CHARACTERISTICS

Geothermal energy channels the heat and steam stored below the earth's surface to a turbine that then drives a generator to produce electricity. Underground heat sources such as hot water reservoirs can be tapped by drilling through the earth's layers. Some surface manifestations such as hot springs and geysers may also be tapped for electric generation. High-temperature steam sources are of the greatest value for generating electricity; geothermal plants operate over temperature ranges of 122-482ºF (50-250ºC), a relatively low heat compared to traditional fossil or nuclear plants.² As long as resources are sustainably managed, geothermal can serve a baseload power generating function with high availability. The rate at which the hot water or steam is replenished–either naturally or by injecting spent fluids–determines the quantity of energy that the source is capable of supplying on a continuous basis.

Geothermal energy produces minimal amounts of carbon dioxide and only traces of nitrogen oxide and sulfur dioxide emissions. Closed-loop systems, the newest generation of geothermal technologies, produce no airborne emissions. As a generator of baseload electricity, geothermal competes with fossil fuel power sources. Thus, every kW of electricity generated by a geothermal site avoids the emissions that would have otherwise been produced by combusting fossil fuels.

For power generation, geothermal is limited to site-specific availability, and locations may not be close to a transmission grid. However, there is tremendous untapped potential for developing geothermal resources in Asia, and new technologies under development will improve the economics of using smaller geothermal sites for power generation, increasing the number of sites with economic potential. Of the five forms of geothermal energy, only two–hydrothermal reservoirs and earth energy–are currently used for electric power generation. Technological advances must be made before the three other forms–geopressured brines, hot dry rock and magma–can be commercially developed.

SIZE:
1-110 MW

FEATURES:
Geothermal power plants are highly reliably and can operate 24 hours/day. Average availability is 80%, but many plants have >95% availability.

COST:
$840-2,500/kW

CURRENT USAGE:
6,300 MW installed in 21 countries worldwide. Direct use of geothermal water occurs in >40 countries.

POTENTIAL USAGE:
Additional 6,000 MW is potentially economic worldwide. Worldwide resource potential >40,000 MW.

ISSUES ASSOCIATED WITH IMPLEMENTING ACTION

• Availability of appropriate sites is limited and distributed unevenly.
• Production must be carefully managed if the resource is to remain sustainable.
• Initial capital and development costs are high; special materials and construction techniques are required to mitigate the erosion and corrosion caused by water and steam.
• Gases such as H₂S may be emitted from geothermal wells, but developers can collect and re-inject the gases.
• Cost per kWh is competitive with coal and nuclear power, but geothermal is not yet competitive with new NGCC technologies (where natural gas is readily available).

CLIMATE CHANGE IMPACT

EMISSION EFFECT:
    

CONDITIONS FOR EMISSIONS MITIGATION:

• Geothermal power plants meet the most stringent environmental regulations and release small amounts of CO₂. With advanced, closed-loop technologies (binary geothermal technology applied to resources with a temperature below 350ºF or 177ºC), no emissions are produced.

EMISSION ESTIMATE:
56 MtC/GWh avoided Newest generation of flash-steam plant emits only 1lb/CO₂/ MWh_e.

COST-EFFECTIVENESS:
Net cost is $0-144/ton of CO₂ avoided.

SECONDARY EFFECTS:
Sulfur emission rates range from zero to a small percentage of those produced by fossil fuels. Emits traces of nitrogen oxides. Produces some H₂S.

RESOURCES

• The U.S. Department of Energy is sponsoring several initiatives to develop geothermal technologies. These include:
  1. GT 4000, a market initiative, with a goal to have 4,000 MW of geothermal capacity on line in the U.S. by the year 2000, and 11,000 MW by 2010.
  2. GEOHEAT 1000 has the goal of displacing 1,000 MW of generating capacity with direct applications of low-grade geothermal energy, reducing emissions of greenhouse gases.
• Palmerini, C.G. 1993. Geothermal Energy, in Renewable Energy: Sources for Fuels
• Email discussion group and Question/Answer Service for geothermal-related questions: iga-group@geoscience.co.uk
• This site provides links to technical and market information for geothermal sources, and a report, titled "Geothermal Energy: Clean, Renewable Energy for the Benefit of Mankind and the Environment," http://solstice.crest.org/renewables/geothermal/grc/index.html
• Links to geothermal information sources and organizations can be found at: http://www.eren.doe.gov/geothermal/resource.html

CONTACTS

Geothermal Education Office
Tiburon, CA
Tel: (415) 435 4574
Fax: (415) 435 7737
geo@marin.org
http://geothermal.marin.org

Geothermal Energy Association
Washington, DC
Tel: (202) 383-2676
Fax: (202) 383-2678
http://www.geothermal.org

Geothermal Technology Organization
David, CA
Tel: (213) 977-7496
Fax: (213) 977-6333

International Geothermal Association
c/o IGA Secretariat, Institute of Geological and Nuclear Sciences
Wairakei Research Centre
Taupo, New Zealand
Tel: 64-7-374-8211
Fax: 64-7-374-8199
igasec@gns.cri.nz

U.S. Department of Energy
Allan Jelacic
Director, Geothermal Division
Tel: (202) 586-6054
Fax: (202) 586-8185
http://www.doe.gov