Geothermal Energy

Geothermal power (from the Greek words geo, meaning earth, and thermal, meaning heat) is energy generated by heat stored beneath the Earth's surface or the collection of absorbed heat in the atmosphere and oceans. Prince Piero Ginori Conti tested the first geothermal generator on 4 July 1904, at the Larderello dry steam field in Italy.The largest group of geothermal power plants in the world is located in The Geysers, a geothermal field in California. As of 2007, geothermal power supplies less than 1% of the world's energy.

The Nesjavellir Geothermal Power Plant in Iceland

Advantages

Geothermal energy offers a number of advantages over traditional fossil fuel based sources. From an environmental standpoint, the energy harnessed is clean and safe for the surrounding environment.It is also sustainable because the hot water used in the geothermal process can be re injected into the ground to produce more steam. In addition, geothermal power plants are unaffected by changing weather conditions.Geothermal power plants work continuously, day and night, making them base load power plants. From an economic view, geothermal energy is extremely price competitive in some areas and reduces reliance on fossil fuels and their inherent price unpredictability. It also offers a degree of scalability: a large geothermal plant can power entire cities while smaller power plants can supply more remote sites such as rural villages.

Disadvantages

There are several environmental concerns behind geothermal energy. Construction of the power plants can adversely affect land stability in the surrounding region. This is mainly a concern with Enhanced Geothermal Systems, where water is injected into hot dry rock where no water was before. Dry steam and flash steam power plants also emit low levels of carbon dioxide, nitric oxide, and sulfur, although at roughly 5% of the levels emitted by fossil fuel power plants.However, geothermal plants can be built with emissions-controlling systems that can inject these gases back into the earth, thereby reducing carbon emissions to less than 0.1% of those from fossil fuel power plants.

Although geothermal sites are capable of providing heat for many decades, eventually specific locations may cool down. It is likely that in these locations, the system was designed too large for the site, since there is only so much energy that can be stored and replenished in a given volume of earth. Some interpret this as meaning a specific geothermal location can undergo depletion, and question whether geothermal energy is truly renewable. If left alone, however, these places will recover some of their lost heat, as the earth's mantle has vast heat reserves. An assessment of the total potential for electricity production from the high-temperature geothermal fields in Iceland gives a value of about 1500 MWh or 15 TWh per year over a 100 year period. The electricity production capacity from geothermal fields is now only 1.3 TWh per year.

Potential

If heat recovered by ground source heat pumps is included, the non-electric generating capacity of geothermal energy is estimated at more than 100 GW (gigawatts of thermal power) and is used commercially in over 70 countries. During 2005, contracts were placed for an additional 0.5 GW of capacity in the United States, while there were also plants under construction in 11 other countries.

Estimates of exploitable worldwide geothermal energy resources vary considerably. According to a 1999 study, it was thought that this might amount to between 65 and 138 GW of electrical generation capacity using enhanced technology.

A 2006 report by the Massachusetts Institute of Technology (MIT), that took into account the use of Enhanced Geothermal Systems (EGS), concluded that it would be affordable to generate 100 GWe (gigawatts of electricity) or more by 2050 in the United States alone, for a maximum investment of 1 billion US dollars in research and development over 15 years.

The MIT report calculated the world's total EGS resources to be over 13,000 ZJ. Of these, over 200 ZJ would be extractable, with the potential to increase this to over 2,000 ZJ with technology improvements - sufficient to provide all the world's energy needs for several millennia.

The key characteristic of an EGS (also called a Hot Dry Rock system), is that it reaches at least 10 km down into hard rock. At a typical site two holes would be bored and the deep rock between them fractured. Water would be pumped down one and steam would come up the other. The MIT report estimated that there was enough energy in hard rocks 10 km below the United States to supply all the world's current needs for 30,000 years.

Drilling at this depth is now possible in the petroleum industry, albeit it is expensive. (Exxon announced an 11 km hole at the Chayvo field, Sakhalin. Lloyds List 1/5/07 p 6) Wells drilled to depths greater than 4000 metres generally incur drilling costs in the 10's of millions of dollars. The technological challenges are to drill wide bores at low cost and to break rock over larger volumes. Apart from the energy used to make the bores, the process releases no greenhouse gases.

Other important countries are China, Hungary, Mexico, Iceland, and New Zealand. There are a number of potential sites being developed or evaluated in South Australia that are several kilometres in depth.

History of development

Geothermal steam and hot springs have been used for centuries for bathing and heating, but it wasn't until the 20th century that geothermal power started being used to make electricity.

Prince Piero Ginori Conti tested the first geothermal power generator on 4 July 1904, at the Larderello dry steam field in Italy. It was a small generator that lit four light bulbs. Later, in 1911, the world's first geothermal power plant was built there. It was the world's only industrial producer of geothermal electricity until 1958, when New Zealand built a plant of its own.

The first Geothermal power plant in the United States was made in 1922 by John D. Grant at The Geysers Resort Hotel. After drilling for more steam, he was able to generate enough electricity to light the entire resort. Eventually the power plant fell into disuse, as it was not competitive with other methods of energy production.

In 1960, Pacific Gas and Electric began operation of the first successful geothermal power plant in the United States at The Geysers. The original turbine installed lasted for more than 30 years and produced 11 MW net power. The Geysers are currently owned by the Calpine corporation and the Northern California Power agency; and it currently produces over 750 MW of power.

The West Ford Flat power plant is one of 21 power plants at The Geysers

United States

The United States of America is the country with the greatest geothermal energy production.

The largest dry steam field in the world is The Geysers, 72 miles (116 km) north of San Francisco. The Geysers began in 1960, has 1360 MW of installed capacity and produces over 750 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 the City of Santa Clara's municipal Electric Utility (now called Silicon Valley Power). 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, California. 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 have a capacity of about 570 megawatts.

The Basin and Range geologic province in Nevada, southeastern Oregon, southwestern Idaho, Arizona and western 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.