Some facts about the USA and Geothermal Power Plants and Electricity Production

Geothermal energy provides more than 2700 megawatts (MW) of electric power — comparable to 60 million barrels of oil per year, enough for 3.5 million homes. This is only a small fraction of the potential value of geothermal energy in the U.S.

Geothermal electricity is clean — no fossil fuels are burned. Geothermal electricity produced in the U.S. displaces the emission of 22 million tons of carbon dioxide a year.

Geothermal electricity is reliable — plants have average system availabilities of 95% or higher, compared to 60-70% for coal and nuclear plants.

Geothermal electricity is cost-effective — today's cost of geothermal electricity ranges from $0.05 to $0.08 per kilowatt-hour, and technology improvements are steadily lowering that range. Also, the average geothermal power plant requires only 400 square meters of land to produce a gigawatt of power over 30 years. Compare that with the enormous amount of land needed for coal and nuclear plants and all the open-pit and other mining required to fuel them.

Geothermal electricity is homegrown — it reduces the need to import oil, reduces the trade deficit, and adds jobs to the U.S. economy.

Three power plant technologies are being used to convert hydrothermal fluids to electricity. The type of conversion used depends on the state of the fluid (whether steam or water) and its temperature:

Dry Steam Power Plants:
Steam plants use hydrothermal fluids that are primarily steam. The steam goes directly to a turbine, which drives a generator that produces electricity. The steam eliminates the need to burn fossil fuels to run the turbine. (Also eliminating the need to transport and store fuels) The oldest type of geothermal power plant. It was first used at Lardarello in Italy in 1904, and is still very effective. Steam technology is used today at The Geysers in northern California, the world's largest single source of geothermal power. These plants emit only excess steam and very minor amounts of gases.

Flash Steam Power Plants:
Hydrothermal fluids above 400 degrees F (200 degrees C) can be used in flash plants to make electricity. Fluid is sprayed into a tank held at a much lower pressure than the fluid, causing some of the fluid to rapidly vaporize, or "flash," to steam. The steam then drives a turbine, which drives a generator. If any liquid remains in the tank, it can be flashed again in a second tank to extract even more energy. Only excess steam and trace gases are emitted.

Binary-Cycle Power Plants:
Most geothermal areas contain moderate-temperature water (below 400 degrees F). Energy is extracted from these fluids in binary-cycle power plants. Hot geothermal fluid and a secondary (hence, "binary") fluid with a much lower boiling point than water pass through a heat exchanger. Heat from the geothermal fluid causes the secondary fluid to flash to steam, which then drives the turbines. Because this is a closed-loop system, virtually nothing is emitted to the atmosphere. Moderate-temperature water is by far the more common geothermal resource, and most geothermal power plants in the future will be binary-cycle plants.

The Future of Geothermal Electricity

Steam and hot water reservoirs are just a small part of the geothermal resource. The Earth's magma and hot dry rock will provide cheap, clean, and almost unlimited energy as soon as the technology to use them is developed. In the meantime, because they're so abundant, moderate-temperature sites running binary-cycle power plants will be the most common electricity producers.

Before geothermal electricity can be considered a key element of the U.S. energy infrastructure, it must become cost-competitive with traditional forms of energy. The U.S. Department of Energy is working with the geothermal industry to achieve $0.03 per kilowatt-hour. It is believed that the result will be about 15,000 megawatts of new capacity within the next decade.

The U.S. Department of Energy sponsors millions of dollars in research and development at national laboratories and universities. Investigators are working on issues in exploration, geochemistry, drilling, resource usage, and equipment operation.

The hot dry rock system once perfected could be used anywhere in the world. The system would be a closed system with the water captured after passing through the turbine blades injected back down to the reservoir to be converted into superheated steam.