Chad you should PM Seldom Seen... He's got a somewhat vast amount of knowledge of such things, I wouldn't be surprised if he knew something worth knowing here. When I lived in the mountains, we had quite a few discussions about geothermal energy, for example.
I've often fantasized about doing this as well some day.. just put the bit opening to the south, with enough overhang to block the direct sun in the summer but let it in in the winter, and I it's a pretty efficient setup.
82 fj40, 99 uzj100, 06 gx470
05 525EXC, 01 XT225, 09 TTR125, 07 TTR90, 07 CRF50