Natural steam from the production wells power the turbine generator. The steam is condensed by evaporation in the cooling tower and pumped down an injection well to sustain production.
Slide 37 of 122, © 2000 Geothermal Education OfficeGeothermal power (from the Greek roots geo, meaning earth, and therme, meaning heat) is energy generated by heat stored in the earth, or the collection of absorbed heat derived from underground, 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 2008, geothermal power supplies less than 1% of the world's energy.
Geothermal energy methods Geothermal resources range from shallow ground to hot water and rock several miles below the Earth's surface, and even further down to the extremely hot molten rock called magma. Wells over a mile deep can be drilled into underground reservoirs to tap steam and very hot water that can be brought to the surface for use in a variety of applications.
Geothermal technologies include:
Geothermal heat pump: Almost everywhere, the upper 10 feet of Earth's surface maintains a nearly constant temperature between 50 and 60°F (10 and 16°C). A geothermal heat pump system consists of pipes buried in the shallow ground near the building, a heat exchanger, and ductwork into the building. In winter, heat from the relatively warmer ground goes through the heat exchanger into the house. In summer, hot air from the house is pulled through the heat exchanger into the relatively cooler ground. Heat removed during the summer can be used as no-cost energy to heat water.
Direct exchange geothermal heat pump: A heat pump without a heat exchanger, which circulates the working fluid through pipes in the ground.
Hot water near Earth's surface can be piped directly into facilities and used to heat buildings, grow plants in greenhouses, dehydrate onions and garlic, heat water for fish farming, and pasteurize milk. Some cities pipe the hot water under roads and sidewalks to melt snow. District heating applications use networks of piped hot water to heat buildings in whole communities.
Hot dry rock geothermal energy: Using deep wells into hot rock, a fluid is heated and used to generate power:
Dry steam plants, which directly use geothermal steam to turn turbines;
Flash steam plants, which pull deep, high-pressure hot water into lower-pressure tanks and use the resulting flashed steam to drive turbines; and
Binary-cycle plants, which pass moderately hot geothermal water by a secondary fluid with a much lower boiling point than water. This causes the secondary fluid to flash to vapor, which then drives the turbines.
Advantages
Krafla Geothermal Station in northeast IcelandGeothermal energy offers a number of advantages over traditional fossil fuel based sources, primarily that the heat source requires no purchase of fuel. From an environmental standpoint, emissions of undesirable substances are small. It is also nearly sustainable because the heat extraction is small compared to the size of the heat reservoir, which may also receive some heat replenishment from greater depths. 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
From an engineering perspective, the geothermal fluid is corrosive, and worse, is at a relatively low temperature (compared to steam from boilers), which by the laws of thermodynamics limits the efficiency of heat engines in extracting useful energy as in the generation of electricity. Much of the heat energy is lost, unless there is also a local use for low-temperature heat; greenhouses, timber mills, district heating, etc.
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 substances back into the earth, thereby reducing carbon emissions to less than 0.1% of those from fossil fuel power plants. Hot water from geothermal sources will contain trace amounts of dangerous elements such as mercury, arsenic, antimony, etc. which if disposed of into rivers can render their water unsafe to drink.
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. Along with biomass, geothermal energy is one of the only two renewable energy sources which requires careful management in order to avoid depletion. For example, the world's second-oldest geothermal generator at Wairakei has reduced production. If left alone, however, these places will recover some of their lost heat, as the 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 TWh (total) 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'.[10]
A 2006 report by 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 present 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 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 4001 meters generally incur drilling costs in the tens 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 considered high in potential for development are the People's Republic of China, Hungary, Mexico, Iceland, and New Zealand. A number of potential sites are being developed or evaluated in South Australia that are several kilometres in depth.
Favorable locations for EGS (eg in central Australia) may only require wells 4 km deep (see hot dry rock geothermal energy).
History of development
Geothermal steam and hot springs have been used for centuries for bathing and heating, but it was not 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.
Development around the world
Geothermal power is generated in over 20 countries around the world including the United States, Iceland, Italy, Germany, Turkey, France, The Netherlands, Lithuania, New Zealand, Mexico, El Salvador, Nicaragua, Costa Rica, Russia, the Philippines, Indonesia, the People's Republic of China, Japan and Saint Kitts and Nevis. Chevron Corporation is the world's largest producer of geothermal energy. 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 could be developed.
Africa
Geothermal power is very cost-effective in the Rift area of Africa. Kenya was the first African country to build geothermal energy sources. 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). 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. In Ethiopia there is another plant for geothermal power (in 2008 some experts from Iceland calculated that Ethiopia has at least 1000 MW of that energy). Hot spots have been found across the continent, especially in the Great Rift Valley.
Germany
Internal view of the ORC-power plant located in Neustadt-Glewe / Northern GermanyElectricity from geothermal sources is expected to grow in Germany mainly because a law that benefits the production of geothermal electricity and guarantees the feeding. Less than 0.4 percent of Germany's total primary energy supply came from geothermal sources in 2004. But after a renewable energy law that introduced a tariff scheme of EU €0.15 [US $0.23] per kilowatt-hour (kWh) for electricity produced from geothermal sources came into effect that year, a construction boom was sparked and the new power plants are now starting to come online. However the first German geothermal power plant had been build in 2003 in Neustadt-Glewe located in northern Germany. This plant was not just the first one operating with the ORC-technology Organic Rankine Cycle but also with the lowest temperature.
According to the International Geothermal Association (IGA), worldwide, the Philippines ranks second to the United States in producing geothermal energy. As of the end of 2003, the US has a capacity of 2020 megawatts of geothermal power, while the Philippines can generate 1930 megawatts. (Mexico is third with 953 MW according to IGA). Early statistics from the Institute for Green Resources and Environment stated that Philippine geothermal energy provides 16% of the country's electricity. By 2005, geothermal energy accounted for 17.5% of the country's electricity production. More recent statistics from the IGA show that combined energy from geothermal power plants in the islands of Luzon, Leyte, Negros and Mindanao account for approximately 27% of the country's electricity generation. Leyte is one of the islands in the Philippines where the first geothermal power plant started operations in July 1977.
Saint Kitts and Nevis
The island of Nevis, long known for its numerous hot springs, commenced drilling for the construction of a geothermal powerplant at Spring Hill, Nevis, in January 2008. When completed (estimated 2010), the plant will supply 50 megawatts of electricity, enough to fulfill all of Nevis' demand (approximately 10 megawatts), and also enough to export to neighboring Saint Kitts as well as other nearby islands via submarine electrical transmission cables. The project, being undertaken by West Indies Power, will make Saint Kitts and Nevis the first country in the Caribbean to utilize large-scale Geothermal energy, and, when complete, will make Saint Kitts and Nevis one of the least dependent nations in the world on fossil-fuels.
