[stevehull]

This is where it is tough. Geothermal loop fields, in gravel, clay, or other easily dug soils are easy to do. Geothermal extraction in granite is tough - frankly almost impossible.

Three reasons for this:

The first is expense. Each ton of heat pump needs some 200 feet of a vertical column and drilling through granite is expensive.

Secondly, granite does not have the thermal conduction that wet soils have. The BTUs are there, but without good conduction to the pipe, then heat transfer is degraded. This is true even with bentonite slurry injected in well. Solid rock does not have the heat transfer that moist soils have.

Thirdly, because of number two, the vertical heat transfer pipes must be made longer that 200 vertical feet per ton - perhaps double. And for reason one, this gets even more expensive.

I ran into this in New Hampshire with a client (White Mountain area north of Conway). We had to add lots more solar collectors (water type), but we were fighting winter as that location, that far north has minimal sunshine in the winter.

Your location is FAR better for winter solar. My suggestion, to your otherwise excellent ideas, is to add lots more solar water panels for heat collection. Secondly, increase the size (volume) of the storage tank.

Steve