High Temperature Geothermal Heating

Heat from the Earth, or geothermal heat energy can be accessed by drilling water or steam wells in a process similar to drilling for oil. Geothermal energy is an enormous, underused heat and power resource that is clean (emits little or no greenhouse gases), reliable (average system availability of 95%), and homegrown (making us less dependent on foreign oil). Geothermal resources range from shallow ground to hot water and rock several miles below the Earth's surface, and even farther down to the extremely hot molten rock called magma. Mile-or-more-deep wells can be drilled into underground reservoirs to tap steam and very hot water that can be brought to the surface for use in a variety of applications. In the U.S., most geothermal reservoirs are located in the western states, Alaska, and Hawaii.

There are more than 120 locations in the United States which make direct use of geothermal heating. Most geothermal reservoirs are located in the western states, Alaska, and Hawaii. In most cases the hot water is tapped near the earth's by drilling to the heat source.  However, there are some locations where the hot water comes directly to the surface and little drilling is necessary.

There are a wide variety of uses for the heat which is extracted. Sometimes the water is pumped directly into facilities and used to heat buildings.  Some cities pipe the hot water under roads and sidewalks to melt snow. District heating applications use networks of piped hot water to heat buildings in whole communities.

Geothermal heating is also used extensively in agriculture to grow plants in greenhouses.  It can be used to dehydrate crops such as onions and garlic.  There are about 40 greenhouse complexes in the U.S. that use geothermal.  The heat can also be used in aquaculture to raise marine life that requires warm water temperatures such as catfish, tilapia, shrimp and tropical fish. It has even been used to raise alligators.

If a city is fortunate enough to have reasonable access to a geothermal heat source then accessing this form of energy can be extremely cost efficient.  The Geo-Heat Center at the U.S. Department of Energy has studied different approaches to extracting the heat and has found that groundwater heat pump systems are the most cost efficient approach.