Geothermal Power

Geothermal power is the use of geothermal heat to generate electricity.   Geothermal power supplies 0.416% of the world's energy.   If heat recovered by ground source heat pumps is included, the non-electric generating capacity of geothermal energy is estimated at more than 100 GW (gigawatts of thermal power) and is used commercially in over 70 countries.   During 2005, contracts were placed for an additional 0.5 GW of capacity in the United States, while there were also plants under construction in 11 other countries.   Although geothermal sites are capable of providing heat for many decades, eventually specific locations may cool down.   It is likely that in these locations, the system was designed too large for the site, since there is only so much energy that can be stored and replenished in a given volume of earth.   Some interpret this as meaning a specific geothermal location can undergo depletion, and question whether geothermal energy is truly renewable, but if left alone, these places will recover some of their lost heat, as the mantle has vast heat reserves.   The government of Iceland states it should be stressed that the geothermal resource is not strictly renewable in the same sense as the hydro resource.   It estimates that Iceland's geothermal energy could provide 1700 MW for over 100 years, compared to the current production of 140 MW. ^{Wiki n.p.}

There are three different types of power plants: dry steam, flash, and binary, which are used to generate power from geothermal energy, depending on temperature, depth, and quality of the water and steam in the area.   In all cases the condensed steam and remaining geothermal fluid is injected back into the ground to pick up more heat. ^{Wiki n.p.}

A dry stream power plant uses hot steam, typically above 235°C (455°F), to directly power its turbines. This is the oldest type of power plant and is still in use today.   Flash steam power plants use hot water above 182°C (360°F) from geothermal reservoirs. As the water is pumped from the reservoir to the power plant, the drop in pressure causes the water to vaporize into steam to power the turbine.   Any water not flashed into steam is injected back into the reservoir for reuse.   Binary-cycle power plants is cooler than that of flash steam plants.   The hot fluid from geothermal reservoirs is passed through a heat exchanger which transfers heat to a separate pipe containing fluids with a much lower boiling point.   These fluids, usually iso-butane or iso-pentane, are vaporized to power the turbine.   The advantage to binary-cycle power plants is their lower cost and increased efficiency. These plants also do not emit any excess gas and are able to utilize lower temperature reservoirs, which are much more common.   Most geothermal power plants planned for construction are binary-cycle.   In some locations, the natural supply of water producing steam from the hot underground magma deposits has been exhausted and processed waste water is injected to replenish the supply. Most geothermal fields have more fluid recharge than heat, so re-injection can cool the resource, unless it is carefully managed. ^{Wiki n.p.}

Geothermal energy offers a number of advantages over traditional fossil fuel sources.   From an environmental standpoint, the energy harnessed is clean and safe for the surrounding environment.   It is also sustainable (but not renewable) because the hot water used in the geothermal process can be re-injected into the ground to produce more steam.   In addition, geothermal power plants are unaffected by changing weather conditions.   Geothermal power works continually, day and night, to provide baseload power.   From an economic view, geothermal energy is extremely price competitive in some areas and reduces reliance on fossil fuels and their inherent price unpredictability.   Given enough excess capacity, geothermal energy can also be sold to outside sources such as neighboring countries or private businesses that require energy.   It also offers a degree of scalability: a large geothermal plant can power entire cities while smaller power plants can supply more remote sites such as rural villages.   Unfortunately, geothermal power can be used only where natural thermal heat is available.   There are several environmental concerns behind geothermal energy.   Construction of the power plants can adversely affect land stability in the surrounding region.   For example, increased seismic activity can occur because of well drilling and land subsidence can become a problem as older wells begin to cool down.   Dry steam and flash steam power plants also emit low levels of carbon dioxide, nitric oxide, and sulfur, although at roughly 5% of the levels emitted by fossil fuel power plants. ^{Wiki n.p.}

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Prince Piero Ginori Conti tested the first geothermal power plant on 4 July 1904, at the Larderello dry steam field in Italy.

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