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Background

Geothermal energy is the energy that can be harnessed using the heat that occurs naturally in the Earth. This heat can be found in volcanoes, hot springs, and geysers [1]. The high temperatures range from 225º F to 600º F [2] and occur in these areas due primarily to the decay of radio-active isotopes that occur within the rocks in the Earth's crust [3]. The surrounding ground water can then be heated, or water can be pumped into the hot areas to produce steam. This steam is what is captured to be used to create electricity through a turbine system.

Types and/or methods

There are three common types of geothermal power: dry steam, flash steam, and binary cycle. Dry steam uses the steam directly from the earth, flash steam pumps water into the hot areas to boil the water and create steam, and binary cycle uses a secondary fluid to power a generator[4].

Dry Steam

Power from dry stream geothermal plants is found directly from the Earth. The natural steam that is created from the geysers in the earth is channeled directly into a turbine that powers a generator. These systems are very rare; not many places on Earth contain enough natural energy in the the steam produced to provide sufficient power[5].

Dry Steam Geothermal (USGS).

The only dry stream power producer that is located in the United States is in California. In the Mayacamas Mountains, just north of San Francisco, The Geysers generates a net capacity of about 725 megawatts of electricity - enough to power 725,000 homes, or a city the size of San Francisco[6].

The Geysers in Northern California.

Flash Steam

Flash stream power is the most common type of geothermal power. This is because the hot water from the earth can be reused to produce more steam. The hot water is pumped up to the surface of the earth where its pressure is lessened and it is separated into steam and cool water. The steam is then collected and used for electricity, and the cooler water is pumped back down to the hot area to continue in the cycle.[7].

Flash steam (USGS).

Iceland's very first geothermal plant is a flash steam plant. The Bjarnarflag Geothermal Power Plant is located in North Iceland,and was built in 1969. Bjarnarflag takes the steam produced from the hot water in the ground to produce 3 megawatts of electricity. The water that is separated from the steam in this plant is used to heat the fresh water used for district heating in Bjarnarflag[8].

Flash steam system in Bjarnarflag, Iceland.

Binary Cycle

Power from the geothermal binary cycle is generated through the use of another liquid in a lower temperature (225º F-350º F). The water is pumped into the warm area. This hot water is then used to warm another liquid that contains a much lower boiling temperature. These two liquids never come into contact with each other, because once the second liquid is evaporated and the vapor is collected to turn the generator, the water continues on in the cycle[9].

Binary cycle (USGS).

A binary cycle geothermal plant is located in Wairakei, New Zealand. The Wairakei Geothermal Power Station was commissioned in 1958; it was the first of its kind in the world at the at time. Wairakei Geothermal Power Station is capable of generating 181 megawatts of electrical energy using the binary cycle, enough to power about 150,000 homes[10].

Wairakei Binary Cycle, New Zealand.

Utilized areas

There are multiple areas that are available for geothermal use in the world. Iceland currently generates 25% of its electricity from geothermal systems[11]. Geothermal energy is used to make up about 10% of New Zealand's electricity supply[12]. And in the United States there are plants located in Alaska, California, Hawaii, Idaho, Nevada, and Utah. In 2005, geothermal energy generated 25% of domestic electricity[13]. While many of the hot spots are being used resourcefully in the world, many seismically active areas are not.

Under-utilized areas

In order for geothermal power to be considered a possibility, the plant must be located in a part of the globe that is seismically active. This allows for a continuous source of heat where the water is being pumped. The active areas include: the Western United States, Iceland , New Zealand , the Philippines , and South America[14]. The United States has geothermal activity in Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming[15]. However, most of these resources are not being utilized.

Further reading

References

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