A Definition of Geothermal Heat
What do The Geysers in the Mayacamas Mountains of San Francisco, the Coso Hot Springs in Inyo County, California, and Southern California's Imperial Valley have in common? Besides being notable tourist attractions, the areas are vast reservoirs of geothermal heat--heat that is produced and extracted from within the Earth. These reservoirs, and others, have the potential of meeting the global demand for heat and electricity by yielding a clean source of renewable energy.
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Basics
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The earth is made up of several distinct layers that range in depth, including the crust (outermost layer), mantle, outer core and inner core. The inner core is characterized by extremely high pressure and temperature. According to K. Saravanan in the book “Principles of Environmental Science and Technology,” the temperature of the Earth's core ranges between 18,032 degrees Fahrenheit and 21,632 degrees Fahrenheit, and its pressure is greater than 3 million times the pressure at sea level.
Geothermal heat is the excessive heat produced at the earth's core. It either finds its way to the crust by seeping through channels in the Earth's layers or is extracted by geothermal heat pumps.
Geothermal Heat Extraction
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Most of the world's geothermal heat energy is concentrated along the edges of its tectonic plates (where its volcanoes and seismic activity is maximum). Geothermal activity is highest in the “Ring of Fire”--an area that encircles the Pacific Ocean. It is bounded by South America, Central America, North America, the Philippines and Japan.
According to the U.S. Energy Information Administration, as of July 2010, the United States is the world leader in geothermal electricity production.
Geothermal power plants are concentrated in California, Nevada, Utah, Montana and Hawaii.
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Types of Geothermal Heat Resources
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According to Charles E. Brown in the book “World Energy Resources,” there are four main types of geothermal heat resources: magma systems, hot-dry rock, gropressured and hydrothermal.
Hydrothermal resources are classified into water- and steam-dominated systems. They are liquid- or steam-based systems, such as hot geysers, that are found close to hot magma near the surface of the earth. Most of the world's geothermal heat energy is hydrothermal in nature
Environmental Impact
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Geothermal heat is a renewable source of energy that causes negligible harmful environmental impact. Hydrogen sulfide gas is common in some hydrothermal resources, which is harmful in large concentrations. Geothermal power plants remove all noxious gases, including hydrogen sulfide, before purifying the extracted heat for end-use.
Applications of Geothermal Heat
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Geothermal heat is used for commercial drying of vegetables, lumber, ceramics and other products. Heat at temperatures exceeding 220 degrees Fahrenheit is used to produce electricity, which powers homes, offices and industries.
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References
- Photo Credit hotsprings and geysers image by Melissa Schalke from Fotolia.com
