Geothermal electricity 1

Geothermal electricityGeothermal electricity is electricity generated from geothermal energy. Technologies in use include dry steampower plants, flash steam power plants and binary cycle power plants. Geothermal electricity generation is currentlyused in 24 countries[1] while geothermal heating is in use in 70 countries.[2]

Estimates of the electricity generating potential of geothermal energy vary from 35 to 2000GW.[2] Currentworldwide installed capacity is 10,715 megawatts (MW), with the largest capacity in the United States (3,086MW),[3] Philippines, and Indonesia.Geothermal power is considered to be sustainable because the heat extraction is small compared to the Earth's heatcontent.[4] The emission intensity of existing geothermal electric plants is on average 122kg of CO2 permegawatt-hour (MWh) of electricity, a small fraction of that of conventional fossil fuel plants.[5]

History and development

Global geothermal electric capacity. Upper redline is installed capacity;[6] lower green line is

realized production.[2]

In the 20thcentury, demand for electricity led to the consideration ofgeothermal power as a generating source. Prince Piero Ginori Contitested the first geothermal power generator on 4 July 1904 inLarderello, Italy. It successfully lit four light bulbs.[7] Later, in 1911,the world's first commercial geothermal power plant was built there.Experimental generators were built in Beppu, Japan and the Geysers,California, in the 1920s, but Italy was the world's only industrialproducer of geothermal electricity until 1958.

In 1958, New Zealand became the second major industrial producer ofgeothermal electricity when its Wairakei station was commissioned.Wairakei was the first plant to use flash steam technology.[8]

In 1960, Pacific Gas and Electric began operation of the first successful geothermal electric power plant in theUnited States at The Geysers in California.[9] The original turbine lasted for more than 30years and produced11MW net power.[10]

The binary cycle power plant was first demonstrated in 1967 in Russia and later introduced to the USA in 1981.[9]

This technology allows the use of much lower temperature resources than were previously recoverable. In 2006, abinary cycle plant in Chena Hot Springs, Alaska, came on-line, producing electricity from a record low fluidtemperature of 57C.[11]

Geothermal electric plants have until recently been built exclusively where high temperature geothermal resourcesare available near the surface. The development of binary cycle power plants and improvements in drilling andextraction technology may enable enhanced geothermal systems over a much greater geographical range.[12]

Demonstration projects are operational in Landau-Pfalz, Germany, and Soultz-sous-Forts, France, while an earliereffort in Basel, Switzerland was shut down after it triggered earthquakes. Other demonstration projects are underconstruction in Australia, the United Kingdom, and the United States of America.[13]

The thermal efficiency of geothermal electric plants is low, around 10-23%,[14] because geothermal fluids are at a low temperature compared to 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 plant. In order to produce more energy than the pumps consume, electricity generation requires high temperature geothermal fields and specialized heat cycles. Because geothermal power does not rely on

Geothermal electricity 2

variable sources of energy, unlike, for example, wind or solar, its capacity factor can be quite large up to 96% hasbeen demonstrated.[15] The global average was 73% in 2005.

Resources

Enhanced geothermal system 1:Reservoir2:Pumphouse 3:Heatexchanger 4:Turbinehall

5:Productionwell 6:Injectionwell 7:Hot water todistrict heating 8:Poroussediments

9:Observationwell 10:Crystallinebedrock

The earths heat content is 1031joules.[2] This heat naturally flows tothe surface by conduction at a rate of 44.2 terawatts, (TW,)[16] and isreplenished by radioactive decay at a rate of 30 TW.[4] These powerrates are more than double humanitys current energy consumptionfrom primary sources, but most of this power is too diffuse(approximately 0.1 W/m2 on average) to be recoverable. The Earth'scrust effectively acts as a thick insulating blanket which must bepierced by fluid conduits (of magma, water or other) to release the heatunderneath.

Electricity generation requires high temperature resources that can onlycome from deep underground. The heat must be carried to the surfaceby fluid circulation, either through magma conduits, hot springs,hydrothermal circulation, oil wells, drilled water wells, or acombination of these. This circulation sometimes exists naturallywhere the crust is thin: magma conduits bring heat close to the surface,and hot springs bring the heat to the surface. If no hot spring isavailable, a well must be drilled into a hot aquifer. Away from tectonicplate boundaries the geothermal gradient is 25-30C per kilometre(km) of depth in most of the world, and wells would have to be severalkilometres deep to permit electricity generation.[2] The quantity andquality 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 pressurewater. Then they pump water or liquefied carbon dioxide down one borehole, and it comes up the other borehole as agas.[12] This approach is called hot dry rock geothermal energy in Europe, or enhanced geothermal systems in NorthAmerica. Much greater potential may be available from this approach than from conventional tapping of naturalaquifers.[12]

Estimates of the electricity generating potential of geothermal energy vary from 35 to 2000GW depending on thescale of investments.[2] This does not include non-electric heat recovered by co-generation, geothermal heat pumpsand other direct use. A 2006 report by the Massachusetts Institute of Technology (MIT), that included the potentialof enhanced geothermal systems, estimated that investing 1billion USdollars in research and development over15years would allow the creation of 100GW of electrical generating capacity by 2050 in the United States alone.[12]

The MIT report estimated that over 200zettajoules(ZJ) would be extractable, with the potential to increase this toover 2,000ZJ with technology improvements - sufficient to provide all the world's present energy needs for severalmillennia.[12]

At present, geothermal wells are rarely more than 3kilometres (2 mi) deep.[2] Upper estimates of geothermal resources assume wells as deep as 10kilometres (6 mi). Drilling at 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, is 12kilometres (7 mi) deep.[17] This record has recently been imitated by commercial oil wells, such as Exxon's Z-12 well in the Chayvo field, Sakhalin.[18] Wells drilled to depths greater than 4kilometres (2 mi) generally incur drilling

Geothermal electricity 3

costs in the tens of millions of dollars.[19] The technological challenges are to drill wide bores at low cost and tobreak larger volumes of rock.Geothermal power is considered to be sustainable because the heat extraction is small compared to the Earth's heatcontent, but extraction must still be monitored to avoid local depletion.[4] Although geothermal sites are capable ofproviding heat for many decades, individual wells may cool down or run out of water. The three oldest sites, atLarderello, Wairakei, and the Geysers have all reduced production from their peaks. It is not clear whether theseplants extracted energy faster than it was replenished from greater depths, or whether the aquifers supplying them arebeing depleted. If production is reduced, and water is reinjected, these wells could theoretically recover their fullpotential. Such mitigation strategies have already been implemented at some sites. The long-term sustainability ofgeothermal energy has been demonstrated at the Lardarello field in Italy since 1913, at the Wairakei field in NewZealand since 1958,[20] and at The Geysers field in California since 1960.[21]

Power station types

Dry steam plant

Flash steam plant

Dry steam power plantsDry steam plants are the simplest and oldest design. They directly use geothermal steam of 150C or more to turnturbines.[2]

Flash steam power plantsFlash steam plants pull deep, high-pressure hot water into lower-pressure tanks and use the resulting flashed steam todrive turbines. They require fluid temperatures of at least 180C, usually more. This is the most common type ofplant in operation today.[22]

Binary cycle power plantsBinary cycle power plants are the most recent development, and can accept fluid temperatures as low as 57C.[11]

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 to vapor, which then drives the turbines. This is the most common type ofgeothermal electricity plant being built today.[23] Both Organic Rankine and Kalina cycles are used. The thermalefficiency is typically about 10%.

Geothermal electricity 4

Worldwide productionThe International Geothermal Association (IGA) has reported that 10,715 megawatts (MW) of geothermal power in24 countries is online, which is expected to generate 67,246 GWh of electricity in 2010.[1] This represents a 20%increase in geothermal power online capacity since 2005. IGA projects this will grow to 18,500 MW by 2015, due tothe large number of projects presently under consideration, often in areas previously assumed to have littleexploitable resource.[1]

In 2010, the United States led the world in geothermal electricity production with 3,086 MW of installed capacityfrom 77 power plants;[3] the largest group of geothermal power plants in the world is located at The Geysers, ageothermal field in California.[24] The Philippines follows the US as the second highest producer of geothermalpower in the world, with 1,904 MW of capacity online; geothermal power makes up approximately 18% of thecountry's electricity generation.[3]

January 2011: Al Gore said in The Climate Project Asia Pacific Summit that Indonesia could become a super powercountry in electricity production from geothermal energy.[25]

Utility-grade plantsThe largest group of geothermal power plants in the world is located at The Geysers, a geothermal field inCalifornia, United States.[26] As of 2004, five countries (El Salvador, Kenya, the Philippines, Iceland, and CostaRica) generate more than 15% of their electricity from geothermal sources.[2]

Naknek Electric Association (NEA) is going to make an exploration well near King Salmon, in Southwest Alaska. Itcould cut the cost of electricity production by 71 percent and the planned power is 25 megawatts.[27]

Geothermal electricity is generated in the 24 countries listed in the table below. During 2005, contracts were placedfor an additional 500 MW of electrical capacity in the United States, while there were also plants under constructionin 11 other countries.[12] Enhanced geothermal systems that are several kilometres in depth are operational in Franceand Germany and are being developed or evaluated in at least four other countries.

Installed geothermal electric capacity

Country Capacity(MW)

2007[6]

Capacity(MW)

2010[28]

percentageof nationalproduction

USA 2687 3086 0.3%

Philippines 1969.7 1904 27%

Indonesia 992 1197 3.7%

Mexico 953 958 3%

Italy 810.5 843

New Zealand 471.6 628 10%

Iceland 421.2 575 30%

Japan 535.2 536 0.1%

El Salvador 204.2 204 14%

Kenya 128.8 167 11.2%

Costa Rica 162.5 166 14%

Nicaragua 87.4 88 10%

Russia 79 82

Turkey 38 94.2 0.3%

Geothermal electricity 5

Papua-New Guinea 56 56

Guatemala 53 52

Portugal 23 29

China 27.8 24

France 14.7 16

Ethiopia 7.3 7.3

Germany 8.4 6.6

Austria 1.1 1.4

Australia 0.2 1.1

Thailand 0.3 0.3

TOTAL 9,731.9 10,709.7

Environmental impact

Krafla Geothermal Station in northeast Iceland

Fluids drawn from the deep earth carry a mixture of gases, notablycarbon dioxide (CO2), hydrogen sulfide (H2S), methane (CH4) andammonia (NH3). These pollutants contribute to global warming, acidrain, and noxious smells if released. Existing geothermal electric plantsemit an average of 122kg of CO2 per megawatt-hour (MWh) ofelectricity, a small fraction of the emission intensity of conventionalfossil fuel plants.[5] Plants that experience high levels of acids andvolatile chemicals are usually equipped with emission-control systemsto reduce the exhaust. Geothermal plants could theoretically injectthese gases back into the earth, as a form of carbon capture andstorage.

In addition to dissolved gases, hot water from geothermal sources may hold in solution trace amounts of toxicchemicals such as mercury, arsenic, boron, antimony, and salt.[29] These chemicals come out of solution as the watercools, and can cause environmental damage if released. The modern practice of injecting geothermal fluids back intothe Earth to stimulate production has the side benefit of reducing this environmental risk.

Plant construction can adversely affect land stability. Subsidence has occurred in the Wairakei field in NewZealand.[30] Enhanced geothermal systems can trigger earthquakes as part of hydraulic fracturing. The project inBasel, Switzerland was suspended because more than 10,000 seismic events measuring up to 3.4 on the RichterScale occurred over the first 6 days of water injection.[31]

Geothermal has minimal land and freshwater requirements. Geothermal plants use 3.5squarekilometrespergigawatt of electrical production (not capacity) versus 32 and 12squarekilometres for coal facilities and windfarms respectively.[30] They use 20litres of freshwater per MWh versus over 1000litres perMWh for nuclear, coal,or oil.[30]

Geothermal electricity 6

EconomicsGeothermal power requires no fuel, and is therefore immune to fuel cost fluctuations, but capital costs tend to behigh. Drilling accounts for over half the costs, and exploration of deep resources entails significant risks. A typicalwell doublet in Nevada can support 4.5 megawatt (MW) of electricity generation and costs about $10 million to drill,with a 20% failure rate.[19] In total, electrical plant construction and well drilling cost about 2-5million perMW ofelectrical capacity, while the levelised energy cost is 0.04-0.10 perkWh.[6] Enhanced geothermal systems tend tobe on the high side of these ranges, with capital costs above $4million perMW and levelized costs above $0.054perkWh in 2007.[32]

Geothermal power is highly scalable: a large geothermal plant can power entire cities while a smaller power plantcan supply a rural village.[33]

Chevron Corporation is the world's largest private producer of geothermal electricity.[34] The most developedgeothermal field is the Geysers in California. In 2008, this field supported 15 plants, all owned by Calpine, with atotal generating capacity of 725MW.[26]

References[1] Geothermal Energy Association. Geothermal Energy: International Market Update (http:/ / www. geo-energy. org/ pdf/ reports/

GEA_International_Market_Report_Final_May_2010. pdf) May 2010, p. 4-6.[2] Fridleifsson,, Ingvar B.; Bertani, Ruggero; Huenges, Ernst; Lund, John W.; Ragnarsson, Arni; Rybach, Ladislaus (2008-02-11), O. Hohmeyer

and T. Trittin, ed. (pdf), The possible role and contribution of geothermal energy to the mitigation of climate change (http:/ / iga. igg. cnr. it/documenti/ IGA/ Fridleifsson_et_al_IPCC_Geothermal_paper_2008. pdf), Luebeck, Germany, pp.5980, , retrieved 2009-04-06

[3] Geothermal Energy Association. Geothermal Energy: International Market Update (http:/ / www. geo-energy. org/ pdf/ reports/GEA_International_Market_Report_Final_May_2010. pdf) May 2010, p. 7.

[4] Rybach, Ladislaus (September 2007), "Geothermal Sustainability" (http:/ / geoheat. oit. edu/ bulletin/ bull28-3/ art2. pdf), Geo-Heat CentreQuarterly Bulletin (Klamath Falls, Oregon: Oregon Institute of Technology) 28 (3): 27, ISSN0276-1084, , retrieved 2009-05-09

[5] Bertani, Ruggero; Thain, Ian (July 2002), "Geothermal Power Generating Plant CO2 Emission Survey" (http:/ / www. geothermal-energy.org/ documenti/ IGA/ newsletter/ n49. pdf), IGA News (International Geothermal Association) (49): 13, , retrieved 2009-05-13

[6] Bertani, Ruggero (September 2007), "World Geothermal Generation in 2007" (http:/ / geoheat. oit. edu/ bulletin/ bull28-3/ art3. pdf),Geo-Heat Centre Quarterly Bulletin (Klamath Falls, Oregon: Oregon Institute of Technology) 28 (3): 819, ISSN0276-1084, , retrieved2009-04-12

[7] Tiwari, G. N.; Ghosal, M. K. Renewable Energy Resources: Basic Principles and Applications. Alpha Science Int'l Ltd., 2005 ISBN1842651250

[8] http:/ / www. ipenz. org. nz/ heritage/ itemdetail. cfm?itemid=84[9] Lund, J. (September 2004), "100 Years of Geothermal Power Production" (http:/ / geoheat. oit. edu/ bulletin/ bull25-3/ art2. pdf), Geo-Heat

Centre Quarterly Bulletin (Klamath Falls, Oregon: Oregon Institute of Technology) 25 (3): 1119, ISSN0276-1084, , retrieved 2009-04-13[10] McLarty, Lynn; Reed, Marshall J. (October 1992), "The U.S. Geothermal Industry: Three Decades of Growth" (http:/ / geotherm. inel. gov/

publications/ articles/ mclarty/ mclarty-reed. pdf), Energy Sources, Part A: Recovery, Utilization, and Environmental Effects (London: Taylor& Francis) 14 (4): 443455, doi:10.1080/00908319208908739, ISSN1556-7230,

[11] Erkan, K.; Holdmann, G.; Benoit, W.; Blackwell, D. (2008), "Understanding the Chena Hot Springs, Alaska, geothermal system usingtemperature and pressure data" (http:/ / linkinghub. elsevier. com/ retrieve/ pii/ S0375650508000576), Geothermics 37 (6): 565585,doi:10.1016/j.geothermics.2008.09.001, ISSN0375-6505, , retrieved 2009-04-11

[12] Tester, Jefferson W. (Massachusetts Institute of Technology) et al (14MB PDF), The Future of Geothermal Energy (http:/ / geothermal. inel.gov/ publications/ future_of_geothermal_energy. pdf), Impact of Enhanced Geothermal Systems (Egs) on the United States in the 21stCentury: An Assessment, Idaho Falls: Idaho National Laboratory, ISBN0-615-13438-6, , retrieved 2007-02-07

[13] Bertani, Ruggero (2009), "Geothermal Energy: An Overview on Resources and Potential" (http:/ / pangea. stanford. edu/ ERE/ pdf/IGAstandard/ ISS/ 2009Slovakia/ I. 1. Bertani. pdf), Proceedings of the International Conference on National Development of GeothermalEnergy Use, Slovakia,

[14] http:/ / gafoen. com/ site/ index. php?page=geothermalenergy[15] Lund, John W. (2003), "The USA Geothermal Country Update", Geothermics, European Geothermal Conference 2003 (Elsevier Science

Ltd.) 32 (4-6): 409418, doi:10.1016/S0375-6505(03)00053-1, ISSN0375-6505[16] Pollack, H.N.; S. J. Hurter, and J. R. Johnson (1993), "Heat Flow from the Earth's Interior: Analysis of the Global Data Set" (http:/ / www.

agu. org/ pubs/ crossref/ 1993/ 93RG01249. shtml), Rev. Geophys. 30 (3): 267280,[17] Cassino, Adam (2003). "Depth of the Deepest Drilling" (http:/ / hypertextbook. com/ facts/ 2003/ AdamCassino. shtml). The Physics

Factbook. Glenn Elert. . Retrieved 2009-04-09.

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[18] Watkins, Eric (February 11, 2008), "ExxonMobil drills record extended-reach well at Sakhalin-1" (http:/ / www. mapsearch. com/ news/display. html?id=319813), Oil & Gas Journal, , retrieved 2009-10-31

[19] Geothermal Economics 101, Economics of a 35 MW Binary Cycle Geothermal Plant (http:/ / www. glacierpartnerscorp. com/ geothermal.php), New York: Glacier Partners, October 2009, , retrieved 2009-10-17

[20] Thain, Ian A. (September 1998), "A Brief History of the Wairakei Geothermal Power Project" (http:/ / geoheat. oit. edu/ bulletin/ bull19-3/art1. pdf), Geo-Heat Centre Quarterly Bulletin (Klamath Falls, Oregon: Oregon Institute of Technology) 19 (3): 14, ISSN0276-1084, ,retrieved 2009-06-02

[21] Axelsson, Gudni; Stefnsson, Valgardur; Bjrnsson, Grmur; Liu, Jiurong (April 2005), "Sustainable Management of Geothermal Resourcesand Utilization for 100 300 Years" (http:/ / iga. igg. cnr. it/ geoworld/ pdf/ WGC/ 2005/ 0507. pdf), Proceedings World GeothermalCongress 2005 (International Geothermal Association), , retrieved 2009-06-02

[22] US DOE EERE Hydrothermal Power Systems (http:/ / www1. eere. energy. gov/ geothermal/ powerplants. html)[23] "Geothermal Basics Overview" (http:/ / www1. eere. energy. gov/ geothermal/ geothermal_basics. html). Office of Energy Efficiency and

Renewable Energy. . Retrieved 2008-10-01.[24] Khan, M. Ali (2007) (pdf), The Geysers Geothermal Field, an Injection Success Story (http:/ / www. gwpc. org/ meetings/ forum/ 2007/

proceedings/ Papers/ Khan, Ali Paper. pdf), Annual Forum of the Groundwater Protection Council, , retrieved 2010-01-25[25] http:/ / www. antaranews. com/ en/ news/ 1294577958/ indonesia-can-be-super-power-on-geothermal-energy-al-gore[26] Reuters. "Calpine Corporation (CPN) (NYSE Arca) Profile" (http:/ / www. reuters. com/ finance/ stocks/ companyProfile?rpc=66&

symbol=CPN). Press release. . Retrieved 2009-10-14.[27] http:/ / www. renewableenergyworld. com/ rea/ news/ article/ 2009/ 05/

naknek-electric-utility-heats-up-geothermal-plans?cmpid=WNL-Wednesday-May6-2009[28] Holm, Alison (May 2010), Geothermal Energy:International Market Update (http:/ / www. geo-energy. org/ pdf/ reports/

GEA_International_Market_Report_Final_May_2010. pdf), Geothermal Energy Association, pp.7, , retrieved 2010-05-24[29] Bargagli1, R.; Catenil, D.; Nellil, L.; Olmastronil, S.; Zagarese, B. (August 1997), "Environmental Impact of Trace Element Emissions from

Geothermal Power Plants", Environmental Contamination Toxicology (New York: Springer) 33 (2): 172181, doi:10.1007/s002449900239,ISSN0090-4341

[30] Lund, John W. (June 2007), "Characteristics, Development and utilization of geothermal resources" (http:/ / geoheat. oit. edu/ bulletin/bull28-2/ art1. pdf), Geo-Heat Centre Quarterly Bulletin (Klamath Falls, Oregon: Oregon Institute of Technology) 28 (2): 19,ISSN0276-1084, , retrieved 2009-04-16

[31] Deichmann, N. et al (2007), Seismicity Induced by Water Injection for Geothermal Reservoir Stimulation 5km Below the City of Basel,Switzerland (http:/ / adsabs. harvard. edu/ abs/ 2007AGUFM. V53F. . 08D), American Geophysical Union,

[32] Sanyal, Subir K.; Morrow, James W.; Butler, Steven J.; Robertson-Tait, Ann (January 2224, 2007), "Cost of Electricity from EnhancedGeothermal Systems" (http:/ / pangea. stanford. edu/ ERE/ pdf/ IGAstandard/ SGW/ 2007/ sanyal1. pdf), Proc. Thirty-Second Workshop onGeothermal Reservoir Engineering, Stanford, California,

[33] Lund, John W.; Boyd, Tonya (June 1999), "Small Geothermal Power Project Examples" (http:/ / geoheat. oit. edu/ bulletin/ bull20-2/ art2.pdf), Geo-Heat Centre Quarterly Bulletin (Klamath Falls, Oregon: Oregon Institute of Technology) 20 (2): 926, ISSN0276-1084, , retrieved2009-06-02

[34] Davies, Ed; Lema, Karen (June 29, 2008), "Pricey oil makes geothermal projects more attractive for Indonesia and the Philippines" (http:/ /www. nytimes. com/ 2008/ 06/ 29/ business/ worldbusiness/ 29iht-energy. 1. 14068397. html), The New York Times, , retrieved 2009-10-31

External links Articles on Geothermal Energy (http:/ / www. geni. org/ globalenergy/ library/

articles-renewable-energy-transmission/ geothermal. shtml)

Article Sources and Contributors 8

Article Sources and ContributorsGeothermal electricity Source: http://en.wikipedia.org/w/index.php?oldid=412591258 Contributors: Brian PM Taylor, Claus Ableiter, CommonsDelinker, DVdm, E8, ESkog, Elekhh, Glst2,Gsarwa, Id447, Jaeger222, Jncraton, Johnfos, Jusdafax, Lcmortensen, Mnmngb, Nopetro, Plazak, Pyrotec, Rehman, Rjwilmsi, Tea and crumpets, Teratornis, Vrenator, Weltuntergang, Wikipelli,Ytrottier, 30 anonymous edits

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