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Geothermal Power Types of Geothermal Sources

Most modern power generation relies on steam. Coal, oil, gas and nuclear power plants all produce electricity by heating steam to high temperatures and pressures and using that steam to spin a turbine, which generates electricity. The only material difference is the heat source. Geothermal power goes directly to the source by harnessing natural sources of steam, utilizing the heat of Earth's core. Within this broad definition are several subcategories of geothermal sources.

Hot Springs
- Hot springs and geysers form when there is a large reserve of magma close to Earth's surface. The magma heats underground reservoirs of water. When they emerge as springs, they can be tremendously hot. Hot springs were the target of the earliest geothermal experiments in the early 20th century. They easily are accessible and relatively simple to harness. However, they tend to cool significantly during their journey to the surface, making hot springs a less efficient producer of energy than other sources.
Hot Aquifers
- Like a hot spring, a hot aquifer is heated by a magma reserve. Unlike a hot spring, an aquifer does not have a natural outlet to the surface. Instead, a hot aquifer is a region of rock and soil that is saturated with hot, high-pressure water. Tapping a hot aquifer requires deep drilling, since a water source close to the surface generally finds a natural outlet. This makes a hot aquifer more difficult and expensive to exploit, but it has the advantage of providing much hotter steam at a higher natural pressure. This greatly can increase the efficiency and production potential of a geothermal plant.
Hot Dry Rock
- In many geologically active regions, large magma pockets are located close to the surface, but there are no significant sources of water between the magma and the surface. This natural heat can be harnessed using an injection well. Two shafts are drilled into hot dry rock until they reach a temperature capable of flash-evaporating water. Water or liquid carbon dioxide is pumped down one of the shafts and emerges from the second shaft as high-pressure steam capable of powering a turbine.
Magma
- In theory, a shaft could be drilled to an active magma tube, which essentially is an underground pipe filled with flowing liquid rock. This would produce large amounts of "dry steam," vaporized minerals such as silica, which could be used to produce turbine electricity at very high levels of efficiency. While magma-powered geothermal plants have a promising amount of potential, as of 2010, no working plants have been built utilizing magma power.

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