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Unlike most of the other sources of renewable energy, geothermal energy does not derive directly or indirectly from the sun. The ultimate source of the earth's internal heat (estimated at six thousand degrees Celsius at the core) is still under debate, but the most likely explanation at this point is latent radioactive decay within the earth itself. Like hydrological power, geothermal energy production has its roots in our distant past; ancient Romans and Chinese frequently described the use of hot springs for medicinal or recreational purposes. In seismically active areas, such as Iceland, steam and heat from geysers has long been used as a source of energy. Current geothermal applications use water that has been heated beneath the earth's surface, as well as heat from the ground itself, and account for more renewable energy than any source except hydroelectric and biomass.

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There are several methodologies currently used to harness geothermal energy. The first is known as direct-source, and refers to using this latent energy directly. This is the method used by the ancients and modern resorts, such as those in Bath, England or Hot Springs, Arkansas. High temperature ground-water is pumped directly into radiators or water pipes, and is used to heat baths, saunas, or even industrial complexes. Of course, this requires an easily accessible high-temperature water source, and is therefore suitable only for certain geographical regions.

A ground source heat pump (a device used to transport heat from one location to another) is a potentially more wide-spread application of geothermal power. The idea of using a heat pump to draw energy from the ground was first suggested in 1912, and successfully demonstrated in the 1940s. A heat pump installed in a home or business can be used to heat during the winter, and as a heat sink to cool in the summer. They are relatively easy to install , and can be used almost anywhere. Some estimates suggest that over forty thousand heat pumps are installed annually world-wide.

A third use is geothermal electrical generation plants. In particular, steam from a geyser or other underground source is used to turn a turbine, in much the same way a a traditional fossil-fueled power generation plant operates, but without the use of incineration. Alternatively, a hole is drilled down to an area of “hot rocks,” and cold water is pumped in. Steam is created when the cold water hits the rocks, and that steam is used for the turbines. Unlike ground source heat pumps, geothermal electrical generation plants need to be built near the fault lines of tectonic plates or seismically active areas to have access to sufficient energy reserves, meaning that some of the best sites may be uncomfortably close to volcanoes or other magma flows.

There has been some evidence that drilling near fault lines can trigger seismic activity, such as earthquakes. Some potential plants have even been forced to abandon construction due to unstable tectonics. There is also an increase in the release of greenhouse gases from drilling into air pockets, though considerably less than from burning fossil fuels. Additionally, some long-term electrical plants, such as in California and New Zealand, have shown a decrease in productive capacity since their implementation. This is most likely due to water being removed from the natural system faster than it is replaced. Recent tests have shown that if water is re-injected into the system, full capacity can be restored.

In the United States, geothermal generators currently produce roughly the same amount of power as four nuclear power plants. A collection of geothermal plants in California known as “The Geysers” has been producing economically viable geothermal electricity since 1960s. Geothermal electrical generation exceeded fifteen percent of national power requirements in five countries: El Salvador, Kenya, Iceland, Philippines, and Costa Rica, yet his represents a small fraction of the potential geothermal energy. Unlike dams or wind farms, geothermal plants require very little land space, lessening their environmental impacts.

Published by Carol Foss - in the hope that it will make a difference, however small.