Geothermal energy is heat ("thermal") derived from the earth ("geo"). It is the thermal energy contained in the rock and fluids, that fill the fractures and pores in the rocks that form the earth's crust.
High and Moderate temperature geothermal resources can be used to generate electricity. Low temperature geothermal resources can be used for a wide range of direct uses, e.g. district and space heating, industrial processes, greenhouses, aquaculture and spas.
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Unlike coal fired and natural gas fired power generation plants, the state of the art geothermal binary cycle plant produces virtually no emissions. When compared to natural gas, a 100 MW geothermal power generator offsets 190,000 pounds of NoX and SoX (nitrogen dioxide and sulphur dioxide) per year. Additionally, it eliminates 780 million pounds of CO2 emissions. The reduction in emissions, when compared to coal fired plants, is even greater. The binary cycle technology was pioneered at Raft River, Idaho in the early 1980s.
All types of geothermal energy are renewable as long as the rate of heat extraction does not exceed the rate at which the thermal reservoir it depends upon is renewed by heat from the earth's magna. Geothermal reservoirs that tap the earth's heat for energy production typically have 30 to 50 year life as the plant's equipment wears out. Indeed the world's first geothermal power plant at Larderello, Italy was commissioned in 1913 and is still producing. The Geysers, California facility has been in production since the early 1960s.
Yes, in particular with binary plants since the water produced from the fracture system can be re-injected back into the fracture system and reheated by the source rock. Currently, Calpines, the owner of Geysers, is constructing a $163 million, 41-mile pipeline to move the effluent water from the City of Santa Rosa's sewage system for injection into the geothermal reservoir. The Raft River property of US Geothermal Inc. ("USGEO") will involve a binary system to save and re-inject water back into the fractures for reheating. The scheduled reservoir modelling will identify where to position injectors for the maximum benefit.
In 1999, geothermal energy provided 0.4 % of US electricity generation, 14.3 million Megawatts hours (MWhr), enough electricity to service 1,400,000 average households. US geothermal capacity was 2,850 MW located primarily in California and Nevada.
The development of geothermal power thorough the 1990s has been impeded by two factors: location and cost. In respect of location, most geothermal reservoirs are located in the Western States and specifically in areas which enjoyed excess electrical capacity. For example, Raft River in Idaho and the Newberry Caldera in Oregon are within the Bonneville Power Authority (BPA) system, which distributes hydropower from the Columbia River dams. Local electrical distributors like Idaho Power, and Pacific Power could service their clients by purchasing from the BPA the lowest cost electricity in the USA.
In respect of costs, prior to recent technological advances, the cost of developing geothermal reservoirs, building generators and operating them was between 6 cents and 8 cents per kilowatt hour (Kwh). The major sources of new electrical power generation in the 1990s and until recently was coal and natural gas. These sources were competitive in the 4 to 6 cent per Kwh range.
Four factors have contributed to the current focus on geothermal energy:
Technology has lead to greater efficiencies in geothermal power generation due to (a) improvements in submersible pumps, (b) improvements in turbine efficiency © 3-D reservoir modelling techniques. When the Department of Energy (DOE) tested one of the world's first binary power plant at Raft River in the early 1980s, the highest volume pump they could use was a 600 gallons per minute (gpm) line shaft unit. Today, submersible pumps are utilized that exceed 2,800 gpm with greater energy efficiency and less maintenance. New turbine technology, like the GE Rotoflow Expansion Turbine delivers 20% and greater output. Additionally, the application of 3-D reservoir models, using tracer elements to map the fracture system will ensure that development wells are located for maximum productivity. Preliminary engineering at Raft River indicates that by applying these new technologies, wells that produced 1.3 net MW are now capable of approximately 3.4 net MW.
Simply, the Western States in which the geothermal reservoirs are located have the greatest increase in population in the USA over the last decade. More households mean more electricity is consumed. For example, the combined population of Idaho, Washington and Oregon in 1960 was 5,289,000. This reference year is important because, with the exception of the Hungry Horse dam, in Northwest Montana, the Columbia River hydro-dams, which the Army Corps of Engineers had commenced in the early 1940s, had been completed. The US Census Bureau population estimate for the same three states on June 1, 2001 was 10,782,000. The projection for 2010 is 12,018,000. Additionally, the state of Utah, which borders the Raft River location, grew from 891,000 in 1960 to 2,270,000 in 2001 and is projected to have a population of 2,551,000 in the year 2010.
Green Power represents sources of power that are non-polluting. These sources include solar, wind, geothermal as well as run-of the-stream hydro. Currently, the Green Power movement is gaining momentum from three initiatives, (a) voluntary green power purchases where consumers pay a premium to their local utility to in-turn purchase green power, (b) state and federal government departments being mandated to purchase green power, © state legislated renewable energy portfolio standards (RPS) which set targets for utilities to ensure that a minimum percentage of their supply is from green power. Nevada has instituted a RPS, which requires a minimum 15% green power component by the year 2013 scaled from 5% in 2003. New Mexico has adopted a 10% RPS, and California adopted a 20% RPS. Arizona, Oregon and Idaho are also in various stages of discussion, adoption or implementation of a RPS.
The growth of electrical demand, in the Western States, has been met through the 1990s and early in this decade by the construction and commissioning of combined cycle natural gas powered generators. These facilities meet current federal emission requirements, can be constructed in a short timeframe, and if scaled in the 250 MW size and greater, they cost approximately $850,000 to $900,000 per MW of capacity. However, in comparison to geothermal and wind power, they have higher operating costs due to the purchase price of natural gas. The Energy Information Agency, in a report to Secretary Spencer Abraham, in December 2001 (entitled US Natural Gas Markets: Mid-Term Prospects For Natural Gas Supply), has determined that the reserve/life index of new gas reservoirs has fallen to 3.9 years. Additionally, in order to maintain deliverability at current levels, the rate of well drilling must be maintained. Accordingly, the wellhead price of natural gas must be high enough to generate new activity. Since mid-2000, wellhead prices have varied from $1.80 per MCF to over $9.00 per MCF. One-megawatt hour (MWhr) requires approximately 5.5 MCF of natural gas. The cost to deliver gas from the wellhead, depending upon your location in the USA, varies between $1.50 and $3.00 per MCF. Therefore delivered prices in the $5.00 to $6.00 range are not unusual. At $6.00 per MCF, the feedstock price is 3.3 cents per Kwh upon which you must add operating costs and recovery of capital. During the winter of 2001, delivered gas prices achieved $12.00 per MCF in California and the Pacific Northwest. Whereas well drilling activity for 2002 is 60% to 65% of 2001 activity, history is likely to be repeated. Geothermal energy has no feedstock cost.
During the Carter Administration of the late 1970s, the DOE was given a mandate to develop new non-petroleum sources of domestic energy. Raft River, Idaho was identified as a location for research because as early as the late 19th century local ranchers had discovered hot geothermal water while drilling irrigation wells. Additionally, the location is approximately 50 miles from the DOE's Idaho National Energy Laboratory, which administered the project.
The DOE from 1975 through 1983 expended over $40 million. In addition to drilling 5 producing wells, 2 injectors and a number of monitoring well they also developed the world's first binary power plant with a 7 MW capacity. The binary cycle technology was a major breakthrough since it proved that electricity could be generated from moderate temperature (100ºC to 300ºC) geothermal reservoirs. They also built a fish farm and a hothouse for growing orchids.
Binary power plants have a very high utilization rate. The US industry average over 98% operating efficiency. The binary fluid, isobutene, must be cooled down before it is recycled for vaporization in order to run the turbines. When the atmospheric temperature is high, power is used to run large fans in order to move the ambient heat from the binary fluid. Therefore the amount of deliverable electricity on a hot August day can be as much as 30% to 35% lower than in mid-February. Additionally, the well pumps and other mechanical systems in the plant consume electricity. New technology, referred as the Kalina cycle, has been developed to significantly reduce this differential.
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