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04 November, 2008

Solar Energy Projects

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

New York Chicago San Francisco Lisbon London Madrid

Mexico City Milan New Delhi San Juan Seoul

Singapore Sydney Toronto

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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

Foreword

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.

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.

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

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.”

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.

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

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.

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.

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.

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.

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

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.”

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.

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

. Craft knife

. Protractor

For the wooden heliodon

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

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

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.

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

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

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.

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.

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.

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

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

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

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

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.

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.

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,

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.

Figure 5-5 The solar cooler cycle.

Project 7: Solar-Powered Ice-Maker

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!

Figure 6-1 A solar cooker being used in the

developing world. Image courtesy Tom Sponheim.

You will need

. Small photovoltaic cell

. Flexible acrylic mirror

. Elastic band and pulley wheel

. Small plastic worm gear and large plastic

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!

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

Project 8: Build a Solar Hot Dog Cooker Figure 6-2 Solar hot dog cooker.

Figure 6-3 Drive mechanism.

. 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

. 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

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

. 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!

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

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

Solar Cooking in the Peruvian Andes

www.sunspot.org.uk/Solar.htm

Solar cooking in the developing world

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

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.

Figure 7-1 The hydrological cycle.

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

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!

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

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

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.

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!

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.

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

. Hand/cordless drill

. Glue gun and sticks

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

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.

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

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.

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

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/

. 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.

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:

Chapter 9

Solar Pumping

Figure 9-1 Photovoltaic-powered fountains enhance

the CEME, U.K.

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.

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.

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).

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

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)

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

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.

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

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.

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

. Variable resistance

. Graph paper and pencil

. 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

. Computer with spreadsheet package

You will need

. Light source

. Three photovoltaic cells

. Voltmeter

. Ammeter

. Variable resistance

. Graph paper and pencil

. 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.

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”

. Variable resistance

. Graph paper and pencil

. 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.

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)

Project 26: Experimenting with Different Types

of Light Sources

Project 27: Experimenting with Direct

and Diffuse Radiation

. 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

. 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)

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.

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”

. 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

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.

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

. Nanocrystalline TiO2 Degussa P25 powder in

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

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

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)

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.

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:

. 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

You will need

. Ferrite rod antenna

. 60–160 pF variable capacitor

. BC183 transistor

. 10 nF capacitor

. 0.1 mF capacitor × 2

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

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.

. 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.

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

. 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

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

. 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.

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

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

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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

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.

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

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

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

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,

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

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)

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/

Toll-free: 1-800-494-1778

www.hobbytron.com/.html

Niagara Square

7555 Montrose Road

Niagara Falls ON, L2H 2E9

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

Orderline: 44-(0)-8457-201201

www.rswww.com

Maplin Electronics Ltd

National Distribution Centre

Valley Road

Wombwell, Barnsley

South Yorkshire S73 0BS

www.maplin.co.uk

Radio Shack

300 RadioShack Circle

Rapid Electronics Ltd

Severalls Lane

Colchester

Essex CO4 5JS

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

International Manufacturing Centre

University of Warwick

Coventry CV4 7AL

Inverters and power

regulators

Omnion Power Engineering

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

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

Tel: 44-(0)-1908-282111

Fax: 44-(0)-1908-282124

Photovoltaic modules

Advanced Photovoltaics Systems

BP Solar International

PO Box 191, Chertsey Road

Sunbury-on-Thames

Middlesex TW16 7XA

Tel: 44-(0)-1932-779543

Fax: 44-(0)-1932-762533

Siemens Solar Industries

52 East Magnolia Boulevard

Solar array structures, mounting

hardware

Kee Industrial Products Inc.

Toll-free: 1-800-851-5181

D-60388 Frankfurt/Main

Germany

Tel: 49-(0)-6109-5012-0

Fax: 49-(0)-6109-5012-20

vertrieb@keeklamp.com

Tel: 44-(0)-118-931-1022

Fax: 44(0)-118-931-1146

sales@keeklamp.com

Leveleg

8606 Commerce Ave

San Diego CA 92121-2654

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.

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

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

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

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

www.solarindustries.com/

Solar Twin Ltd

2nd Floor, 50 Watergate Street

Chester CH1 2LA

Tel: 44-(0)-1244- 403407

hi@solartwin.com

http://www.solartwin.com/pools.htm

Solar robotics supplies

N. America toll-free: 1-866-276-2687

Places to get more information

American BioEnergy Association

314 Massachusetts Avenue, NE

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

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

Energy Efficiency and Renewable Energy

Tel: 1-800-DOE-EREC or 1-800-363-3732

Fax: 1-703-893-0400

Doe.erec@nciinc.com

Florida Solar Energy Center (FSEC)

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

North Carolina Solar Center

Box 7401

North Carolina State University

Raleigh NC 27695-7401

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

Sandia National Laboratory—New Mexico

Solar Electric Light Fund

1612K Street NW, Suite 402

Washington DC 20006

USA

194 Supplier’s Index

Solar Energy Industries Association

www.seia.org/Default.htm

Solar Energy International

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

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