[Christ]

Anyone ever built one that uses the temp differential between the outside air and the relatively stable temps about 30" under ground?

I'm talking about a really big one that could function on temp differentials as little as 10* or so.

Another option would be, during the day, to focus solar rays on it using a fresnel lens to increase the temp difference, but MY personal idea here is to keep it operating day and night, summer and winter, powering a low-output generator.

Any ideas?