Geothermal Energy 

Erin Heidtke
Part of Iraq & Our Energy Future, by students of
Geography 378 (International Environmental Problems & Policy)
at the University of Wisconsin-Eau Claire, USA, Spring 2003.


    Geothermal energy is a renewable and sustainable power source that comes from the heat generated by the earth. "Geo" means earth and "thermal" means heat. The Earth has four main layers, as is shown in the first picture below (Geothermal Education Office). Each layer has different compositions, functions and temperatures, as is illustrated in the second figure below (Geothermal Education office). The heat of the earth radiates outward and sometimes melts the mantle at temperatures of 300° F- 700°F. When the mantle becomes melted magma is created. Sometimes magma reaches the surface of the crust and is then called lava. The magma reaches the crust and heats nearby rocks and water. The heated water can reach the surface and form hot springs and geysers.

    Geothermal energy creates less environmental pollution, is renewable and sustainable, avoids importing energy resources, benefits remote areas, adds to energy source diversity, creates less waste disposal and has a long life span.

    Geothermal energy is produced by drilling a well into the ground where thermal activity is occuring. Once a well has been identified and a well head attached, the steam is separated from the water, the water is diverted through a turbine engine which turns a generator. Usually the water is injected back into the ground to resupply the geothermal source. The pictures below illustrate how the set-up of a geothermal site collecting energy looks like (EIA kids site) and (Geothermal Education Office).

    Locations of Geothermal Energy Use

    Geothermal energy is generally harnessed in areas of volcanic activity. The Pacific Ring is a prime spot for the harnessing of geothermal activity because it is an area where the tectonic processes are always taking place. The picture below shows the general location of the Ring of Fire (EIA kids site).

    The USGS defines tectonic processes as a series of actions and changes relating to, causing, or resulting from structural deformation of the earth's crust. [Adapted from American Heritage Dic. of the English Language, 4th ed.] This picture illustrates the term tectonic processes (Geothermal Education Office).

    Geothermal power plants are used all over the world, but can not be located just anywhere. They are located where tectonic plates collide and generate volcanic activity. The map below shows where plate boundaries are located and the following map illustrates the general location of geothermal power plants being used around the world.

    The table below shows MW of Geothermal Energy in different countries around the world. For more information on the countries below, click on the name. For further information on other geothermal plants throughout the world visit this website, Selected Geothermal Power Plants (ORMAT GreEnergy Power).

    Zunil, Guatemala 24 MW
    São Miguel, Açores Islands, Portugal 14 MW
    Leyte, The Philippines 125 MW
    Olkaria, Kenya 100 MW
    Nagqu, Tibet, P.R. of China 1.0 MW
    Reykjanes Peninsula, Iceland 9.1 MW

    The table below shows the countries that are using Geothermal Energy and the number of Megawatts that their power plants produce.

    Producing countries in 1999 Megawatts

    United States

    Philippines 1,848
    Italy 768.5
    Mexico 743
    Indonesia 589.5
    Japan 530
    New Zealand 345
    Costa Rica 120
    Iceland 140
    El Salvador 105
    Nicaragua 70
    Kenya 45
    China 32
    Turkey 21
    Russia 11
    Portugal (Azores) 11
    Guatemala 5
    French West Indies (Guadeloupe) 4
    Taiwan 3
    Thailand 0.3
    Zambia 0.2

    Within the United States, the West (and specifically California) are major producers of Geothermal Energy. Each state has different regulations on geothermal energy. According to the Bureau of Land Management in California, , "The Geothermal Steam Act of 1970, as amended, (84 Stat, 1566; 30 U.S.C. 1001-1025) provides the Secretary of the Interior with the authority to lease public lands and other federal lands, including National Forest lands, for geothermal exploration and development in an environmentally sound manner. This authority has been delegated to the Bureau of Land Management (BLM). BLM implements the Act through the regulations contained in 43 Code of Federal Regulations (CFR) Part 3200." The table below shows the amount of money, leases and megawatts produced in California during the Fiscal Year 2000 (October 1, 1999-September 30, 2000).

    Types of Geothermal Power Plants

    Geothermal technology has three varied ways of taking geothermal energy and turning it in to useable energy for humans to use. The most common systems are steam and binary power plants. There are two different types of steam power plants: dry steam and flash steam. The following definitions and pictures are from Geothermal Technologies Program or Godfrey Boyle in Renewable Energy: Power for a Sustainable Future.

    Dry Steam Power Plants or Hot Dry Rock Power Plants

  • Vapor dominated resources where steam production is not contaminated
  • Steam is 1050°F - 1220° F
  • Steam passes through turbine
  • Steam expands
  • Blades and shaft rotate and generate power
  • Cooling towers generate waste heat
  • Most common and most commercially attractive (Godfrey Boyle)
  • Used in areas where geysers do not exist
  • Need water to inject down into rock
  • Well is deep
  • Takes more time to inject water in well

    Binary cycle power plant

  • Uses lower-temperatures, but much more common, hot water resources (100° F 300° F).
  • Hot water is passed through a heat exchanger in conjunction with a secondary (hence, "binary plant") fluid with a lower boiling point (usually a hydrocarbon such as isobutane or isopentane).
  • Secondary fluid vaporizes, which turns the turbines, which drive the generators.
  • Remaining secondary fluid is simply recycled through the heat exchanger.
  • Geothermal fluid is condensed and returned to the reservoir.
  • Binary plants use a self-contained cycle, nothing is emitted.
  • Energy produced by binary plants currently costs about 5 to 8 cents per kWh.
  • Lower-temperature reservoirs are far more common, which makes binary plants more prevalent.
  • Flash or Steam plants

  • Use very hot (more than 300° F) steam and hot water resources (as found at The Geysers plants in northern California)
  • Steam either comes directly from the resource, or the very hot, high-pressure water is depressurized ("flashed") to produce steam.
  • Steam then turns turbines, which drive generators that generate electricity.
  • Only significant emission from these plants is steam (water vapor).
  • Minute amounts of carbon dioxide, nitric oxide, and sulfur are emitted, but almost 50 times less than at traditional, fossil-fuel power plants.
  • Energy produced this way currently costs about 4-6 cents per kWh.