Here's what will be put 'into' the 200 ft wells. Black polyethylene pipe loops will be pushed down into each well. Pipes will eventually be filled with a propylene-glycol/water solution. The liquid solution will absorb and maintain the temperature at that depth, which will be ~ 58 deg F. The ability to operate at a constant temp is the real selling feature of a geothermal system. A polymer grout will also be used to fill the well around the black pipe. The grout does a few important things for the well hole; it forms a thermal layer that aids in the transfer of heat, and also provides a low-permeability seal that bonds to the loops and the borehole wall... pretty cool stuff huh!
It is however very similar to the stuff that BP used at the bottom of the Gulf of Mexico to hold the oil drills in place. Hope ours works better than theirs did !
