Solar-thermal and geothermal water-heating systems capture the sun or the earth's energy and use it to preheat extracted groundwater so that your water heater — whether it uses electricity, gas, or oil — has to raise the temperature only a small amount more to reach your desired tap temperature. Putting "free BTUs" to work with a solar-thermal or geothermal water-heating system means that volatile fuel prices affect only a small percentage of your total water-heating costs.

Alternative Energy