The word geothermal may conjure up images of hot springs and geysers, but the truth is that geothermal energy -heat from the earth-has the potential to be one of the cleanest, most efficient sources of renewable energy available on a worldwide basis. Because it comes from hot water and steam that already trapped beneath the earth's surface, geothermal energy can be extracted without burning coal, gas, or oil, and its production releases barely any carbon dioxide.
Source: Mariam Webster Dictionary Online
Geothermal plants are extremely efficient because the energy is available continuously, 24 hours a day 365 days a year. Geothermal power, essentially water and steam, can be used to heat homes and businesses as well as to generate electricity. And while wind and solar energy have a capacity factor of about 20-30 percent, geothermal capacity is more than 70 percent.
There are three types of geothermal power plants operating today:
- Dry steam plants, which pipe hot steam directly from geothermal reservoirs to spin turbines that generate electricity.
- Flash steam plants pull deep, very hot water up through a well into low-pressure tanks, turning some of it to steam to drive turbines. When the steam cools it condenses back into water and is returned to the ground.
- Binary cycle plants pass moderately hot geothermal water through a heat exchanger where the heat is transferred to another liquid, such as isobutene, with a lower boiling point than water. When this fluid is heated and turned to steam, it then drives the turbines.
Most geothermal plants in the US exist in western states, especially Alaska and Hawaii, as well as in Yellowstone National Park, where there are reservoirs of steam or hot water closer to the earth's surface. Geothermal energy can be tapped almost anywhere with geothermal heat pumps.
The city of Santa Rosa, California pipes the city's wastewater to The Geysers power plants nearby to be used as reinjection fluid, prolonging the life of the reservoir because it then recycles the treated wastewater. In the EU, geothermal plants are found in Iceland, Greece, Italy, Turkey, Germany, and Austria, and also as far away as the Wairakei field in New Zealand.
Reykjavik, Iceland heats 95 percent of its buildings using geothermal energy and is considered one of the cleanest cities in the worlds. Iceland has been expanding its geothermal power production to meet growing industrial and commercial energy demand. Geothermal energy currently supplies more than 10,000 MW to 24 countries and produces enough electricity to meet the needs of 60 million people.
One of the initial drawbacks to geothermal projects is their high start-up cost; a power plant requires approximately $0.05 per kWh, and wells can cost as much as $1 to $4 million each to drill. However costs are slowing dropping, and in 2006, a panel led by the Massachusetts Institute of Technology suggested that with federal support, geothermal power could play a major role in American's energy future.
The Geothermal Technologies Program expects to receive additional funds through the American Recovery and Reinvestment Act of 2009. Large-scale commercial production of geothermal power will take at least a decade of development and will require improvements on existing technology.