Another albeit smaller form of geothermal energy is ground-sourced heat pumps to provide building heating and cooling. Basically you dig a well hole and circulate water in pipes running below ground where the temperature is moderate year round and use this as a heat sink/source for a heat pump using a refrigerant cycle to transfer heat to/from the building interior.

In summer the heat pump runs as an air conditioning system, but uses the below ambient temperature water to remove the heat from the compressed refrigerant instead of hot ambient air. In winter it runs in reverse, using the warmer than ambient temperature water to warm the evaporated refrigerant instead of struggling to pull heat out of cold ambient air.

The system does require electricity to power the compressor and the ground circulation pump and the initial capital cost for the additional equipment and drilling is much higher than a traditional AC and fossil fuel furnace/boiler, but the operating costs should be much lower.

I read about a homeowner building such a system here in New England (along with a windmill) and my congregation is planning such a system for our new building. Now if we could only find grants and gifts for building "green" like they have for solar and wind systems to pay for the extra upfront cost.

Another Rick