Geothermal energy captures heat from rock and water below the earth's surface.
Geothermal energy can drive turbines that generate electricity using one of three technologies – dry steam, flash steam, or binary cycle. According to the U.S. Department of Energy’s Geothermal Technologies Program, the specific technology chosen for a site depends on the temperature of the geothermal resource and whether the resource is steam or liquid.
Geothermal energy is also used to directly heat or operate commercial buildings, industrial facilities, and residences. Here are five brief profiles of geothermal-powered facilities.
Operated by Calpine Corp., The Geysers is a 45-square mile complex in Northern California near San Francisco that includes 15 individual power plants. Permits to build two more plants at the site have been approved.
The first power plant at The Geysers went online in 1921 and provided enough electricity to run lights for the resort and spa that had been built there in 1852. But the plant didn’t prove competitive at the time with other power sources and the generator fell into disuse. The first commercial generator plant was developed there in 1955.
Now the complex, which is driven by dry steam from geothermal formations, generates about 725 megawatts of electricity and features innovations such as reclaimed water recharge. The capacity amounts to about 21 percent of California’s renewable energy production.
The U.S. Department of Defense established a goal of providing 25 percent of power for its installations from renewable sources by the year 2025. To that end, in 1978 the DOD established the Geothermal Program Office and appointed the U.S. Navy as the lead agency to manage geothermal exploration and development on Defense Department lands.
Under the Navy’s direction, geothermal energy projects have been established on military land in the West. California’s Mojave Desert is home to the Naval Air Weapons Station China Lake, which boasts 4 geothermal power plants using binary flash steam technology to produce 270 megawatt-hours. China Lake includes a geological formation known as the Coso volcanic field. The Navy worked with private investors to develop geothermal energy at this site, which went online in 1987.
Despite being so close to weapons ranges, the geothermal operation has been continually operational in producing electricity and has not interfered with defense operations. Revenue generated from the plant totally pays for the Navy’s Geothermal Program Office operations and supports other energy programs as well.
Another electric power station driven by volcanic geothermal energy is in the nation’s Aloha State. The station’s generators are powered by steam produced from heat of the legendary Kilauea Volcano.
Puna, in development since the 1960s, is Hawaii’s only commercial producer of geothermal-generated electricity. The current facility went online in 1993. It’s operated by Ormat Technologies, which acquired the plant in 2004.
The facility’s capacity is 30 megawatts, which is transmitted to the island’s grid and distributed to consumers by Hawaii Electric Light Company. Puna accounts for 20 percent of the island’s electricity needs and more than 30 percent of power generated from renewable resources in the state.
When geothermal energy from underground is coupled with a ground source heat pump, it can also be used to cool indoor spaces. Such a system has gone online at Ball State University.
Ball State drilled about 3,600 boreholes into the ground around the campus to create an earth connection subsystem, which is a network of pipes that circulate a fluid to absorb heat from the ground (for heating) or radiate heat into the surrounding soil (for cooling).
The university now uses that geothermal system coupled with ground source heat pumps to heat and cool 47 buildings with 5.5 million square feet of floor space. The university says the system is the largest of its kind in the nation.
The campus previously used four aging coal-fired boilers for heating. The university estimates that the new system will save $2 million annually and reduce the carbon footprint of the campus by half.
This resort, founded more than a century ago, is developed around a moderate-temperature geothermal resource that includes a surface spring. Before 2006, power for the resort 60 miles from Fairbanks was produced by diesel-powered generators.
The resort worked with United Technologies Corporation to develop a hybrid system that uses geothermal energy and reverse-engineered chiller components to produce the same 400kW of power at about 25 percent lower cost than that of the diesel generator.
Chena Hot Springs Resort generates electricity from geothermal resources and also uses geothermal energy to control the temperature in its greenhouses, the northernmost commercial year-round hydroponic operation in the nation. The greenhouses produce lettuce, tomatoes, herbs, small fruits, and zucchini, all of which are served in dishes at the resort’s restaurant.