ANother aspect that is grossly under-estimated is the thermal difference between surface temperatures (or rooftop) and the temperatures ten or twenty feet under the ground. I haven't dug into the numbers but I suspect there is enough difference between the two levels to drive a Carnot cycle engine, a Stirling engine, with enough power to actually support a household. Especially if you use solar concentrators in warm climates for the high band. Do any of the engineering types out there know what the DeltaT would have to be to produce a working equivalent of, say, 2000 square feet of PV paneling, which at present is about what an individual family would need to run entirely on PV?


A