Geothermal Energy Systems

Geothermal ("Earth-heat") energy comes from the residual heat left over from the Earth's formation and from the radioactive decay of atoms deep inside the Earth. This heat is brought up to the Earth's crust by molten rock (magma) and by conduction through solid rock. There it raises the temperature of the Earth's surface and of groundwater trapped in the fissures and pores of underground rock, forming zones called hydrothermal (hot water) reservoirs.

Diagram showing the geothermal water cycle. Rainwater seeps into the ground and is heated by hot subsurface rocks, forming reservoirs of hot water that can make its way back to the surface through fissures.

The geothermal water cycle.

Geothermal energy can currently be harnessed in three different ways:

  • Electricity production is possible with the best (hottest) hydrothermal resources.

  • Lower-temperature hydrothermal resources can be used directly for space and water heating.

  • Geothermal heat pumps (GHPs) can be used for space heating and cooling anywhere in the country.

Read the following for more information:

The following organizations provide information about several geothermal energy technologies:

  • DOE Geothermal Technologies Program

    Sponsors research to develop geothermal science and technology, and works closely with industry to help commercialize research discoveries. Publishes brochures and newsletters about geothermal energy and its applications.

  • Geothermal Resources Council

    National and international industry trade association. Promotes the development of all types of geothermal resources. Periodically schedules a basic introductory course on geothermal energy.

  • Geothermal Energy Association

    U.S. industry trade association. Promotes the development of all geothermal resources, and provides comprehensive information on geothermal power projects. GEA has published A Guide to Geothermal Energy and the Environment (PDF 1.1 MB) and An Assessment of Geothermal Resource Development Needs in the Western United States (PDF 2.4 MB). Download Adobe Reader.

  • Geo-Heat Center

    The primary source of data and information about all types of direct use applications. The Center provides technical assistance to companies and individuals planning direct use projects.

  • Geothermal Education Office

    Focuses on helping students learn about geothermal energy. Provides teachers and other interested parties with free booklets, statistical maps, and reference material. Other materials are available at cost.