Geothermal power

Geothermal power is the use of geothermal heat for electricity generation. It is often referred to as a form of renewable energy, but because the heat at any location can eventually be depleted it technically may not be strictly renewable. Geothermal comes from the Greek words geo, meaning earth, and therme, meaning heat. Geothermal literally means "earth heat".

Types of geothermal sources

Geothermal power is generated by mining the earth's heat. In areas with high temperature ground water at shallow depths, wells are drilled into natural fractures in basement rock or into permeable sedimentary rocks. Hot water or steam flows up through the wells either by pumping or through boiling (flashing) flow. Experiments are in progress to determine if a fourth method, deep wells into "hot dry rocks", can be economically used to heat water pumped down from the surface. A hot dry rock project in the United Kingdom was abandoned after it was pronounced economically unviable in 1989. HDR programs are currently being developed in Australia, France, Switzerland and Germany. Magma (molten rock) resources offer extremely high-temperature geothermal opportunities, but existing technology does not allow recovery of heat from these resources.

Electrical generation

Geothermal-generated electricity was first produced at Larderello, Italy, in 1904. Since then, the use of geothermal energy for electricity has grown worldwide to about 8,000 megawatts of which the United States produces 2,700 megawatts.

Three types of power plants are used to generate power from geothermal energy: Dry steam, flash, and binary. Dry steam plants take steam out of fractures in the ground and use it to directly drive a turbine that spins a generator. Flash plants take hot water, usually at temperatures over 200°C, out of the ground, and allows it to boil as to rises to the surface then separates the steam phase in steam/water separators and then runs the steam through a turbine. In binary plants, the hot water flows through heat exchangers, boiling an organic fluid that spins the turbine. The condensed steam and remaining geothermal fluid from all three types of plants are injected back into the hot rock to pick up more heat. This is why geothermal energy is viewed as sustainable. The heat of the earth is so vast that there is no way to remove more than a small fraction even if most of the world's energy needs came from geothermal.

The largest dry steam field in the world is The Geysers, about 90 miles (145 km) north of San Francisco began in 1960 which has 1360 MW of installed capacity and produces about 1000 MW net. Calpine Corporation now owns 19 of the 21 plants in The Geysers and is currently the United States' largest producer of renewable geothermal energy. The other two plants are owned jointly by the Northern California Power Agency and Santa Clara Electric. Since the activities of one geothermal plant affects those nearby, the consolidation plant ownership at The Geysers has been beneficial because the plants operate cooperatively instead of in their own short-term interest. The Geysers is now recharged by injecting treated sewage effluent from the City of Santa Rosa and the Lake County sewage treatment plant. This sewage effluent used to be dumped into rivers and streams and is now piped to the geothermal field where it replenishes the steam produced for power generation.

Another major geothermal area is located in south central California, on the southeast side of the Salton Sea, near the cities of Niland and Calipatria, CA. As of 2001, there were 15 geothermal plants producing electricity in the area. CalEnergy owns about half of them and the rest are owned by various companies. Combined the plants produce about 570 megawatts.

The Basin and Range geologic province in Nevada, southeastern Oregon, southwestern Idaho, Arizona and eastern Utah is now an area of rapid geothermal development. Several small power plants were built during the late 1980s during times of high power prices. Rising energy costs have spurred new development. Plants in Nevada at Steamboat near Reno, Brady/Desert Peak, Dixie Valley, Soda Lake, Stillwater and Beowawe now produce about 235 MW. New projects are under development across the state.

Geothermal power is very cost-effective in the Rift area of Africa. Kenya's KenGen has built two plants, Olkaria I (45 MW) and Olkaria II (65 MW), with a third private plant Olkaria III (48 MW) run by Israeli geothermal specialist Ormat. Plans are to increase production capacity by another 576 MW by 2017, covering 25% of Kenya's electricity needs, and correspondingly reducing dependency on imported oil.

Geothermal power is generated in over 20 countries around the world including Iceland (producing 17% of its electricity from geothermal sources), the United States, Italy, France, New Zealand, Mexico, Nicaragua, Costa Rica, Russia, the Philippines, Indonesia and Japan. Canada's government (which officially notes some 30,000 earth-heat installations for providing space heating to Canadian residential and commercial buildings) reports a test geothermal-electrical site in the Meager Mountain–Pebble Creek area of British Columbia, where a 100 MW facility might be developed at that site.

Desalination

Douglas Firestone began working with evaporation/condensation air loop desalination about 1998 and proved that geothermal waters could be used as process water to produce potable water in 2001. In 2003 Professor Ronald A. Newcomb, now at San Diego State University Center for Advanced Water Technologies began to work with Firestone to enhance the process of using geothermal energy for the purpose of desalination. Geothermal Energy is a primary energy source.

In 2005 testing was done in the fifth prototype of a device called the “Delta T” a closed air loop, atmospheric pressure, evaporation condensation loop geothermally powered desalination device. The device used filtered sea water from Scripps Institute of Oceanography and reduced the salt concentration from 35,000 ppm to 51 ppm w/w. Aqua Genesis Ltd - Delta T - Testing Information (accessed 30 March, 2006)

Water injection

In some locations, the natural supply of water producing steam from the hot underground magma deposits has been exhausted and processed waste water is injected to replenish the supply. Most geothermal fields have more fluid recharge than heat, so re-injection can cool the resource, unless it is carefully managed. In at least one location, this has resulted in small but frequent earthquakes (see external link below). This has led to disputes about whether the plant owners are liable for the damage the earthquakes cause.

Heat depletion

Although geothermal sites are capable of providing heat for many decades, eventually they are depleted as the ground cools. RESPONSE OF WAIRAKEI GEOTHERMAL RESERVOIR TO 40 YEARS OF PRODUCTION, 2006 (pdf) Allan Clotworthy, Proceedings World Geothermal Congress 2000. (accessed 30 March) The government of Iceland states It should be stressed that the geothermal resource is not strictly renewable in the same sense as the hydro resource. It estimates that Iceland's geothermal energy could provide 1700 MW for over 100 years, compared to the current production of 140 MW. However, the natural heat flow of the earth largely from radioactive decay does replenish the heat lost in geothermal heat mining.

Cost

Geothermal power is more competitive in countries that have limited hydrocarbon resources, such as Iceland, New Zealand, and Italy. During the period of low power prices in the 1980s to the recent rise in oil and gas prices, few geothermal resource areas in the United States were capable of generating electricity at a cost competitive with other energy sources. However, recent rises in power prices make geothermal more cost competitive.

Not all areas of the world have a usable geothermal resource, though many do. Also, some geothermal areas do not have a high enough temperature to produce steam. In those areas, geothermal power can be generated using a process called binary cycle technology, though the efficiency is lower. Other areas do not have the water to produce steam, which is necessary for current plant designs. Geothermal areas without steam are called hot dry rock areas and methods for exploiting them are being researched. Also, instead of producing electricity, lower temperature areas can provide space and process heating. As of 1998, the United States has 18 district heating systems, 28 fish farms, 12 industrial plants, 218 spas and 38 greenhouses that use geothermal heat.

References

External links

Geothermal Energy
Australian National University Hotrock website
Geodynamics - Australian Company developing Geothermal Electricity in Australia
US Department of Energy pages on geothermal energy
A University of Alaska article on geothermal energy
Geothermal Power News The latest geothermal news, updated daily

Alternative energy

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