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Source of Geothermal Energy
There are two primary sources of geothermal energy: primordial heat and radioactive decay. Primordial heat refers back to the earth's creation billions of years ago. The earth was formed by colliding cosmic matter that turned into extremely hot, large space debris orbiting the sun. As the surface of this space debris cooled, it became habitable and thus the earth as we know it. However, the cooled crust acts as insulation for the molten metal and rock at its core. Radioactive decay refers to the radioactive cosmic matter that helped form the earth. As it slowly decays in the crust, it releases large quantities of heat energy. The energy from these two sources manifests itself as hot springs, geysers and volcanoes.
Uses
Much of the world's energy comes from the artificial production of heat used to turn water into steam. The steam is used to power large turbines that create electricity. However, unlike nuclear energy, natural gas or coal, the source used to heat water is 100 percent natural geothermal energy. Instead of burning high concentrations of toxic materials to heat water, geothermal energy uses what already naturally seeps through cracks in the earth's crust. Besides being used to create electricity, geothermal energy can be used to heat large hot spring pools and laundries, and as a heat source for agriculture. Using geothermal energy for these purposes is called "direct use" because the heat is used for an immediate purpose requiring no transformation.
Transformation into Electricity
Electricity is made from geothermal energy in two ways: flash geothermal and binary geothermal. Flash geothermal refers to the use of high temperature geothermal heat exceeding 180 degrees Celsius. High temperatures are required to heat pressurized water that is injected into the geothermal heat source that rises back to the surface as pressurized steam. The steam is used to turn a large turbine that produces electricity. The water vapor is then released into the atmosphere or recollected to turn into steam again. Binary geothermal refers to the use of lower temperature geothermal heat. Because this heat is too low to flash water, a second, working fluid that has a low boiling point is used. It works by sending water down to the thermal source to be heated, and then flash heats the working fluid. The working fluid produces enough steam to turn a turbine that creates electricity. Neither the water nor the working fluid is ever exposed to the environment, which creates two closed loop systems (hence the name binary geothermal).
Issues
Drilling into the earth's crust is dangerous and extremely expensive. Many countries such as the United States, Japan and Iceland are already taking advantage of geothermal energy. However, current technology developed to drill into high heat rock costs millions of dollars. In addition, drilling into the earth's crust can be risky. Geothermal energy exploits are controversial because they have drained some popular geysers and destroyed the beauty that was once there. For example, three quarters of New Zealand's geysers have been lost due to geothermal energy exploits. Another controversy is the idea of draining naturally occurring hot springs to take advantage of geothermal activity and replacing them with artificial hot spring pools.