As one digs or drills into the Earth’s crust, temperatures increase at an average rate of about 25 C per kilometer or 60 F per mile. This heat stems from the molten conditions in the deep Earth, where magma is derived from Earth’s formation 4.6 billion years ago.
In some areas, as you dig into the Earth’s crust, the temperature increases more rapidly than the global average—with volcanic areas of Italy and California registering as high as 300 C at 2 km depth. When water co-occurs at these depths, it is found as vapor, which can be used to drive steam turbines for electricity when it is brought to the surface. One power plant near Larderello, Italy supplies electricity to nearly 600,000 homes.
In other areas, super-heated water turns to steam when it is brought to the surface, also allowing steam turbines to generate electricity. At shallower depths, water is best used directly as hot water or in heat pumps to heat or cool buildings, including private homes. In Reykjavik, Iceland, nearly 90% of the homes are heated with geothermal water.
All these sources of energy may be part of our energy future, but the deep, hot sources are of particular interest. Capturing even 1% of the thermal energy at depths of 3.5 to 10 km could provide 1,000x the annual energy use of the United States.
You can be sure we’ll be hearing more about geothermal energy as the coming decades play out.
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Web Links
See Moore and Simmons in Science, May 24, 2013
Photo, taken on March 29, 2010, courtesy of ThinkGeoEnergy via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY.