That was last April on PACCS.  I'll answer your question there, but pillars work well for direct loading.  You already saw mine.  Windows are good.  That's exactly my roof(s) if you run the decking the other direction (check with your steel supplier, I believe you have it wrong).  There are other issues that you should run by an engineer.  BTW, much of the conversation there is off-forum.  Feel free. 
 
I'd have to do some technical digging but I'm skeptical about dirt having adequate response time for electric generation.  There are higher temp dirt storage plans that apparently work, but you will always have the time factor.  Which is where liquids do better.  Currently awaiting a full PAHS thermal modelling which I expect will answer several long-standing questions.
 
Substantially raising insolation temp is simple, storing it isn't.  If you'd like technical papers, I have some.  References for more.  You're correct, earth heat storage works extremely well from my 14 yr perspective.