Because geothermal energy is generated by steam produced by underground hot-water reservoirs, its use has been limited to places where those geological features are easily accessible. Iceland, which has numerous hot springs, has become the world leader in geothermal energy; 89 percent of all indoor heating in the country comes from geothermal energy [source: International Geothermal Association]. The heating also is used widely in greenhouses to provide food year-round. In the United States, geothermal energy is primarily used in areas with the necessary geologic formations, such as the western states, Alaska and Hawaii [source: U.S. Department of Energy].
In general, building a geothermal power plant is more expensive than building one that runs on conventional fuel, so upfront cost concerns have also been a barrier to geothermal energy use. However, geothermal energy has gotten a boost from the growing interest in green energy sources, given that heat from the Earth's core is an endlessly renewable resource. Compared to other renewable energy sources, generating electricity from geothermal energy costs about as much as generating electricity from wind power; both are less expensive than the investment required for solar power [source: International Geothermal Association]. Because distribution is one of the largest costs associated with geothermal power, there is a significant cost savings if the plant is within a relatively close distance of where the heat or electricity will be used.
To make geothermal energy more widespread, researchers are exploring ways to take advantage of the Earth's natural heat even in areas where there are no hot springs or underground reservoirs. One method currently in development is known as an Enhanced Geothermal System (EGS). The technique involves drilling down to a hot layer of rock beneath the Earth's surface, then injecting cold water into the fractured pieces. The water, which is quickly heated after coming into contact with the rocks, is then directed into pipes that take it up to a geothermal power plant. The benefit of such a system is that it could be used almost anywhere. Another possibility, at some point in the future, would be to recover heat directly from the molten magma deep inside the Earth.
As promising as geothermal energy is as a clean energy, it's not widely used. This is partly because the plant has to locate where it can access the energy - like near a hot spring or geyser - and because the costs involved in accessing the underground resources and creating a geothermal power plant remain quite high. Some estimates put the start-up costs just to drill the well to access underground resources in the millions of dollars [source: REPP]. It also remains a technologically complex process to reach geothermal resources. As the technologies improve, both the cost and the means to access these geothermal resources will likely come down.
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