Geothermal power and conventional fossil fuel–powered technologies have similar power production cycles, and both generation types can be dispatched. Geothermal power’s primary advantage is its renewable fuel. Its primary disadvantage is that its fuel requires large investments over many years to characterize uncertain sources. Enhanced recovery techniques that use fracking may be the future of this renewable resource.
Underachiever. That’s what comes to mind when considering the state of geothermal power in the United States.
By all accounts, geothermal energy is a very attractive source of electric power. The heat of the earth is essentially endless, providing a sustainable source of energy—and power—far into the future. The technology is fairly well known. The U.S. has produced electricity from the stored energy in our planet’s crust since 1960. Furthermore, electricity from geothermal heat, unlike that from the wind or the sun, is dispatchable, and plants typically have capacity factors of 80% to 90%.
Today, geothermal power installations in the U.S. total 3,102 MW, according to the Geothermal Energy Association (GEA). Production is concentrated in nine states: Nevada, California, Utah, Idaho, Oregon, Alaska, Hawaii, New Mexico, and Wyoming. The largest single project is also the oldest: The Geysers, located in the Mayacamas Mountains north of San Francisco, which began commercially generating electricity for Pacific Gas & Electric Co. in 1960. Now owned by Calpine, the 15 units at The Geysers have a net generating capacity of 725 MW, down considerably from their 2,000-MW peak in the 1980s (Figure 1).
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| 1. Renewable treasure. Naturally occurring high-pressure steam reservoirs in the Mayacamas Mountains north of San Francisco have been harnessed to produce electricity. This group of plants, collectively known as The Geysers, constitute the largest geothermal complex in the world. The Geysers produce one-fifth of California’s renewable energy. Courtesy: National Renewable Energy Laboratory |
The U.S. has the largest fleet of geothermal power plants in the world, although they supply only a tiny portion of the nation’s electricity. The second-largest geothermal system is in the Philippines, with total generating capacity of about 1,900 MW, which provides 27% of that country’s electricity (Figure 2).
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| 2. Island power. Ormat’s organic Rankine cycle modules were used at the 125-MW Upper Mahiao Geothermal Plant, located on the island of Leyte, Philippines. The plant went into service in 1996. Courtesy: Ormat Technologies Inc. |
Unrealized Potential
A recent Electric Power Research Institute (EPRI) report on geothermal commented, “Over the long term, the potential for geothermal power production can hardly be overstated. The earth’s crust serves as an insulating blanket over an otherwise hot planet. At different depths, there is hot rock virtually everywhere, meaning that the thermal resource is as geographically dispersed as sunshine and is often available just a few hundred to a few thousand feet underground.”
The geothermal industry has also developed exciting new technologies. It has moved beyond conventional steam turbines driven by geysers of superhot water gushing from the ground, exemplified by The Geysers. Companies such as U.S. Geothermal and Ormat Technologies employ binary generation technology developed by the federal government in the 1970s and 1980s. These binary plants use lower-temperature hot geothermal water to vaporize an organic liquid with a boiling point lower than water’s. The vapor produced is then expanded through a turbine generator to produce electricity, much as in a conventional steam plant. The condensed geothermal brine is then reinjected into the geothermal reservoir. According to U.S. Geothermal, 12 operating binary geothermal projects in the western U.S. today generate 184 MW of electricity (Figure 3).
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| 3. One of a dozen. U.S. Geothermal’s Raft River geothermal project, in operation in southern Idaho since early 2008, is one of 12 operating binary plants in the western U.S. The approximately 10 MW produced by Raft River is sold to Idaho Power. The company is currently constructing a new 8.6-MW plant outside San Emidio, Nev. Courtesy: U.S. Geothermal |
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