Geothermal energy
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Geothermal energy can be used as an efficient heat source in small end-use applications such as greenhouses, but the consumers have to be located close to the source of heat.

Geothermal energy - heat from the earth (in most cases mineral water)- is an important energy source having environmental and economic advantages over fossil and nuclear energy sources.

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Heat from the earth can be used as an energy source in many ways, from large and complex power stations to small and relatively simple pumping systems. This heat energy, known as geothermal energy, can be found almost anywhere—as far away as remote deep wells in Indonesia and as close as the dirt in our backyards. Tapping geothermal energy is an affordable and sustainable solution to reducing our dependence on fossil fuels, and the global warming and public health risks that result from their use.
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How Goethermal energy is captured

Three different types of power plants - dry steam, flash, and binary - are used to generate electricity 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. 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.

Dry Steam Power Plants
A dry steam power plant uses dry steam, typically above 235°C (455°F), to directly power its turbines. Dry steam is steam that contains no water droplets. All of the molecules are in a gaseous, as opposed to liquid, state. Dry steam plants are used where there is plenty of steam available that is not mixed with water. This is the oldest type of geothermal power plant and is still in use today. Dry steam plants are the simplest and most economical of geothermal plants. However, they emit small amounts of excess steam and gases. The geothermal plants at The Geysers are dry steam plants.

Flash steam
Flash steam power plants use hot water above 182 °C (360 °F) from geothermal reservoirs. The high pressure underground keeps the water in the liquid state, although it is well above the boiling point of water at normal sea level atmospheric pressure. As the water is pumped from the reservoir to the power plant, the drop in pressure causes the water to convert, or "flash", into steam to power the turbine and or generators. Any water not flashed into steam is injected back into the reservoir for reuse. Flash steam plants, like dry steam plants, emit small amounts of gases and steam.
Flash steam plants are the most common type of geothermal power generation plants in operation today. An example of an area using the flash steam operation is the CalEnergy Navy I flash geothermal power plant at the Coso geothermal field.

Binary-cycle
The water used in binary-cycle power plants is cooler than that of flash steam plants, from 107 to 182 °C (225-360 °F). 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, because they use fluids with a lower boiling point than water, are able to utilize lower temperature reservoirs, which are much more common. Most geothermal power plants planned for construction are binary-cycle.

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Advantages

Geothermal energy offers a number of advantages over traditional fossil fuel based sources. From an environmental standpoint, the energy harnessed is clean and safe for the surrounding environment. It is also sustainable 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 plants wor k continually, day and night, making them. From an economic view, geothermal energy is extremely price competitive in some areas and reduces reliance on fossil fuels and their inherent price unpredictability. 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.
 
 
     

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