[Christ]

35x50 is about $3000 worth of block, about $1000 worth of mortar and sand... scale that up to 50x80 and we're up to around $7500 in materials, and that's just for 8" block and the 4 external walls. (Not counting windows/doors etc.)

So this particular piece of land has a stream which runs downhill from it, and still has a good stint downhill before the land levels off on the other side of the road... this is helpful in using a solar pre-heater, since I can place the pre-heater downhill slightly from the holding tank, which will allow thermal conduction to circulate the water.

A closed system might also be useful for Solar heating, provided I can get enough sunlight in winter time... it would only be a supplemental heating system, obviously, but to keep the floors warm and partially heat the house would work nicely. That system would use some alternative to anti-freeze though, and would have thermo-valves in it, as a "thermostatic control" to keep the fluid from heating the house beyond a given temp... when the valve closes, it sends the fluid into a bypass loop which allows it to cool (and probably create electricity via a fluid-driven motor connected to a generator.)