: Light-Absorption Properties of Chlorophyll 
Project 49: Looking at the Light-Absorption 
Properties of Chlorophyll 
Figure 18-7 Chlorophyll’s response to light.
as green. During the fall/autumn season, the photosynthesis 
activity decreases and the level of chlorophyll 
drops—that is why we see the leaves turn 
from green to reds and orange! 
Biodiesel 
At the moment, our cars run on gasoline and diesel 
from deep oil wells. Because we are fast running 
out of oil, we see the prices steadily creep up. 
Well, what if oil grew on trees. Well, it might not 
grow on trees, but biodiesel certainly comes close! 
Like many of the ideas in this book, it is not a 
new one. Rudolph Diesel, inventor of the diesel 
engine, pictured in Figure 18-9, designed the 
original compression ignition engine (that’s diesel 
engine to you and me) to run on a wide range of 
hydrocarbon fuels. In 1898, Diesel demonstrated 
his engine running on peanut oil! 
We can run compression ignition engines on a 
wide variety of vegetable oils directly, with a little 
modification. However, because these oils are quite 
thick (viscous), problems can be encountered if the 
fuel is cold. For this reason, we take ordinary fuel, and 
turn it into biofuel with a little chemical ingenuity. 
As plants produce their food using 
photosynthesis, biodiesel can be thought of, in a 
way, as “liquid sunshine” solar energy stored in the 
chemical bonds of plants, ready to be used at will. 
Factoid 
Remember that we said plants take in carbon 
dioxide (CO2), and produce oxygen (O2)? Well, 
let’s put some statistics to that assertion! One 
hectare, which is just under two and a half acres, 
of corn, produces enough oxygen to meet the 
requirements of around 325 people! 
179 
Project 49: Light-Absorption Properties of Chlorophyll Figure 18-8 Green light as a component of white light. 
Figure 18-9 Rudolph Diesel.
You will need 
. 100 ml vegetable cooking oil (corn oil, sunflower 
oil, etc.) 
. 20 ml methanol 
. 1 g of lye (sodium/potassium hydroxide) 
Tools 
. Glass lab flask, or cylinder 
. Glass rod to mix 
. Hydrometer 
. Safety equipment 
. Eye wash 
. Goggles 
. Gloves 
. Apron 
. Vinegar 
In this experiment, we are going to be making 
biodiesel, a fuel that will run in diesel engines, produced 
from biological matter, in this case vegetable 
oil. It is possible to run an ordinary diesel vehicle 
on biodiesel as can be seen in Figure 18-10. Some 
environmentally responsible companies are beginning 
to run fleets of vehicles on biodiesel. 
Increasingly, we are seeing blends of biodiesel and 
petro-diesel being sold on garage forecourts, and in 
If you want to know where to get methanol 
from, try a good modeller’s shop—as it is often 
sold as a fuel for model plane engines. 
Warning 
Because of the methanol and the lye used in this 
experiment (both of which are toxic and not nice 
to handle) this experiment should be carried out 
under the supervision of a responsible adult. Lye 
is a really strong alkali, which can cause chemical 
burns if you are not careful. If you get the dust in 
your eye, it can cause permanent damage, even 
blindness. You may think that it is an unusual 
inclusion for a safety list, but in the event of 
spilling any lye, put a spot of vinegar on the lye 
to neutralize it and make it safe. The acid will 
react with the alkali and produce carbon dioxide. 
Make sure you wear all the safety equipment 
above and take sensible precautions. 
If you are wondering where to get lye from, it 
is commonly sold as caustic drain cleaner, but be 
aware, it is nasty stuff so take safety precautions. 
180 Project 50: Make Your Own Biodiesel 
Project 50: Make Your Own Biodiesel 
Figure 18-10 Filling a car with biodiesel.
some cases, small quantities of biodiesel are being 
added to ordinary diesel as a lubricant. 
In this project, we are going to make a small 
quantity of biodiesel. This experiment aims to 
show the process, and illustrate a little bit of the 
chemistry of manufacturing biodiesel. However, 
please note that there is very little “quality control” 
in this experiment, so it would be unwise to use 
the produced biodiesel in a diesel engine. 
First take the vegetable oil and heat it up to 
over 100°C to ensure that any water is driven off. 
Be careful not to overheat. 
In a separate container, thoroughly mix the 
methanol and lye. This forms a mixture that 
biodiesel home brewers call “methoxide,” you 
need to be very careful during this stage as it 
entails using some very nasty chemicals. 
Now add the methoxide to the vegetable oil. 
Try and do this at around 45°C for the best 
reaction. 
Be careful not to breathe in any of the methanol 
vapors. If you have access to a fume cupboard in a 
school chemistry department, then use that for 
safety. If not, just make sure you are in a wellventilated 
area—outside for example. 
Make sure that you thoroughly stir the mixture 
for a few minutes. 
Now, put the container somewhere safe, out of 
the reach of small children, and allow the mixture 
to settle overnight. 
When you next look at the mixture, you should 
see that it has settled into two distinct layers. At 
the bottom of the container will be a brown goo. 
This is a mixture of glycerol, unused methanol, 
and catalyst, and possibly a little soap, which 
will be the product of any fatty acids in the oil to 
begin with. 
The layer on top is our biodiesel! Again, I 
reiterate the earlier warning—do not put this in 
your vehicle. It will probably work, but this 
particular biodiesel has been made with no quality 
control, so there is a high possibility that it could 
damage your engine. 
Testing your biodiesel 
The first test that you will need to conduct is a 
visual inspection—what does your biodiesel 
look like? 
Well, there should be a clear visual distinction 
between the top layer and the bottom layer in your 
measuring container. If there is a large intermediate 
layer of soaps, then the chances are that you 
did not remove sufficient water from the oil to 
begin with. 
You may be able to get a piece of equipment 
called a “hydrometer.” A hydrometer will tell you 
the density of a fluid. Your biodiesel should check 
out with a density of between 880 and 900 grams 
per liter. 
Biodiesel chemistry 
So what have we done in this little experiment? 
If you look at Figures 18-11 and 18-12, you will 
see that we have what is called a “triglyceride” 
molecule. This is the vegetable oil that we start 
off with. We can represent this using a “ball and 
stick” model, which shows us the position of the 
atoms in 3D space, or we can show the chemistry 
using a “structural formula” such as that shown in 
Figure 18-12. 
You will notice when looking at the structure of 
the triglyceride that there are three long “chains” 
of hydrocarbons (hence the ‘tri’ bit) and a “bacbone,” 
Online resources 
If you want to make biodiesel, you might be 
interested in the following web resources, which 
contain information on manufacturing biodiesel. 
www.schnews.org.uk/diyguide/howtomake 
biodiesel.htm 
www.veggiepower.org.uk/ 
journeytoforever.org/biodiesel_make.html 
181 
Project 50: Make Your Own Biodiesel
182 Project 50: Make Your Own Biodiesel 
Figure 18-11 Ball and stick model of a triglyceride. 
Figure 18-12 Structural formula of a triglyceride.
which links up the three hydrocarbon chains. This 
backbone breaks off from the chains to form 
“glycerol,” and this accounts for the “glyceride” bit 
of the name. 
Our methoxide mixture which was added to our 
triglycerides catalyzed a reaction where the three 
chains broke off from the backbone. The glycerol 
backbone is heavy, so settles to the bottom of the 
jar, whereas the lighter hydrocarbon chains float to 
the top of the jar—and it is these which form our 
“biodiesel.” 
Why do we separate the chains from the glycerol 
backbone? Well, the structure of the triglyceride 
means that it can easily become “tangled up” with 
other triglyceride molecules, which results in a 
thick viscous oil. The chains on their own, are a lot 
shorter and so tangle less easily, and as a result, 
are less viscous. This brings with it a whole host of 
other desirable properties, which means that the 
fuel can flow freely in a diesel engine without 
clogging up the injectors. 
183 
Project 50: Make Your Own Biodiesel
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Solar Projects on the Web 
Appendix A 
Hopefully, this book has provided an interesting 
primer on solar energy. I rather hope that I have 
empowered you with the tools to go onwards and 
create your own solar inventions, powered by clean 
green energy. To help you on your way, and 
provide inspiration, I have compiled a list of 
projects, articles, and inspirational solar tech 
stories that I have rooted out for you on the web. 
This should provide creative inspiration for your 
own sustainably powered designs. All of these sites 
seem to be particularly interesting or quirky—this 
highlights the need to be creative when finding 
applications for technologies, rather than being 
constrained by the dogma of existing applications. 
I truly hope they will inspire you, the reader, to go 
out there and create something truly unique. 
Want Java? Go Solar 
I’ve seen it all now—a solar-powered coffee 
roaster! Clean energy when used with fair-trade 
coffee makes for a guilt-free expresso. 
www.makezine.com/blog/archive/ 
solar_roast_coffee.jpg 
www.solarroast.com/home.html 
Solar-Powered Wiggly Sign 
In this fantastic site, engineer and cartoonist Tim 
Hunkin builds an interesting piece of kinetic 
sculpture, powered by the sun. 
www.timhunkin.com/a125_arch-windpower.htm 
Humungous Solar-Powered Laundry 
The world’s biggest laundry employs solar power! 
Read all about how clothes are being washed 
without the negative environmental connotations at 
USA Today. 
www.usatoday.com/tech/news/techinnovations/ 
2006-07-30-solar-laundromat_x.htm?csp=34 
Solar-Powered Wheelchair 
Bob Triming introduces us to his clean green form 
of transport—a solar-powered wheelchair. Flat 
batteries are a thing of the past. 
www.infolink.com.au/articles/63/0C044763.aspx 
Villages in Tanzania Use Solar Power to 
Sterilize Water 
Here is an example of the solar still technology 
seen in this book in action. Villagers are using it to 
purify their water and prevent illness in Africa. 
news.bbc.co.uk/1/hi/world/africa/4786216.stm 
Solar Clothing Monitors Medical 
Conditions 
Certainly not the coolest looking jacket on the 
block, this solar-powered item of clothing monitors 
medical conditions by using inbuilt sensors. 
Hopefully, you won’t feel ill in the dark. 
www.digitalworldtokyo.com/2006/09/ 
taiwan_puts_ehealth_solar_pane.php 
Solar-Powered iPod Shuffle 
Powered by a flexible solar cell, Make: show how 
to convert an iPod shuffle to run on green power. 
www.makezine.com/blog/archive/2005/03/ 
solar_powered_i.html 
Massive Parabolic Solar Death Ray 
This death ray was built for cooking hot dogs at 
the Burning Man event. The scale of this thing is 
totally immense! It is well worth a look. 
igargoyle.com/archives/2006/07/solar_death_ray_ 
for_hot_dogs.html 
MIT Solar Generator from Car Junk 
In trying to invent a low-cost form of solar energy, 
these academics at the Massachusetts Institute of 
185 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
Technology showcase their solar generator from 
old auto junk. Recycled green power! 
www.technologyreview.com/read_article.aspx?id= 
17169&ch=biztech 
Solar Water Warmer 
A simple and inexpensive design for a solar 
water heater. Brought to you by Mother 
Earth News. 
http://www.motherearthnews.com/library/ 
1979_September_October/ 
A_Homemade_Solar_Water_Heater 
Sun-Powered Tunes 
Listen to some music while not having the guilt 
of carbon emissions! A solar-powered boom 
box—because let’s face it, who wants a party on 
an overcast day? 
www.makezine.com/blog/archive/2006/05/ 
homemade_solar_powered_boombox.html 
Solar Sunflower 
This ’bot, which is essentially a solar tracker, 
follows the sun in the same way as sunflowers do. 
Don’t water it though! 
www.instructables.com/id/ 
E8UMC79GJAEP286WF5/ 
Organic LEDs Generate Power 
Organic LEDs—a term you are going to hear 
about a lot more in the future! As well as 
producing light from electricity, these clever little 
gadgets also have the potential to produce power 
from light. 
www.ecogeek.org/content/view/242/ 
Solar Scooter Provides Sustainable 
Transport 
A home-built solar-powered scooter, which during 
a last look at its odometer had clocked up near to 
1,000 miles. Scoot on! 
www.treehugger.com/files/2005/09/ 
diy_eco-tech_ti.php 
Solar Networking 
Interesting article about solar-powered wireless 
networking in Boulder, Colorado! Is this the 
future of the Internet? 
www.internetnews.com/wireless/article. 
php/3525941 
Solar Death Ray 
Another solar death ray, with a cool gallery of 
burnt stuff! Remember kids, if you toast your 
siblings, your parents may get mad at you. 
In addition, note the obligatory: “Do not stare 
into the beam directly.” 
www.solardeathray.com/ 
Solar Bike Light 
Bicycles are already a nice sustainable method 
of transport that do not chuck plumes of carbon 
dioxide into the air. Well, go one step further, 
rather than powering your lights from batteries 
that go in the bin, build a solar-powered bike light. 
Genius! 
www.creekcats.com/pnprice/Bike05-Pages/ 
bikelight.html 
Solar Greenhouse 
A nice page about the joys of adding a solar 
greenhouse to the side of a dwelling. 
www.theworkshop.ca/energy/grnhouse/ 
grnhouse.htm 
Solar-Powered Handbag 
One for the girls, a solar-powered handbag, 
designed by a smart student from Brunel 
University, U.K. The solar panel charges a 
battery, which powers a lining, which glows 
when the bag is opened. Never lose your keys 
again! Louis Vuitton nothing! 
news.bbc.co.uk/2/hi/technology/4268644.stm 
Passive Solar Collector 
A nice passive solar collector made from wholly 
recycled materials. 
www.theworkshop.ca/energy/collector/collector.htm 
186 Solar Projects on the Web
Solar Ant-Zapper 
Possibly cruel (that’s my disclaimer to avoid letters 
from the American Humane Association) but this 
solar-powered ant-zapper could be the answer to 
your infestation woes. 
www.americaninventorspot.com/ 
backyard_solar_energy 
Organic Solar Cells Based on Biological 
Mechanisms 
We read in Chapter 18 all about the process of 
photosynthesis, but how about organic solar cells 
which mimic the processes that plants use to 
produce energy. Interesting! 
www.abc.net.au/science/news/stories/s1729572.htm 
Honda Prius Supplements Power with Solar 
A modified Honda Prius, which uses solar power 
to supplement the juice in the car’s batteries to 
bring an increase in economy! 
www.treehugger.com/files/2005/08/ 
solar-powered_t.php 
Solar-Powered Light Graffiti 
For miscreants who like to tag, here is the perfect 
substitute, which does no damage, and uses clean 
renewable energy to make its mark. 
rdn.cwz.net/archives/17 
Holographic Solar Cells 
Read about holographic solar cells, which use a 
holographic optical element to concentrate the 
frequencies that matter! 
www.prismsolar.com/ 
Top 10 Strangest Solar Gadgets 
This blog provides some interesting thoughtprovoking 
ideas—the top 10 strangest solar 
gadgets. Will you invent number 11? 
www.techeblog.com/index.php/tech-gadget/ 
top-10-strangest-solar-gadgets 
Solar Ferry for Hyde Park 
A solar-powered ferry for the Serpentine in Hyde 
Park, London, U.K. How novel! Forty-eight foot 
long with 27 panels on its roof. 
www.usatoday.com/tech/science/ 
2006-07-18-solar-ferry_x.htm?csp=34 
Solar-Powered Backpack 
Charge your laptop with the power of the sun 
while trekking up Everest! Now we have heard it all 
www.rewarestore.com/product/020010003.html 
Sun Bricks 
An interesting concept, solar-powered bricks that 
incorporate light emitting diodes to provide 
illumination at night—a novel idea! 
www.gardeners.com/on/demandware.store/Sites- 
Gardeners-Site/default/ViewProductDetail- 
SellPage?OfferID=35-945&SC=xnet8102 
Proposed Solar Chimney Down Under 
This massive solar chimney has been proposed to 
generate power in Australia, using a large 
greenhouse to heat air, and a solar thermally driven 
process. All of 1,600 ft tall! 
money.cnn.com/2006/08/01/technology/ 
towerofpower0802.biz2/index.htm?cnn=yes 
www.enviromission.com.au/project/technology.htm 
Nanosolar—Printed Solar Cells 
If Google founders Larry Page and Sergey Brin 
stick their cash here, you can bet that it is big 
business. Nanosolar are a new venture who aim to 
produce lots of cheap solar cells using simple 
printing technology. 
nanosolar.com/index.html 
187 
Solar Projects on the Web
Supplier’s Index 
Appendix B 
Miscellaneous 
Alternative Energy Hobby Store 
Dennis Baker 
49732 Chilliwack Central RD 
Chilliwack BC, V2P 6H3 
Canada 
Tel: 1-604-819-6353 
Fax: 1-604-794-7680 
Dennis@AltEnergyHobbyStore.com 
www.altenergyhobbystore.com/ 
Education_solar_books.htm 
Arizona Solar Center 
c/o Janus II—Environmental Architects 
4309 E. Marion Way 
Phoenix AZ 85018 
USA 
solar@azsolarcenter.com 
www.azsolarcenter.com/bookstore/reviews.html 
Centre for Alternative Technology Mail 
Order 
Machynlleth 
Powys 
SY20 9AZ 
UK 
Kentucky Solar Living 
Tel: 1-859-200-5516 
kentuckysolar@ipro.net 
Silicon Solar 
Direct Sales 
Tel: 1-800-653-8540 (Mon–Fri 8 am–4 pm EST) 
Fax: 1-866-746-5508 
Tampa Bay, FL 
Tel: 1-727-230-9995 
Fort Worth, TX 
Tel: 1-817-350-4667 
San Diego, CA 
Tel: 1-858-605-1727 
www.siliconsolar.com/solar-books.php 
Solar Electric Light Fund 
1612 K Street, NW Suite 402 
Washington DC 20006 
USA 
Tel: 1-202-234-7265 (8:30 am–6 pm EST) 
info@self.org 
www.self.org/books.asp 
Drinking birds for solar engines 
The Drinking Bird 
Tel: 1-800-296-5408 
www.thedrinkingbird.com/ 
HobbyTron.com 
1053 South 1675 West 
Orem UT 84058 
USA 
Tel: 1-801-434-7664 
Toll-free: 1-800-494-1778 
www.hobbytron.com/.html 
Niagara Square 
7555 Montrose Road 
Niagara Falls ON, L2H 2E9 
Canada 
Tel: 1-905-354-7536 
Fax: 1-905-354-7536 
188 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
189 
Supplier’s Index 
Science eStore 
5318 E 2nd Street #530 
Long Beach CA 90803 
USA 
http://www.physlink.com/eStore 
1-888-438-9867 
11am -8pm EST 
Electronic components for the 
projects in this book 
Electromail/RS Components 
RS Components Ltd 
Birchington Road, Corby 
Northants NN17 9RS 
UK 
Orderline: 44-(0)-8457-201201 
www.rswww.com 
Maplin Electronics Ltd 
National Distribution Centre 
Valley Road 
Wombwell, Barnsley 
South Yorkshire S73 0BS 
UK 
www.maplin.co.uk 
Radio Shack 
300 RadioShack Circle 
MS EF-7.105 
Fort Worth TX 76102 
USA 
Tel: 1-800-843-7422 
Rapid Electronics Ltd 
Severalls Lane 
Colchester 
Essex CO4 5JS 
UK 
Tel: 44-(0)-1206-751166 
Fax: 44-(0)-1206-751188 
sales@rapidelec.co.uk 
www.rapidelectronics.co.uk/ 
Fresnel lenses and parabolic 
mirrors 
Alltronics 
PO Box 730 
Morgan Hill CA 95038-0730 
USA 
Tel: 1-408-778-3868 
www.alltronics.com 
Anchor Optical Surplus 
101 East Gloucester Pike 
Barrington NJ 08007-1380 
USA 
Fax: 1-856-546-1965 
Edmund Optics Inc. 
101 East Gloucester Pike 
Barrington NJ 08007-1380 
USA 
Tel: 1-800-363-1992 
Fax: 1-856-573-6295 
Science Kit & Boreal Laboratories 
777 E. Park Drive 
PO Box 5003 
Tonawanda NY 14150 
USA 
Tel: 1-800-828-7777 
Fax: 1-800-828-3299 
www.sciencekit.com 
TEP 
International Manufacturing Centre 
University of Warwick 
Coventry CV4 7AL 
UK 
Inverters and power 
regulators 
Omnion Power Engineering 
2010 Energy Drive 
PO Box 879
190 Supplier’s Index 
East Troy WI 53120 
USA 
Tel: 1-262-642-7200 or 1-262-642-7760 
www.sandc.com/omnion/home.htm 
Real Goods 
360 Interlocken Blvd, Ste 300 
Broomfield CO 80021-3440 
13771 So. Highway 101 
PO Box 836 
Hopland CA 95449 
USA 
Tel: 1-800-919-2400 
www.realgoods.com 
Photochemical solar cell 
components 
ICE, the Institute for Chemical Education 
University of Wisconsin-Madison 
Department of Chemistry 
1101 University Avenue 
Madison WI 53706-1396 
USA 
Tel: 1-608-262-3033 or 1-800-991-5534 
Fax: 1-608-265-8094 
ICE@chem.wisc.edu 
Photovoltaic cells for buildings 
Flagsol 
Flachglas Solartechnik GmBH 
Muhlengasse 7 
D-50667 Cologne 
Germany 
Tel: 49-(0)-221-257-3811 
Fax: 49-(0)-221-258-1117 
Schüco International 
Whitehall Avenue, Kingston 
Milton Keynes MK10 0AL 
UK 
Tel: 44-(0)-1908-282111 
Fax: 44-(0)-1908-282124 
Photovoltaic modules 
Advanced Photovoltaics Systems 
PO Box 7093 
Princeton 
NJ 08543-7093 
USA 
Tel: 1-609-275-0599 
BP Solar International 
PO Box 191, Chertsey Road 
Sunbury-on-Thames 
Middlesex TW16 7XA 
UK 
Tel: 44-(0)-1932-779543 
Fax: 44-(0)-1932-762533 
Kyocera 
8611 Balboa Avenue 
San Diego CA 92123 
USA 
Tel: 1-619-576-2647 
Siemens Solar Industries 
PO Box 6032 
Camarillo CA 93010 
USA 
Tel: 1-805-698-4200 
Solarex Corporation 
630 Solarex Court 
Fredrick MD 21701 
USA 
Tel: 1-301-698-4200 
Solec International 
52 East Magnolia Boulevard 
Burbank CA 91502 
USA 
Tel: 1-213-849-6401
191 
Supplier’s Index 
Solar array structures, mounting 
hardware 
Kee Industrial Products Inc. 
100 Stradtman Street 
Buffalo NY 14206 
USA 
Tel: 1-716-896-4949 
Toll-free: 1-800-851-5181 
Fax: 1-716-896-5696 
info@keeklamp.com 
Kee Klamp GmbH 
Voltenseestrasse 22 
D-60388 Frankfurt/Main 
Germany 
Tel: 49-(0)-6109-5012-0 
Fax: 49-(0)-6109-5012-20 
vertrieb@keeklamp.com 
Kee Klamp Limited 
1 Boulton Road 
Reading 
Berks RG2 0NH 
UK 
Tel: 44-(0)-118-931-1022 
Fax: 44(0)-118-931-1146 
sales@keeklamp.com 
Leveleg 
8606 Commerce Ave 
San Diego CA 92121-2654 
USA 
Tel: 1-619-271-6240 
Poulek Solar Ltd 
Velvarska 9 
CZ-16000 Prague 
Czech Republic 
Tel: 42-(0)-603-342-719 
Fax: 42-(0)-224-312-981 
www.solar-trackers.com 
Science Connection 
50 East Coast Road, #02-57 
Singapore 428769 
Tel: 65-65-68966 
Fax: 65-623-44589 
www.scienceconnection.com/Tech_advanced.htm 
Wattsun 
Array Technologies Inc. 
3312 Stanford NE 
Albuquerque NM 87107 
USA 
Tel: 1-505-881-7567 
Fax: 1-505-881-7572 
sales@wattsun.com 
www.wattsun.com 
Zomeworks 
PO Box 25805 
1011A Sawmill Road 
Albuquerque NM 87125 
USA 
Tel: 1-800-279-6342 or 1-505-242-5354 
Fax: 1-505-243-5187 
zomework@zomeworks.com 
Solar controllers/temperature 
monitors/instrumentation 
HAWCO Ltd, Industrial Sales 
The Wharf, Abbey Mill Business Park 
Lower Eashing 
Surrey GU7 2QN 
UK 
Tel: 44-(0)-870-850-3850 
Fax: 44-0)-870-850-3851 
sales@hawco.co.uk 
Raydan Ltd. 
The Sussex Innovation Centre 
Science Park Square 
Falmer, Brighton 
Sussex BN1 9SB 
UK 
Tel: +44-(0)-1273-704442 
Fax: +44-(0)-1273-704443 
sales@raydan.com
192 Supplier’s Index 
Solar pool-heater manufacturers 
Heliocol 
13620 49th Street North 
Clearwater FL 33762 
USA 
Tel: 1-727-572-6655 or 1-800-79-SOLAR 
(1-800-797-6527) 
http://www.heliocol.com/ 
Imagination Solar Limited 
10–12 Picton Street 
Montpelier 
Bristol BS6 5QA 
UK 
Tel: 44-(0)-845-458-3168 
Fax: 44-(0)-117-942-0164 
enquiries@imaginationsolar.com 
Solar Industries Solar Pool Heating 
Systems 
1940 Rutgers University Boulevard 
Lakewood NJ 08701 
USA 
Tel: 1-800-227-7657 
Fax: 1-732-905-9899 
www.solarindustries.com/ 
Solar Twin Ltd 
2nd Floor, 50 Watergate Street 
Chester CH1 2LA 
UK 
Tel: 44-(0)-1244- 403407 
hi@solartwin.com 
http://www.solartwin.com/pools.htm 
Solar robotics supplies 
Solarbotics Ltd 
201 35th Ave NE 
Calgary AB, T2E 2K5 
Canada 
Tel: 1-403-232-6268 
N. America toll-free: 1-866-276-2687 
Places to get more information 
American BioEnergy Association 
314 Massachusetts Avenue, NE 
Suite 200 
Washington DC 20002 
USA 
www.biomass.org 
American Council for an Energy Efficient 
Economy 
1001 Connecticut Avenue, Suite 801 
Washington DC 20036 
USA 
www.aceee.org 
American Solar Energy Society (ASES) 
2400 Central Avenue, Suite G-1 
Boulder CO 80301 
USA 
Tel: 1-303-442-3130 
Fax: 1-303-443-3212 
ases@ases.org 
www.ases.org 
California Energy Commission 
1516 Ninth Street 
Sacramento CA 
USA 
Tel: 1-958-145-512, 1-800-555-7794, or 
1-916-654-4058 
www.energy.ca.go 
Center for Excellence in Sustainable 
Development 
US Department of Energy, Denver Regional Office 
1617 Cole Boulevard 
Golden CO 80401 
USA 
Fax: 1-302-275-4830 
Energy Efficiency and Renewable Energy 
Clearinghouse (EREC) 
PO Box 3048 
Merrifield VA 22116
193 
Supplier’s Index 
USA 
Tel: 1-800-DOE-EREC or 1-800-363-3732 
Fax: 1-703-893-0400 
Doe.erec@nciinc.com 
Florida Solar Energy Center (FSEC) 
1679 Clearlake Road 
Cocoa FL 32922 
USA 
Tel: 1-407-638-1000 
Fax: 1-407-638-1010 
info@fsec.ucf.edu 
www.fsec.ucf.edu 
Home Power Magazine 
PO Box 520 
Ashland OR 97520 
USA 
Tel: 1-800-707-6585 
www.homepower.com 
NASA Earth Solar Data 
eosweb.larc.nasa.gov/sse/ 
National Biodiesel Board 
3337a Emerald Lane 
PO Box 104898 
Jefferson City MO 65110-4898 
USA 
National Center for Appropriate Technology 
3040 Continental Drive 
Butte MT 59701 
USA 
Tel: 1-406-494-4572 
National Renewable Energy Laboratory 
1617 Cole Boulevard 
Golden CO 80401-3393 
USA 
Tel: 1-303-275-3000 
webmaster@nrel.gov 
www.nrel.gov 
North Carolina Solar Center 
Box 7401 
North Carolina State University 
Raleigh NC 27695-7401 
USA 
Tel: 1-800-33-NCSUN 
Fax: 1-919-515-5778 
ncsun@ncsu.edu 
www.ncsc.ncsu.edu 
Northeast Sustainable Energy Association 
50 Miles Street 
Greenfield MA 01301 
USA 
Rocky Mountain Institute 
1739 Snowmass Creek Road 
Snowmass CO 81654-9199 
USA 
Sandia National Laboratory—California 
PO Box 969 
Livermore CA 94551 
USA 
Tel: 1-925-294-2447 
Sandia National Laboratory—New Mexico 
PO Box 5800 
Albuquerque NM 87185 
USA 
Tel: 1-505-844-8066 
webmaster@sandia.gov 
www.sandia.gov 
Solar Electric Light Fund 
1612K Street NW, Suite 402 
Washington DC 20006 
USA
194 Supplier’s Index 
Solar Energy Industries Association 
1111 N. 19th Street 
Suite 260 
Arlington VA 22209 
USA 
Tel: 1-703-248-0702 
Fax: 1-703-248-0714 
info@seia.org 
www.seia.org/Default.htm 
Solar Energy International 
PO Box 715 
Carbondale CO 81623 
USA 
Tel: 1-970-963-8855 
Fax: 1-970-963-8866 
sei@solarenergy.org
AC (alternating current), 100, 102, 102 
air conditioning, 39, 41 
albedo radiation, 99, 99 
alternating current (AC), 100, 102, 102 
Archimedes, 61 
BEAM (Biology, Electronics, Aesthetics, and Mechanics) 
robotics, 150, 159. See also solar robotics 
Becquerel, Edmund, 81 
biodiesel, 13, 171, 176, 179–181, 183 
biofuel, 171–173, 171, 172, 174–177, 179–181 
limitations of, 175–176 
biomass, 6, 6, 13, 38, 173. See also biofuel 
biomimickry, 105 
carbon dioxide, 3, 173–174 
sequestration, 167 
chlorophyll, 178–179, 178 
climate change, 5 
coal, 2–3, 34, 66, 173, 174. See also carbon dioxide 
collector. See solar collector 
compression ignition engine, 179 
cooking, 1, 1. See also solar cooking 
DC (direct current), 100, 102, 102–103 
Diesel, Rudolph, 179, 179 
diesel engine, 176, 179. See also biodiesel 
direct current, 100, 102, 102–103 
Einstein, Albert, 81 
electrical power, 1, 34. See also hydro-electric power; 
hydrogen economy; nuclear power; photochemical 
solar cell(s); solar photovoltaic cell(s); 
wind power 
electricity. See electrical power 
energy 
consumption, domestic, 1, 1 
non-renewable sources of (see fossil fuels) 
nuclear (see nuclear power) 
solar (see solar energy) 
See also hydro-electric power; hydrogen economy; nuclear 
power; photochemical solar cell(s); solar photovoltaic 
cell(s); wind power 
ethanol, 171–173, 172, 174–175 
fossil fuels, 2 
emissions, 2–3, 4 
and energy in the U.S., 7 
sources of, 2–3, 5, 6, 15 
See also carbon dioxide; Hubbert’s Peak theory; Peak Oil 
Fresnel lens, 72–73, 72, 73 
sources, 72–73, 189 
See also solar concentrator 
Fritts, Charles, 81 
fuel cell, 161–162, 163, 164–165, 165 
mechanics of, 162–164, 168–170, 168, 169, 170 
types of, 162, 163 
Gasohol, 172. See also ethanol 
Gratzel, Michael, 105 
heating 
of food (see solar cooking) 
solar (see solar heating) 
space, 1, 1 (see also solar heating) 
of water, 1, 1 (see also solar heating: for hot water) 
heliodon, 22–25, 24, 25, 26 
Hubbert’s Peak theory, 3–4, 4 
hydrocarbon, 2, 171, 173 
hydro-electric power, 6, 6, 7–8, 13 
hydrogen, generation of, 164–167. See also hydrogen economy 
hydrogen economy, 161–162, 168–170 
hydrological cycle, 55, 55 
hydropower. See hydro-electric power 
industrial revolution, 3, 149, 174 
internal combustion engine, 174–175 
fuel cells vs., 162 
See also steam engine 
International Energy Agency, 4 
inverter, 102, 102 
Mouchot, Augustin, 8, 55, 66, 67 
nuclear power, 4–5, 7, 7 
Ohl, Russell, 81 
195 
Index 
Page numbers for tables and figures are given in bold 
Copyright © 2007 by The HomeBrewPower Companies, Inc. Click here for terms of use.
Otto, Nikolaus, 174–175, 175 
oxygen, from plants, 174, 179. See also photosynthesis 
Peak Oil, 3–4, 4 
photobiological solar cell(s), 111 
photochemical solar cell(s), 105–110, 106 
future of, 110 
limitations of, 110 
photosynthesis, 38, 171–174, 171, 172, 174, 176–179 
production of hydrogen by, 167 
photovoltaics. See solar photovoltaic cell(s) 
Project Ingenhousz, 111 
seasons, 12, 12, 13, 17, 19, 19, 21–22 
sequestration, 167 
silicon, 82, 83, 82, 84, 85–86, 86. See also solar 
photovoltaic cell(s): crystalline 
solar battery charger, 119–120, 120 
solar cell 
photobiological, 111 
photochemical (see photochemical solar cell(s)) 
photovoltaic (see solar photovoltaic cell(s)) 
solar clock, 17, 18, 20–21 
solar collector, 61, 186 
angle of sun and, 25–26 
evacuated tube, 30, 30 
flat plate, 27, 30–32, 30, 31, 32, 33, 129 (see also solar tracker) 
See also solar concentrator 
solar concentrator, 61, 62, 63, 64, 64–66, 65, 66 
Fresnel lens, 72–74, 74 
parabolic dish, 66–67, 67, 68, 69–70, 70, 71 
See also solar death ray 
solar cooker, 50–53, 51 
camping stove, 51–52, 52 
coffee roaster, 185 
hot dog, 46–47, 47, 185 
marshmallow melter, 48, 48 
solar cooking, 45, 45, 49, 49, 52–54 
recipes for, 53–54 
See also solar cooker 
solar cooling 
active, 41–44, 43, 44 
passive, 39–41 
solar death ray, 61, 63, 64–66, 185, 186 
solar distillation. See solar still 
solar-driven energy. See biomass; hydro-electric power; wave 
power; wind power 
solar energy 
advantages of, 2, 5 
capturing, 14, 15, 17, 19–22, 25–26 (see also solar-driven energy) 
devices (see solar energy: capturing) 
limitations of, 161 
in the U.S., 2, 7, 34, 186 
solar engines, 113–116, 116, 117, 118, 139 
solar garden light, 127–128, 128 
solar heating, 27–28 
circuits for, 35–37, 36 
future of, 37–38 
solar heating (cont.) 
of homes, 28 
for hot water, 28–29, 29 
passive, 28 
for power generation, 34, 35 
roof panels (see solar collector: flat plate) 
of swimming pools, 33–34, 34 
solar ice-maker, 42–43, 43, 44 
solar panel. See solar collector: flat plate 
solar phone charger, 120–122, 122 
solar photovoltaic cell(s), 81, 105 
current-voltage characteristics, 92–94, 92, 93, 94 
crystalline, 82–87, 82, 83, 84 
for driving pumps, 29, 75, 75, 79 
and homes, 100, 101, 102–103 
light sources and, 94–99, 95, 96, 97, 98, 99 
thin-film, 83, 83, 87–91, 91 
solar pump, 75–79, 76, 78 
solar radio, 123–124, 123, 124 
solar robotics, 150, 151, 152, 152–159 
solar still, 55–59, 56, 57, 58, 59, 185 
solar torch, 124–125, 125, 126 
solar tracker, 129–132, 129, 130, 131, 132, 133 
solar transport 
aviation, 145, 146, 146–148, 147, 148 
cars, 136–143, 136, 137, 138, 186 
ferry, 187 
scooter, 186 
wheelchair, 185 
solar warning light, 126–127, 127 
steam engine, 113, 174 
steam reforming, 167 
sun, 9, 9–10 
and the earth, 12, 12, 17–21 
energy from (see solar energy) 
structure of, 10, 10–11 
surface of, 11, 11–12 
See also photosynthesis; solar heating 
sundial. See solar clock 
thermosiphon, 28, 35 
tidal power, 7, 13 
titanium dioxide, 105, 107 
transportation, 135. See also solar transport 
triglyceride, 181, 182 
Trombe wall, 39–40, 40, 41 
United States 
energy sources, 2, 7, 7 
solar energy in, 2, 7, 34, 186
water 
distillation of (see solar still) 
pumping of (see solar pump) 
wave power, 6, 7, 13 
wind energy, 6, 6–7, 13 
wind power, 6, 6–7, 13 

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