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By Vidhan Rana

Geothermal power is an inexhaustible supply of energy that is estimated to be equivalent to 42 million MW globally and can last for billions of years. Heat from the earth’s core is a significant source of energy and if developed properly, can fulfill a large proportion of our energy needs. In countries like Philippines and Iceland, geothermal accounts for over 15% of energy needs. In Iceland, geothermal energy provides over 90% of space- and water-heating needs. In the United States, however, less than 1% of our energy comes from geothermal. Geothermal Energy Association, a trade association for this industry, believes that geothermal can supply over 10% of our energy needs.

Unlike other renewable energy sources, geothermal power is available 24 hours a day and has a fairly constant rate of power generation. It essentially has no greenhouse gas emission and thus can serve a substitute for non –renewable sources of energy.

Geothermal energy can be harnessed in one of these three ways:

Electric Power Generation – where wells are drilled into a geothermal reservoir. Heat below the earth’s surface then boils the liquid, usually water, into vapor, which then drives the turbines that generate electricity. This is the most common form of geothermal power, but requires temperatures over 100 degrees Celsius (212 F). Therefore, only some regions in the country are able to generate electricity through this technique (Check map below for areas with geothermal potential).

Direct Use – heat from the earth is directly used, without involving heat pumps or a power plant, for space heating, food preparation, hot spring bathing and spas, agriculture, aquaculture, green houses and other industrial purposes. According to Oregon Institute of Technology’s Geo-Heat Center, U.S. installed capacity of direct use systems totals 470 MW or enough to heat 40,000 average-sized houses. In some cities, direct heat is used to melt snow on pavements and roads. A large part of Western and Central states in the U.S. has potential to utilize this source of energy.

Geothermal Heat Pumps – this system takes advantage of Earth’s relatively constant temperature at depths of about 10 ft to 300 ft. A geothermal heat pump system consists of pipes buried in the shallow ground near a building, a heat exchange, and ducts into the building. The pumps circulate water or other heat transfer fluids through pipes buried in a continuous loop, either horizontally or vertically, under a landscape area, parking lot, or any number of areas around the building. To supply heat, the system pulls heat from the Earth through the loop and distributes it through a conventional duct system. For cooling, the process is reversed; the system extracts heat from a building and transfers it below the earth’s surface. Though electricity is used to move the liquid around the system, heat pumps are estimated to be 30-60% more efficient than conventional heating and cooling systems. Because temperature at 10 ft under the surface ranges constantly between 10 and 16 degrees Celsius (50 and 60 degrees F), any area in the U.S. is suitable for this type of use.

The map below shows areas where geothermal resources are concentrated in the United States.

As the map above shows, geothermal resources are concentrated around the Western states. Therefore, these states have been in the forefront of geothermal energy generation. As of August 2008, a total of almost 3,000 MW of geothermal electricity power capacity was online in the U.S. About 2,500 MW of that capacity is currently installed in California.

California’s geothermal power generation exceeds the capacity of any other country in the world. The state derives around 4.5% of its energy needs from geothermal power plants. In addition to the installed capacity, a total of around 97 projects are under development in 13 different states with a total of 4,000 MW of new geothermal power plant capacity. In addition to the states that already have installed geothermal power generation capacity, states like Arizona, Colorado, Florida, Oregon, Washington and Wyoming are joining the geothermal market. California has another 930-1040 MW under development, while Nevada has another 1080-1900 MW under development. According to some estimates, geothermal power plants could be generating over 15,000 MW by 2025, more than quadrupling our current geothermal electricity generation.