Quick Facts
- California leads the Nation in electricity generation from nonhydroelectric renewable energy sources, including geothermal power, wind power, fuel wood, landfill gas, and solar power.
- Nevada has large geothermal resources and is second only to California in the generation of electricity from geothermal energy.
- The geologically active basin and range country in southern and eastern Oregon, as well as the Cascade Mountains in western Oregon, are promising sites for geothermal energy development.
- South Dakota has high geothermal and wind power potential.
- Utah is one of the few States with electricity generation from geothermal power sources.
Present & Future
Currently, around 1% of electricity generation in the United States comes from geothermal power. Energy content of domestic geothermal resources at a depth of about 2 miles is estimated to have as much energy that could equate to 30,000 year supply of energy at the current rate for the United States! Obviously the entire resource base is not recoverable, but a small percentage of this resource could make a huge difference to America’s energy portfolio. According to the Geothermal Energy Association, if the U.S. develops 5,635 MW of new geothermal power capacity it will result in 23,949 full-time jobs as well as create a 30 year economic output of almost $85 billion.
Sources: Department of Energy, Geothermal Energy Association
Background
Geothermal energy is derived from the Earth’s heat and has the ability to generate hot water, heating for buildings and electricity. It is accessed by drilling water or steam wells in a process similar to drilling for oil. Geothermal is a highly beneficial energy source because it is considered to be clean, reliable and domestically accessible.
Location & production
Geothermal energy sources are found in a range of areas, from the shallow ground to the hot water and rock located several miles beneath the Earth’s surface, and even deeper down into the Earth’s magma. Wells more than a mile long can be drilled into reservoirs located underground. Most geothermal reservoirs in the U.S. are found in the western states, Hawaii and Alaska.
Three different technologies are used to harness the energy from geothermal drilling in order to generate heating and electricity. These include geothermal heat pumps, direct-use applications and power plants.
Geothermal heat pumps, located in shallow ground near buildings, use heat from the Earth’s surface to heat and cool buildings. The pump consists of a series of pipes, a heat exchanger and duct work that leads into the building. During winter, heat from the ground passes through the exchanger and goes directly into the building. In contrast, during the summer, hot air from a building is pulled through the exchanger and back into the ground. The heat removed during that process can also be used to heat water at no cost during the summer. Geothermal heat pumps use significantly less energy than conventional heating systems and are more efficient when cooling buildings, which saves energy and money while reducing air pollution. These pumps could possibly replace the entire system of heating oil in homes, which currently uses 500,000 barrels of oil per day.
Like geothermal heat pumps, direct-use application systems use a series of pipes that pump hot water near the Earth’s surface directly into facilities and buildings. Geothermal hot water can be used for a range of functions, from heating buildings, raising greenhouse plants, drying crops and heating water at fish farms, to performing various industrial processes, such as pasteurizing milk. In some instances, cities pump hot water through pipes and under roads and sidewalks to melt snow.
While heat pumps and direct-use applications are primarily used to heat buildings and water, geothermal power plants are used to generate electricity. Wells are built very deeply into the earth to extract steam and hot water, which drive turbines. In turn, the turbines drive generators that produce electricity. Three different types of plants are currently being operated: dry steam plants, flash steam plants and binary-cycle plants. Dry steam plants use steam to directly move turbines, whereas flash steam plants pull high-pressure hot water into lower-pressure tanks to create flash steam and rotate turbines. The more commonly used binary-cycle plants pass geothermal hot water through a heat exchanger with a secondary fluid, which has a significantly lower boiling point than water. As a result, the secondary fluid vaporizes to turn the turbines, which then power the generators.
Sources: National Renewable Energy Laboratory (NREL) and U.S. Department of Energy (Energy Efficiency and Renewable Energy)