About 3,000 megawatts of direct geothermal electric capacity – electricity generated using heat from inside the earth—are produced in the United States annually. Direct geothermal power plants use naturally occurring steam and hot water, which originate under the earth’s surface. All of the geothermal plants in the United States are in California, Hawaii, Nevada, and Utah. Direct geothermal power plants use steam to rotate a turbine, which powers an electric generator. Another growing use of direct geothermal energy is to heat buildings using hot water. More than 600 megawatts of direct geothermal heating capacity are installed today.

 

Indirect geothermal systems use heat pumps and heat-exchange loops to extract or store heat energy underground. The heat extracted comes indirectly from solar energy absorbed by the soil.