Geothermal Energy - the Power of Water
Geothermal energy provides more than 2700 megawatts (MW) of electric power to U.S. residents - 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.
Converting Steam and Hot Water to Electricity
Three power plant technologies are currently used to convert hydrothermal fluids to electricity – dry steam, binary cycle, and flash steam. The type of conversion used depends on the state of the fluid (whether steam or water) and its temperature.
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. It also eliminates the need to transport and store fuels! This is 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.
The Benefits of Geothermal Energy
The advantages of geothermal energy are many:
- It's clean - no fossil fuels are burned.
- It is produced in the U.S.
- It offsets the emission of as much as 22 million tons of carbon dioxide a year!
- It's reliable - plants have average system availabilities of 95% or higher, compared to 60-70% for coal and nuclear plants.
- It's 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.
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 for fueling them. Last but not least, geothermal electricity is homegrown - it reduces our need to import oil, reduces the trade deficit, and adds jobs to the U.S. economy.
The Future of Geothermal
Steam and hot water reservoirs are a fraction of the geothermal resource. The Earth's magma and hot dry rock will provide cheap, clean, and almost unlimited energy as soon as we develop the technology to use them. 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 more 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. We believe the result will be about 15,000 megawatts of new capacity within the next decade.