As of 2019, worldwide geothermal power capacity amounts to 15.4 gigawatts (GW), of which 23.9% (3.68 GW) are installed in the United States.[4] International markets grew at an average annual rate of 5 percent over the three years to 2015, and global geothermal power capacity is expected to reach 14.5–17.6GW by 2020.[5] Based on current geologic knowledge and technology the Geothermal Energy Association (GEA) publicly discloses, the GEA estimates that only 6.9% of total global potential has been tapped so far, while the IPCC reported geothermal power potential to be in the range of 35GW to 2TW.[3] Countries generating more than 15 percent of their electricity from geothermal sources include El Salvador, Kenya, the Philippines, Iceland, New Zealand,[6] and Costa Rica. Indonesia has an estimated potential of 29GW of geothermal energy resources, the largest in the world; in 2017, its installed capacity was 1.8GW.
Geothermal power is considered to be a sustainable, renewable source of energy because the heat extraction is small compared with the Earth's heat content.[7] The greenhouse gas emissions of geothermal electric stations average 45grams of carbon dioxide per kilowatt-hour of electricity, or less than 5% of those of conventional coal-fired plants.[8]
As a source of renewable energy for both power and heating, geothermal has the potential to meet 3 to 5% of global demand by 2050. With economic incentives, it is estimated that by 2100 it will be possible to meet 10% of global demand with geothermal power.[6]
In the 20thcentury, demand for electricity led to the consideration of geothermal power as a generating source. Prince Piero Ginori Conti tested the first geothermal power generator on 4 July 1904 in Larderello, Italy. It successfully lit four light bulbs.[9] Later, in 1911, the world's first commercial geothermal power station was built there. Experimental generators were built in Beppu, Japan and the Geysers, California, in the 1920s, but Italy was the world's only industrial producer of geothermal electricity until 1958.
Trends in the top five geothermal electricity-generating countries, 1980–2012 (US EIA)Global geothermal electric capacity. Upper red line is installed capacity; lower green line is realized production.
In 1958, New Zealand became the second major industrial producer of geothermal electricity when its Wairakei station was commissioned. Wairakei was the first station to use flash steam technology.[11] Over the past 60 years, net fluid production has been in excess of 2.5km3. Subsidence at Wairakei-Tauhara has been an issue in a number of formal hearings related to environmental consents for expanded development of the system as a source of renewable energy.[6]
In 1960, Pacific Gas and Electric began operation of the first successful geothermal electric power station in the United States at The Geysers in California.[12] The original turbine lasted for more than 30years and produced 11MW net power.[13]
The binary cycle power station was first demonstrated in 1967 in the Soviet Union and later introduced to the United States in 1981,[12] following the 1970s energy crisis and significant changes in regulatory policies. This technology allows the use of much lower temperature resources than were previously recoverable. In 2006, a binary cycle station in Chena Hot Springs, Alaska, came on-line, producing electricity from a record low fluid temperature of 57°C (135°F).[14]
Geothermal electric stations have until recently been built exclusively where high-temperature geothermal resources are available near the surface. The development of binary cycle power plants and improvements in drilling and extraction technology may enable enhanced geothermal systems over a much greater geographical range.[15] Demonstration projects are operational in Landau-Pfalz, Germany, and Soultz-sous-Forêts, France, while an earlier effort in Basel, Switzerland was shut down after it triggered earthquakes. Other demonstration projects are under construction in Australia, the United Kingdom, and the United States of America.[16]
The thermal efficiency of geothermal electric stations is low, around 7–10%,[17] because geothermal fluids are at a low temperature compared with steam from boilers. By the laws of thermodynamics this low temperature limits the efficiency of heat engines in extracting useful energy during the generation of electricity. Exhaust heat is wasted, unless it can be used directly and locally, for example in greenhouses, timber mills, and district heating. The efficiency of the system does not affect operational costs as it would for a coal or other fossil fuel plant, but it does factor into the viability of the station. In order to produce more energy than the pumps consume, electricity generation requires high-temperature geothermal fields and specialized heat cycles.[citation needed] Because geothermal power does not rely on variable sources of energy, unlike, for example, wind or solar, its capacity factor can be quite large – up to 96% has been demonstrated.[18] However the global average capacity factor was 74.5% in 2008, according to the IPCC.[19]
Resources
Enhanced geothermal system 1:Reservoir 2:Pumphouse 3:Heatexchanger 4:Turbinehall 5:Productionwell 6:Injectionwell 7:Hot water to district heating 8:Poroussediments 9:Observationwell 10:Crystallinebedrock
The Earth's heat content is about 1×1019TJ (2.8×1015TWh).[3] This heat naturally flows to the surface by conduction at a rate of 44.2 TW[20] and is replenished by radioactive decay at a rate of 30TW.[7] These power rates are more than double humanity's current energy consumption from primary sources, but most of this power is too diffuse (approximately 0.1 W/m2 on average) to be recoverable. The Earth's crust effectively acts as a thick insulating blanket which must be pierced by fluid conduits (of magma, water or other) to release the heat underneath.
Electricity generation requires high-temperature resources that can only come from deep underground. The heat must be carried to the surface by fluid circulation, either through magma conduits, hot springs, hydrothermal circulation, oil wells, drilled water wells, or a combination of these. This circulation sometimes exists naturally where the crust is thin: magma conduits bring heat close to the surface, and hot springs bring the heat to the surface. If a hot spring is not available, a well must be drilled into a hot aquifer. Away from tectonic plate boundaries the geothermal gradient is 25–30°C per kilometre (km) of depth in most of the world, so wells would have to be several kilometres deep to permit electricity generation.[3] The quantity and quality of recoverable resources improves with drilling depth and proximity to tectonic plate boundaries.
In ground that is hot but dry, or where water pressure is inadequate, injected fluid can stimulate production. Developers bore two holes into a candidate site, and fracture the rock between them with explosives or high-pressure water. Then they pump water or liquefied carbon dioxide down one borehole, and it comes up the other borehole as a gas.[15] This approach is called hot dry rock geothermal energy in Europe, or enhanced geothermal systems in North America. Much greater potential may be available from this approach than from conventional tapping of natural aquifers.[15]
Estimates of the electricity generating potential of geothermal energy vary from 35 to 2000GW depending on the scale of investments.[3] This does not include non-electric heat recovered by co-generation, geothermal heat pumps and other direct use. A 2006 report by the Massachusetts Institute of Technology (MIT) that included the potential of enhanced geothermal systems estimated that investing US$1billion in research and development over 15years would allow the creation of 100GW of electrical generating capacity by 2050 in the United States alone.[15] The MIT report estimated that over 200×109TJ (200ZJ; 5.6×107TWh) would be extractable, with the potential to increase this to over 2,000ZJ with technology improvements – sufficient to provide all the world's present energy needs for several millennia.[15]
At present, geothermal wells are rarely more than 3km (1.9mi) deep.[3] Upper estimates of geothermal resources assume wells as deep as 10km (6.2mi). Drilling near this depth is now possible in the petroleum industry, although it is an expensive process. The deepest research well in the world, the Kola Superdeep Borehole (KSDB-3), is 12.261km (7.619mi) deep.[21] Wells drilled to depths greater than 4km (2.5mi) generally incur drilling costs in the tens of millions of dollars.[22] The technological challenges are to drill wide bores at low cost and to break larger volumes of rock.
Geothermal power is considered to be sustainable because the heat extraction is small compared to the Earth's heat content, but extraction must still be monitored to avoid local depletion.[7] Although geothermal sites are capable of providing heat for many decades, individual wells may cool down or run out of water. The three oldest sites, at Larderello, Wairakei, and the Geysers have all reduced production from their peaks. It is not clear whether these stations extracted energy faster than it was replenished from greater depths, or whether the aquifers supplying them are being depleted. If production is reduced, and water is reinjected, these wells could theoretically recover their full potential. Such mitigation strategies have already been implemented at some sites. The long-term sustainability of geothermal energy has been demonstrated at the Larderello field in Italy since 1913, at the Wairakei field in New Zealand since 1958,[23] and at the Geysers field in California since 1960.[24]
Power station types
Dry steam (left), flash steam (centre), and binary cycle (right) power stations.
Geothermal power stations are similar to other steam turbine thermal power stations in that heat from a fuel source (in geothermal's case, the Earth's core) is used to heat water or another working fluid. The working fluid is then used to turn a turbine of a generator, thereby producing electricity. The fluid is then cooled and returned to the heat source.
Dry steam power stations
Dry steam stations are the simplest and oldest design. There are few power stations of this type, because they require a resource that produces dry steam, but they are the most efficient, with the simplest facilities.[25] At these sites, there may be liquid water present in the reservoir, but only steam, not water, is produced to the surface.[25] Dry steam power directly uses geothermal steam of 150°C or greater to turn turbines.[3] As the turbine rotates it powers a generator that produces electricity and adds to the power field.[26] Then, the steam is emitted to a condenser, where it turns back into a liquid, which then cools the water.[27] After the water is cooled it flows down a pipe that conducts the condensate back into deep wells, where it can be reheated and produced again. At The Geysers in California, after the first 30 years of power production, the steam supply had depleted and generation was substantially reduced. To restore some of the former capacity, supplemental water injection was developed during the 1990s and 2000s, including utilization of effluent from nearby municipal sewage treatment facilities.[28]
Flash steam power stations
Flash steam stations pull deep, high-pressure hot water into lower-pressure tanks and use the resulting flashed steam to drive turbines. They require fluid temperatures of at least 180°C, usually more. This is the most common type of station in operation today.[citation needed] Flash steam plants use geothermal reservoirs of water with temperatures greater than 360°F (182°C). The hot water flows up through wells in the ground under its own pressure. As it flows upward, the pressure decreases and some of the hot water is transformed into steam. The steam is then separated from the water and used to power a turbine/generator. Any leftover water and condensed steam may be injected back into the reservoir, making this a potentially sustainable resource.[29][30]
Binary cycle power stations are the most recent development, and can accept fluid temperatures as low as 57°C.[14] The moderately hot geothermal water is passed by a secondary fluid with a much lower boiling point than water. This causes the secondary fluid to flash vaporize, which then drives the turbines. This is the most common type of geothermal electricity station being constructed today.[31] Both Organic Rankine and Kalina cycles are used. The thermal efficiency of this type of station is typically about 10–13%.[32] Binary cycle power plants have an average unit capacity of 6.3 MW, 30.4 MW at single-flash power plants, 37.4 MW at double-flash plants, and 45.4 MW at power plants working on superheated steam.[33]
This section needs to be updated. Please help update this article to reflect recent events or newly available information.(February 2021)
The International Renewable Energy Agency has reported that 14,438 megawatts (MW) of geothermal power was online worldwide at the end of 2020, generating 94,949 GWh of electricity. [35] In theory, the world's geothermal resources are sufficient to supply humans with energy. However, only a tiny fraction of the world's geothermal resources can at present be explored on a profitable basis.[36]
In 2021, the United States led the world in geothermal electricity production with 3,889 MW of installed capacity, a substantial increase from 2020 when it produced 2,587 MW. Indonesia follows the US as the second highest producer of geothermal power in the world, with 2,277 MW of capacity online in 2021.
Al Gore said in The Climate Project Asia Pacific Summit that Indonesia could become a super power country in electricity production from geothermal energy.[37] In 2013 the publicly owned electricity sector in India announced a plan to develop the country's first geothermal power facility in the landlocked state of Chhattisgarh.[38]
The geography of Japan is uniquely suited for geothermal power production. Japan has numerous hot springs that could provide fuel for geothermal power plants, but a massive investment in Japan's infrastructure would be necessary.[40]
Data are for the year 2021. Data are sourced from the EIA.[41] Only includes countries with more than 0.01 TWh of generation. Links for each location go to the relevant geothermal power page, when available.
Existing geothermal electric stations, that fall within the 50th percentile of all total life cycle emissions studies reviewed by the IPCC, produce on average 45kg of CO 2 equivalent emissions per megawatt-hour of generated electricity (kg CO 2eq/MW·h). For comparison, a coal-fired power plant emits 1,001kg of CO 2 equivalent per megawatt-hour when not coupled with carbon capture and storage (CCS).[8] As many geothermal projects are situated in volcanically active areas that naturally emit greenhouse gases, it is hypothesized that geothermal plants may actually decrease the rate of de-gassing by reducing the pressure on underground reservoirs.[43]
Stations that experience high levels of acids and volatile chemicals are usually equipped with emission-control systems to reduce the exhaust. Geothermal stations can also inject these gases back into the earth as a form of carbon capture and storage, such as in New Zealand[43] and in the CarbFix project in Iceland.
Other stations like the Kızıldere geothermal power plant, exhibit the capability to utilize geothermal fluids to process carbon dioxide gas into dry ice at two nearby plants resulting in very little environmental impact.[44]
In addition to dissolved gases, hot water from geothermal sources may hold in solution trace amounts of toxic chemicals, such as mercury, arsenic, boron, antimony, and salt.[45] These chemicals come out of solution as the water cools, and can cause environmental damage if released. The modern practice of injecting geothermal fluids back into the Earth to stimulate production has the side benefit of reducing this environmental risk.
Geothermal has minimal land and freshwater requirements. Geothermal stations use 404squaremeters perGW·h versus 3,632 and 1,335squaremeters for coal facilities and wind farms respectively.[46] They use 20litres of freshwater per MW·h versus over 1000litres perMW·h for nuclear, coal, or oil.[46]
Geothermal power stations can also disrupt the natural cycles of geysers. For example, the Beowawe, Nevada geysers, which were uncapped geothermal wells, stopped erupting due to the development of the dual-flash station.
Local climate cooling is possible as a result of the work of the geothermal circulation systems. However, according to an estimation given by Leningrad Mining Institute in 1980s, possible cool-down will be negligible compared to natural climate fluctuations.[48]
Geothermal power requires no fuel; it is therefore immune to fuel cost fluctuations. However, capital costs tend to be high. Drilling accounts for over half the costs, and exploration of deep resources entails significant risks. A typical well doublet in Nevada can support 4.5 megawatts (MW) of electricity generation and costs about $10 million to drill, with a 20% failure rate.[22] In total, electrical station construction and well drilling costs about 2–5million€ perMW of electrical capacity, while the levelised energy cost is 0.04–0.10€ perkW·h.[10] Enhanced geothermal systems tend to be on the high side of these ranges, with capital costs above $4million perMW and levelized costs above $0.054 perkW·h in 2007.[50]
Geothermal power is highly scalable: a small power station can supply a rural village, though initial capital costs can be high.[53]
The most developed geothermal field is the Geysers in California. In 2008, this field supported 15 stations, all owned by Calpine, with a total generating capacity of 725MW.[54]
Geothermal energy is thermal energy extracted from the Earth's crust. It combines energy from the formation of the planet and from radioactive decay. Geothermal energy has been exploited as a source of heat and/or electric power for millennia.
Geothermal heating is the direct use of geothermal energy for some heating applications. Humans have taken advantage of geothermal heat this way since the Paleolithic era. Approximately seventy countries made direct use of a total of 270 PJ of geothermal heating in 2004. As of 2007, 28 GW of geothermal heating capacity is installed around the world, satisfying 0.07% of global primary energy consumption. Thermal efficiency is high since no energy conversion is needed, but capacity factors tend to be low since the heat is mostly needed in the winter.
The potential for exploiting geothermal energy in the United Kingdom on a commercial basis was initially examined by the Department of Energy in the wake of the 1973 oil crisis. Several regions of the country were identified, but interest in developing them was lost as petroleum prices fell. Although the UK is not actively volcanic, a large heat resource is potentially available via shallow geothermal ground source heat pumps, shallow aquifers and deep saline aquifers in the mesozoic basins of the UK. Geothermal energy is plentiful beneath the UK, although it is not readily accessible currently except in specific locations.
Geothermal energy was first used for electric power production in the United States in 1960. The Geysers in Sonoma and Lake counties, California was developed into the largest geothermal steam electrical plant in the world, at 1,517 megawatts. Other geothermal steam fields operate in the western US and Alaska.
The Kawerau Power Station is a 100-megawatt geothermal power plant located just outside the town of Kawerau in the Bay of Plenty Region of New Zealand. The power station is situated within the Kawerau geothermal field, which is part of the Taupo Volcanic Zone. Completed in July 2008 by Mighty River Power at a cost of NZ$300 million, the plant's capacity proved greater than expected. The station is the largest single-generator geothermal plant in New Zealand.
The Geysers is the world's largest geothermal field, containing a complex of 18 geothermal power plants, drawing steam from more than 350 wells, located in the Mayacamas Mountains approximately 72 miles (116 km) north of San Francisco, California.
An enhanced geothermal system (EGS) generates geothermal electricity without natural convective hydrothermal resources. Traditionally, geothermal power systems operated only where naturally occurring heat, water, and rock permeability are sufficient to allow energy extraction. However, most geothermal energy within reach of conventional techniques is in dry and impermeable rock. EGS technologies expand the availability of geothermal resources through stimulation methods, such as 'hydraulic stimulation'.
Geothermal power in New Zealand is a small but significant part of the energy generation capacity of the country, providing approximately 17% of the country's electricity with installed capacity of over 900MW. New Zealand, like only a small number of other countries worldwide, has numerous geothermal sites that could be developed for exploitation, and also boasts some of the earliest large-scale use of geothermal energy in the world.
The Wairakei Power Station is a geothermal power station near the Wairakei Geothermal Field in New Zealand. Wairakei lies in the Taupō Volcanic Zone.
The Poihipi Power Station is a geothermal power station owned and operated by Contact Energy. It is located on Poihipi Road near Taupō in New Zealand.
Canada has substantial potential for geothermal energy development. To date, development has all been for heating applications. Canada has 103,523 direct use installations as of 2013. There is currently no electricity being generated from geothermal sources in Canada although substantial potential exists in the Canadian Cordillera. The most advanced project exists as a test geothermal-electrical site at the Mount Meager massif in British Columbia, where a 100 MegaWatt (MW) facility could be developed. Potential for enhanced geothermal energy systems (EGS) exists throughout Canada. There are six geothermal power and two direct use projects listed with the Canadian Geothermal Energy Association.
Geothermal power is very cost-effective in the Great Rift Valley of Kenya, East Africa. As of 2023, Kenya has 891.8 MW of installed geothermal capacity. Kenya was the first African country to build geothermal energy sources. The Kenya Electricity Generating Company, which is 74% state-owned, has built several plants to exploit the Olkaria geothermal resource; Olkaria I, Olkaria II, Olkaria IV, Olkaria V, and Wellhead generation plants, with a third private plant Olkaria III. Additionally, a pilot wellhead plant of 2.5 MW has been commissioned at Eburru and two small scale plants have been built by the Oserian Development Company to power their rose farm facilities with a total of 4 MW.
Geothermal energy is the second most used form of renewable energy in Russia but represents less than 1% of the total energy production. The first geothermal power plant in Russia, which was the first Binary cycle power station in the world, was built at Pauzhetka, Kamchatka, in 1966, with a capacity of 5 MW. The total geothermal installed capacity is 81.9 MW, with 50 MW coming from a plant at Verkhne-Mutnovsky.Two other plants were built on the Kamchatka Peninsula in 1999 and 2002. Two smaller additional plants were installed on the islands of Kunashir and Iturup in 2007. Most geothermal resources are currently used for heating settlements in the North Caucasus and Kamchatka. Half of the geothermal production is used to heat homes and industrial buildings, one third is used to heat greenhouses and 13% is used for industrial processes.
AltaRock Energy Inc. is a privately held corporation that focuses on the development of geothermal energy resources and enhanced geothermal systems (EGS). It is headquartered in Seattle, Washington and has a technology development office in Sausalito, California. AltaRock has filed patent applications and holds exclusive licenses for related intellectual property related to EGS. In 2008 it started its first project near The Geysers in California to demonstrate the ability of EGS to be a reliable, renewable and clean source for the production of electric power.
Japan has favorable sites for geothermal power because of its proximity to the Izu–Bonin–Mariana Arc. In 2007, Japan had 535.2 MW of installed electric generating capacity, about 5% of the world total. Geothermal power plays a minor role in the energy sector in the country: in 2013 it supplied 2596 GWh of electricity, representing about 0.25% of the country's total electricity supply.
Svartsengi power station is a geothermal power plant, which is located in the Svartsengi geothermal field, about 4 kilometres (2.5 mi) north of Grindavík, approximately 20 km (12 mi) SE of Keflavík International Airport and 45 km (28 mi) from Reykjavík. The electric power station was built in 1976 by HS Orka. It was the world's first combined geothermal power plant for electric power generation and hot water production for district heating.
The Olkaria Area is a region located immediately to the south of Lake Naivasha in the Great Rift Valley of Kenya, Africa. It is geothermally active and is being used to generate clean electric power. The region has an estimated potential of 2,000 MW. This is almost double the maximum daily electricity peak demand recorded in 2008/2009 for the entire country.
The Yangbajain Geothermal Field (羊八井地热田) is a geothermal field near the town of Yangbajain in Damxung County, Tibet Autonomous Region, China. The fluid is heated by magmatic activity not far below the surface. It is a tourist attraction and also supplies steam to a major power plant with 25 MW capacity.
The Puna Geothermal Venture (PGV) is a geothermal energy power plant on the island of Hawaii, the largest island in the state of Hawaii. The plant was shut down shortly after the start of the May 2018 lower Puna eruption, and resumed power generation in November 2020. The eruption had caused lava to flow over a PGV power substation, a warehouse and at least three geothermal wells that had been preventatively quenched and capped when lava fountains erupted nearby, eventually also cutting off road access.
Solar augmented geothermal energy (SAGE) is an advanced method of geothermal energy that creates a synthetic geothermal storage resource by heating a natural brine with solar energy and adding enough heat when the sun shines to generate power 24 hours a day. The earth is given enough energy in one hour to provide all electrical needs for a year. Available energy is not the issue, but energy storage is the problem and SAGE creates effective storage and electrical power delivery on demand. This technology is especially effective for geothermal wells that have demonstrated inconsistent heat or idle oil or gas fields that have demonstrated the proper geology and have an abundance of solar.
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