How Is Geothermal Power Used?
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Basics of Geothermal Power
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Geothermal power uses energy from the earth either to heat or cool houses directly, or to produce electricity. Water seeps down deep into the earth where it forms underground pools and even subterranean rivers. When hot molten rock, called magma, flows up from beneath the crust of the earth, it can come into contact with this water. This heats the water, turning it into steam, which can be used for geothermal power plants and heating systems. Heat pumps -- the third type of geothermal power -- work in a completely different way, relying on the temperature of the ground right below the surface of the earth.
Geothermal Power Plants
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All geothermal power plants use turbines driven by steam to generate power. The turbine is a giant bladed wheel like a propeller, and the pressure of the hot steam flowing through makes it turn. The turbine is attached to an electric generator, which turns its rotation into electricity. The simplest geothermal power plants are dry steam plants. In these plants, steam from a reservoir inside the Earth flows up through pipes to the turbine. Flash steam plants works slightly differently; hot, pressurized water is pumped up from the earth. When it reaches the turbine, the pressure is reduced and the water explosively expands or "flashes" into steam, creating a big burst of pressure to drive the turbine. The water is then cooled and piped back down into the earth where it is heated again. Binary steam plants, like flash steam plants, I pressurized hot water out. In a binary system, however, heat is transfered out of the piped water into a second loop of water, which it turns into steam to power the plant. The pressurized tube is then pumped back into the earth to carry more heat up.
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Geothermal Heating Systems
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Geothermal heating is usually found in places like Reykjavík, Iceland, which has an abundance of geothermal energy to exploit. Hot water is pumped out of the ground, but it is not used to drive a turbine. Instead, it is circulated through all the buildings in the district. The water runs through radiators, where some of its heat is leached out and used to warm the air in buildings. The cooled water is then pumped back down into the geothermal reservoir to gather more heat and start the cycle again. This process is often referred to as district heating.
Heat Pumps
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Although the temperature deep below the surface of the Earth can be extremely hot, a few feet below the surface of the earth it remains cool and mild - usually about 50 to 60°F. Geothermal heat pumps take advantage of this stability, pumping heat in and out of the earth to keep the air inside buildings at a steady temperature. During the summer, geothermal heat pumps transfer heat from inside a building into the earth, cooling things off indoors. When the temperature drops during the winter, the heat pumps do just the opposite, using the energy inside the earth to heat the house. In many areas, this is a much more efficient way to heat and cool building than conventional air-conditioners and heaters
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