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Journey to the center of the earth (well...not quite) to explore more about one of the hottest energy resources around. Geothermal power takes advantage of the Earth’s core heat to produce useable energy. How will your energy mix use geothermal?

Geothermal energy is energy we capture from heat stored in the Earth.

Geothermal power is used in two main ways: (1) for heating and cooling (2) to generate electricity. Underground temperature determines which of the applications is used.

Heating and Cooling
At a certain depth, the underground temperature remains relatively constant. Using geothermal heat pumps, these stable temperatures (55-60° F) can be tapped, and used in heating and cooling applications. In heating mode, heat is extracted from the earth by the geothermal heat pump and distributed to the home or building—typically through a system of air ducts. Cooler air from the building is returned into the ground to be reheated. In cooling mode, the process is reversed.

Producing Electricity
In some regions, including the United States’ West Coast and the West Coast of South America, underground temperatures are much higher because magma or molten rock is much closer to the earth’s surface. These regions can use the extreme temperatures to actually generate electricity.

To produce electric power from geothermal resources, underground reservoirs of steam or hot water are tapped by wells, and this steam is used to rotate turbines that generate electricity. Typically, water is returned to the ground to recharge the reservoir and reheat, completing the renewable energy cycle.

In some areas, water is already in steam form when it’s extracted through the wells. The world’s largest geothermal area is called "The Geysers", an area north of Napa Valley, California. Steam wells fuel twenty-one separate electric plants in this region, pumping out a total of 1000 MW of electricity.

Electrical Generation
However geothermal is used, there are many benefits. Geothermal produces no emissions. The resource is naturally renewable. Using this resource can help reduce the demand for fossil fuels – the only outside energy source you would need for heating/cooling air is for energy to run the heat pumps.

The biggest limitations of using geothermal to generate electricity is related to geography and geology – there are relatively few places on earth that have magma close enough to the earth’s crust to create the conditions necessary for generating electricity in an economical way. These locations are in regions where there are young volcanoes, crustal shifts, and recent mountain building.

See a clickable map of geothermal hotspots at the Geothermal Education Office site.

Cost is another limitation. Like some other types of electrical generation, the costs of drilling the wells and building the plants can be very expensive. Once all that initial money is spent, the cost of producing geothermal electricity is quite competitive with other forms of electrical generation. A geothermal heating/cooling system is more expensive to install than other systems. Over time though, experts say the savings in heating and cooling costs more than pay for the system. People who live in extreme climates can see the return on their investment within three to five years.

Check it out!
The thermal energy in the uppermost six miles of the earth’s crust amounts to 50,000 times the energy of all the oil and gas resources in the world.

The first experimental generation of electricity from natural steam happened at Laderello, Italy, in 1904. In 1913, a 250 kW generating station started generating electricity. It is still producing electricity today.

The Science Geek at ABC News online answers questions about geothermal power.



  1. Electric Power Research Institute. (Online) HTTP://www.epri.com. June 2001.
  2. Geothermal Education Office. "Geothermal Facts."
    http://geothermal.marin.org/GEOpresentation/sld067.htm. June 2001.
  3. National Renewable Energy Laboratory (NREL). "Geothermal Energy." (Online) HTTP://www.nrel.gov/documents/geothermal_energy.html. June 2001.






Places Around the World that Use Geothermal Energy
Iceland’s capital city of Reykjavik (rayk-yah-vick) gets 90 % of its heat for homes and public buildings by directing hot water from the earth into a system of pipes under the streets.

Geothermal Iowa
Geothermal heating reduces noise, is a cleaner energy source, and is easier to maintain than the old system.

Web Links
Where in the world is geothermal energy being used? Find out.