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Geothermal energy is the
thermal energy The term "thermal energy" is used loosely in various contexts in physics and engineering. It can refer to several different well-defined physical concepts. These include the internal energy or enthalpy of a body of matter and radiation; heat, de ...
in the Earth's crust which originates from the formation of the planet and from radioactive decay of materials in currently uncertain but possibly roughly equal proportions. The high temperature and pressure in Earth's interior cause some rock to melt and solid mantle to behave plastically. This results in parts of the mantle convecting upward since it is lighter than the surrounding rock. Temperatures at the
core–mantle boundary The core–mantle boundary (CMB) of Earth lies between the planet's silicate mantle and its liquid iron-nickel outer core. This boundary is located at approximately 2,891 km (1,796 miles) depth beneath Earth's surface. The boundary is observed ...
can reach over 4000 °C (7200 °F).
Geothermal heating 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 ...
, using water from hot springs, for example, has been used for bathing since Paleolithic times and for
space heating Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
since ancient Roman times. More recently geothermal power, the term used for generation of electricity from geothermal energy, has gained in importance. It is estimated that the earth's geothermal resources are theoretically more than adequate to supply humanity's energy needs, although only a very small fraction is currently being profitably exploited, often in areas near tectonic plate boundaries. As a result of government assisted research and industry experience, the cost of generating geothermal power decreased by 25% over the 1980s and 1990s. More recent technological advances have dramatically reduced costs and thereby expanded the range and size of viable resources. In 2021, the U.S. Department of Energy estimates that geothermal energy from a power plant "built today" costs about $0.05/kWh. In 2019, 13,900
megawatts The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wat ...
(MW) of geothermal power was available worldwide. An additional 28 gigawatts of direct
geothermal heating 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 ...
capacity has been installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications as of 2010. Forecasts for the future of geothermal power depend on assumptions about technology, energy prices, subsidies, plate boundary movement and interest rates. Pilot programs like EWEB's customer opt in Green Power Program show that customers would be willing to pay a little more for a renewable energy source like geothermal. About 100 thousand people are employed in the industry. The adjective ''geothermal'' originates from the Greek roots (), meaning Earth, and (), meaning hot.


History

Hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by c ...
s have been used for bathing at least since Paleolithic times. The oldest known spa is a site where the Huaqing Chi palace was later built. In the first century CE, Romans conquered ''
Aquae Sulis Aquae Sulis (Latin for ''Waters of Sulis'') was a small town in the Roman province of Britannia. Today it is the English city of Bath, Somerset. The Antonine Itinerary register of Roman roads lists the town as ''Aquis Sulis.'' Ptolemy records t ...
'', now Bath, Somerset, England, and used the hot springs there to feed
public baths Public baths originated when most people in population centers did not have access to private bathing facilities. Though termed "public", they have often been restricted according to gender, religious affiliation, personal membership, and other cr ...
and underfloor heating. The admission fees for these baths probably represent the first commercial use of geothermal power. The world's oldest geothermal district heating system in
Chaudes-Aigues Chaudes-Aigues (; oc, Chaudas Aigas, ) is a commune in the Cantal department in south-central France. It is a spa town, famous for its hot spring waters. Geography The commune is situated in the Massif Central in Aubrac. Its inhabitants are ...
, France, has been operating since the 15th century. The earliest industrial exploitation began in 1827 with the use of geyser steam to extract
boric acid Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula . It may also be called hydrogen borate or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolve ...
from
volcanic mud A mud volcano or mud dome is a landform created by the eruption of mud or slurries, water and gases. Several geological processes may cause the formation of mud volcanoes. Mud volcanoes are not true igneous volcanoes as they do not produce la ...
in
Larderello Larderello is a ''frazione'' of the ''comune'' of Pomarance, in Tuscany in central Italy, renowned for its geothermal productivity. Geography The region of Lardarello has experienced occasional phreatic eruptions, caused by explosive outburst ...
, Italy. In 1892, America's first
district heating District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating a ...
system in
Boise, Idaho Boise (, , ) is the capital and most populous city of the U.S. state of Idaho and is the county seat of Ada County. On the Boise River in southwestern Idaho, it is east of the Oregon border and north of the Nevada border. The downtown ar ...
was powered directly by geothermal energy, and was copied in Klamath Falls, Oregon in 1900. The first known building in the world to utilize geothermal energy as its primary heat source was the
Hot Lake Hotel Hot Lake Hotel (also known as Hot Lake Resort) is a historic Colonial Revival hotel originally built in 1864 in Hot Lake, Union County, Oregon, United States. The hotel received its namesake from the thermal spring lakes on the property, and o ...
in
Union County, Oregon Union County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 26,196. Its county seat is La Grande. Union County comprises the La Grande, OR Micropolitan Statistical Area. It is one of the ei ...
, whose construction was completed in 1907. A deep geothermal well was used to heat greenhouses in Boise in 1926, and geysers were used to heat greenhouses in Iceland and
Tuscany it, Toscano (man) it, Toscana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Citizenship , demographics1_footnotes = , demographics1_title1 = Italian , demogra ...
at about the same time. Charlie Lieb developed the first downhole heat exchanger in 1930 to heat his house. Steam and hot water from geysers began heating homes in Iceland starting in 1943. In the 20th century, demand for electricity led to the consideration of geothermal power as a generating source. Prince
Piero Ginori Conti Piero Ginori Conti, Prince of Trevignano, (Florence, 3 June 1865 - Florence, 3 December 1939) was a businessman and Italian politician. Son of Gino Ginori Conti and Pauline Fabbri, an old aristocratic family of Florence, Piero Ginori Conti married ...
tested the first geothermal power generator on 4 July 1904, at the same Larderello dry steam field where geothermal acid extraction began. It successfully lit four light bulbs. Later, in 1911, the world's first commercial geothermal power plant was built there. It was the world's only industrial producer of geothermal electricity until New Zealand built a plant in 1958. In 2012, it produced some 594 megawatts. In 1960, Pacific Gas and Electric began operation of the first successful geothermal electric power plant in the United States at The Geysers in California. The original turbine lasted for more than 30 years and produced 11  MW net power. The binary cycle power plant was first demonstrated in 1967 in the
USSR The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...
and later introduced to the US in 1981. This technology allows the generation of electricity from much lower temperature resources than previously. In 2006, a binary cycle plant in Chena Hot Springs, Alaska, came on-line, producing electricity from a record low fluid temperature of . In 2021 Quaise Energy announced the idea of using a
gyrotron High-power 140 GHz gyrotron for plasma heating in the Wendelstein 7-X fusion experiment, Germany. A gyrotron is a class of high-power linear-beam vacuum tubes that generates millimeter-wave electromagnetic waves by the cyclotron resonance of e ...
as a boring machine to drill a hole 20 kilometers in depth and use it to produce geothermal energy. The technique would use frequencies of 30 to 300 GHz and would transfer energy to a rock 1012 (1 trillion) times more efficiently than using a laser. Lasers would further be disrupted by the vaporized rock, which would effect the longer-wavelength much less. Drilling rates of 70 meters/hour appear to be possible with a 1-MW gyrotron that can achieve 100 percent efficiency.


Resources

The Earth's internal thermal energy flows to the surface by conduction at a rate of 44.2 terawatts (TW), and is replenished by radioactive decay of minerals at a rate of 30 TW. These power rates are more than double humanity's current energy consumption from all primary sources, but most of this energy flow is not recoverable. In addition to the internal heat flows, the top layer of the surface to a depth of is heated by solar energy during the summer, and releases that energy and cools during the winter. Outside of the seasonal variations, the
geothermal gradient Geothermal gradient is the rate of temperature change with respect to increasing depth in Earth's interior. As a general rule, the crust temperature rises with depth due to the heat flow from the much hotter mantle; away from tectonic plate bo ...
of temperatures through the crust is 25–30 °C (45–54 °F) per km of depth in most of the world. The conductive heat flux averages 0.1 MW/km2. These values are much higher near tectonic plate boundaries where the crust is thinner. They may be further augmented by fluid circulation, either through magma conduits, hot springs, hydrothermal circulation or a combination of these. The thermal efficiency and profitability of electricity generation is particularly sensitive to temperature. The most demanding applications receive the greatest benefit from a high natural heat flux, ideally from using a
hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by c ...
. The next best option is to drill a well into a hot aquifer. If no adequate aquifer is available, an artificial one may be built by injecting water to
hydraulically fracture Fracking (also known as hydraulic fracturing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of bedrock formations by a pressurized liquid. The process involves the high-pressure injection of "frack ...
the bedrock. This last 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. Estimates of the potential for electricity generation from geothermal energy vary sixfold, from depending on the scale of investments. Upper estimates of geothermal resources assume enhanced geothermal wells as deep as , whereas existing geothermal wells are rarely more than deep. Wells of this depth are now common in the petroleum industry. The deepest research well in the world, the
Kola superdeep borehole The Kola Superdeep Borehole (russian: Кольская сверхглубокая скважина, translit=Kol'skaya sverkhglubokaya skvazhina) SG-3 is the result of a scientific drilling project of the Soviet Union in the Pechengsky District ...
, is deep.


Geothermal power

Geothermal power is electrical power generated from geothermal energy. Technologies in use include dry steam power stations, flash steam power stations and binary cycle power stations. Geothermal electricity generation is currently used in 26 countries,Geothermal Energy Association
Geothermal Energy: International Market Update
May 2010, p. 4-6.
while
geothermal heating 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 ...
is in use in 70 countries.Moomaw, W., P. Burgherr, G. Heath, M. Lenzen, J. Nyboer, A. Verbruggen
2011: Annex II: Methodology. In IPCC: Special Report on Renewable Energy Sources and Climate Change Mitigation (ref. page 10)
/ref> As of 2019, worldwide geothermal power capacity amounts to 15.4
gigawatt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wat ...
s (GW), of which 23.86 percent or 3.68 GW are installed in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
. 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 14.5–17.6 GW by 2020. Based on current geologic knowledge and technology the GEA publicly discloses, the Geothermal Energy Association (GEA) estimates that only 6.9 percent of total global potential has been tapped so far, while the
IPCC The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) ...
reported geothermal power potential to be in the range of 35 GW to 2  TW. Geothermal energy is a key renewable source that covers a significant share of the electricity demand in countries like
Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...
, El Salvador,
Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi ...
, the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
and
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
, and more than 90 % of the heating demand in Iceland. 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. The
greenhouse gas emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and ...
of geothermal electric stations are on average 45 grams of
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
per kilowatt-hour of electricity, or less than 5 percent of that of conventional coal-fired plants. As a source of renewable energy for both power and heating, geothermal has the potential to meet 3-5% of global demand by 2050. With economic incentives, it is estimated that by 2100 it will be possible to meet 10% of global demand. Geothermal electric plants were traditionally built exclusively on the edges of tectonic plates where high-temperature geothermal resources are available near the surface. The development of binary cycle power plants and improvements in drilling and extraction technology enable enhanced geothermal systems over a much greater geographical range. Demonstration projects are operational in
Landau-Pfalz Landau ( pfl, Landach), officially Landau in der Pfalz, is an autonomous (''kreisfrei'') town surrounded by the Südliche Weinstraße ("Southern Wine Route") district of southern Rhineland-Palatinate, Germany. It is a university town (since 1990) ...
, Germany, and
Soultz-sous-Forêts Soultz-sous-Forêts () is a commune in the Bas-Rhin department in Grand Est in north-eastern France. It is the site of the European Hot Dry Rocks energy research project. Notable people * George Abert, member of the Wisconsin State Assembly ...
, France, while an earlier effort in
Basel , french: link=no, Bâlois(e), it, Basilese , neighboring_municipalities= Allschwil (BL), Hégenheim (FR-68), Binningen (BL), Birsfelden (BL), Bottmingen (BL), Huningue (FR-68), Münchenstein (BL), Muttenz (BL), Reinach (BL), Riehen (BS ...
, Switzerland, was shut down after it triggered earthquakes. Other demonstration projects are under construction in Australia, the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
, and the
United States of America The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territo ...
. In
Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John Wells explai ...
over 39 locations capable of geothermal power production and some of these hydrothermal reservoirs lie quite close to
Yangon Yangon ( my, ရန်ကုန်; ; ), formerly spelled as Rangoon, is the capital of the Yangon Region and the largest city of Myanmar (also known as Burma). Yangon served as the capital of Myanmar until 2006, when the military government ...
which is a significant underutilized resource.


Geothermal heating

Geothermal heating 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 ...
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 In thermodynamics, the thermal efficiency (\eta_) is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, steam turbine, steam engine, boiler, furnace, refrigerator, ACs etc. For a ...
is high since no energy conversion is needed, but
capacity factor The net capacity factor is the unitless ratio of actual electrical energy output over a given period of time to the theoretical maximum electrical energy output over that period. The theoretical maximum energy output of a given installation is def ...
s tend to be low (around 20%) since the heat is mostly needed in the winter. Geothermal energy originates from the heat retained within the Earth since the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface. Most high temperature geothermal heat is harvested in regions close to tectonic plate boundaries where volcanic activity rises close to the surface of the Earth. In these areas, ground and groundwater can be found with temperatures higher than the target temperature of the application. However, even cold ground contains heat, below the undisturbed ground temperature is consistently at the Mean Annual Air Temperature and it may be extracted with a
ground source heat pump A ground source heat pump (also geothermal heat pump) is a heating/cooling system for buildings that uses a type of heat pump to transfer heat to or from the ground, taking advantage of the relative constancy of temperatures of the earth through ...
.


Types

Geothermal energy comes in either ''vapor-dominated'' or ''liquid-dominated'' forms.
Larderello Larderello is a ''frazione'' of the ''comune'' of Pomarance, in Tuscany in central Italy, renowned for its geothermal productivity. Geography The region of Lardarello has experienced occasional phreatic eruptions, caused by explosive outburst ...
and
The Geysers 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 north of San Francisco, California. Geysers produce ...
are vapor-dominated. Vapor-dominated sites offer temperatures from 240 to 300 °C that produce superheated steam.


Liquid-dominated plants

Liquid-dominated reservoirs (LDRs) are more common with temperatures greater than and are found near young volcanoes surrounding the Pacific Ocean and in rift zones and hot spots. ''Flash plants'' are the common way to generate electricity from these sources. Pumps are generally not required, powered instead when the water turns to steam. Most wells generate 2–10 MW of electricity. Steam is separated from a liquid via cyclone separators, while the liquid is returned to the reservoir for reheating/reuse. As of 2013, the largest liquid system is
Cerro Prieto Cerro Prieto ( coc, Wee Ñaay, eng, "Black Hill") is a volcano located approximately 29 km (18 mi) SSE of Mexicali in the Mexican state of Baja California. The volcano lies astride a spreading center associated with the East Pacific R ...
in Mexico, which generates 750 MW of electricity from temperatures reaching . The Salton Sea field in Southern California offers the potential of generating 2000 MW of electricity. Lower-temperature LDRs (120–200 °C) require pumping. They are common in extensional terrains, where heating takes place via deep circulation along faults, such as in the Western US and Turkey. Water passes through a
heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct conta ...
in a
Rankine cycle The Rankine cycle is an idealized thermodynamic cycle describing the process by which certain heat engines, such as steam turbines or reciprocating steam engines, allow mechanical work to be extracted from a fluid as it moves between a heat sourc ...
binary plant. The water vaporizes an organic working fluid that drives a turbine. These binary plants originated in the Soviet Union in the late 1960s and predominate in new US plants. Binary plants have no emissions.


Enhanced geothermal systems

Enhanced geothermal systems (EGS) actively inject water into wells to be heated and pumped back out. The water is injected under high pressure to expand existing rock fissures to enable the water to freely flow in and out. The technique was adapted from oil and gas extraction techniques. However, the geologic formations are deeper and no toxic chemicals are used, reducing the possibility of environmental damage. Drillers can employ directional drilling to expand the size of the reservoir. Small-scale EGS have been installed in the Rhine Graben at
Soultz-sous-Forêts Soultz-sous-Forêts () is a commune in the Bas-Rhin department in Grand Est in north-eastern France. It is the site of the European Hot Dry Rocks energy research project. Notable people * George Abert, member of the Wisconsin State Assembly ...
in France and at Landau and
Insheim Insheim is a municipality in the Verbandsgemeinde Herxheim in the Südliche Weinstraße district in Rhineland-Palatinate. Geography Insheim is a part of the Südpfalz. The township belongs to the Verbandsgemeinde Herxheim. Next to Insheim are ...
in Germany.


Economics

Geothermal power requires no fuel (except for pumps), and is therefore immune to fuel cost fluctuations. However, capital costs are significant. Drilling accounts for over half the costs, and exploration of deep resources entails significant risks. A typical well doublet (extraction and injection wells) in
Nevada Nevada ( ; ) is a state in the Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the 7th-most extensive, ...
can support 4.5
megawatt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...
s (MW) and costs about $10 million to drill, with a 20% failure rate. As noted above, drilling cost is a major component of a geothermal power plant's budget and is one of the key barriers to wider development of geothermal resources. A power plant must have production wells to bring the hot fluid (steam or hot water) to the surface and must also have injection wells to pump the liquid back into the reservoir after it has passed through the power plant. Drilling geothermal wells is more expensive than drilling oil and gas wells of comparable depth for several reasons: * Geothermal reservoirs are usually in igneous or metamorphic rock, which is harder than the sedimentary rock of hydrocarbon reservoirs. * The rock is often fractured, which causes vibrations that are damaging to bits and other drilling tools. * The rock is often abrasive, with high quartz content, and sometimes contains highly corrosive fluids. * The formation is, by definition, hot, which limits use of downhole electronics. * Casing in geothermal wells must be cemented from top to bottom, to resist the casing's tendency to expand and contract with temperature changes. Oil and gas wells are usually cemented only at the bottom. * Because the geothermal well produces a low-value fluid (steam or hot water) its diameter is considerably larger than typical oil and gas wells. In total, electrical plant construction and well drilling cost about €2–5 million per MW of electrical capacity, while the break-even price is 0.04–0.10 € per kW·h. Enhanced geothermal systems tend to be on the high side of these ranges, with capital costs above $4 million per MW and break-even above $0.054 per kW·h in 2007. The capital cost of one such district heating system in
Bavaria Bavaria ( ; ), officially the Free State of Bavaria (german: Freistaat Bayern, link=no ), is a state in the south-east of Germany. With an area of , Bavaria is the largest German state by land area, comprising roughly a fifth of the total lan ...
was estimated at somewhat over 1 million € per MW. Direct systems of any size are much simpler than electric generators and have lower maintenance costs per kW·h, but they must consume electricity to run pumps and compressors. Some governments subsidize geothermal projects. Geothermal power is highly scalable: from a rural village to an entire city, making it a vital part of the renewable energy transition. The most developed geothermal field in the United States is
The Geysers 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 north of San Francisco, California. Geysers produce ...
in Northern California. Geothermal projects have several stages of development. Each phase has associated risks. At the early stages of reconnaissance and geophysical surveys, many projects are canceled, making that phase unsuitable for traditional lending. Projects moving forward from the identification, exploration and exploratory drilling often trade equity for financing.


Renewability and sustainability

Geothermal power is considered to be renewable because any projected heat extraction is small compared to the Earth's heat content. The Earth has an internal heat content of 1031 joules (3·1015  TWh), approximately 100 billion times the 2010 worldwide annual energy consumption. About 20% of this is residual heat from
planetary accretion In astrophysics, accretion is the accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, in an accretion disk. Most astronomical objects, such as galaxies, stars, and planets, are form ...
; the remainder is attributed to past and current radioactive decay of naturally occurring isotopes. For example, a 5275 m deep borehole in United Downs Deep Geothermal Power Project in
Cornwall Cornwall (; kw, Kernow ) is a historic county and ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people. Cornwall is bordered to the north and west by the Atlantic ...
, England, found granite with very high
thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
content, whose radioactive decay is believed to power the high temperature of the rock. Natural heat flows are not in equilibrium, and the planet is slowly cooling down on geologic timescales. Human extraction taps a minute fraction of the natural outflow, often without accelerating it. According to most official descriptions of geothermal energy use, it is currently called renewable and sustainable because it returns an equal volume of water to the area that the heat extraction takes place, but at a somewhat lower temperature. For instance, the water leaving the ground is 300 degrees, and the water returning is 200 degrees, the energy obtained is the difference in heat that is extracted. Current research estimates of impact on the heat loss from the Earth's core are based on a studies done up through 2012. However, if household and industrial uses of this energy source were to expand dramatically over coming years, based on a diminishing fossil fuel supply and a growing world population that is rapidly industrializing requiring additional energy sources, then the estimates on the impact on the Earth's cooling rate would need to be re-evaluated. Geothermal power is also considered to be sustainable thanks to its power to sustain the Earth's intricate ecosystems. By using geothermal sources of energy present generations of humans will not endanger the capability of future generations to use their own resources to the same amount that those energy sources are presently used. Further, due to its low emissions geothermal energy is considered to have excellent potential for mitigation of global warming.
Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...
has so much geothermal energy that even the sidewalks in Reykjavik are heated with it. In winter, this saves the need for gritting. Even though geothermal power is globally sustainable, extraction must still be monitored to avoid local depletion. Over the course of decades, individual wells draw down local temperatures and water levels until a new equilibrium is reached with natural flows. The three oldest sites, at
Larderello Larderello is a ''frazione'' of the ''comune'' of Pomarance, in Tuscany in central Italy, renowned for its geothermal productivity. Geography The region of Lardarello has experienced occasional phreatic eruptions, caused by explosive outburst ...
,
Wairakei Wairakei is a small settlement, and geothermal area a few kilometres north of Taupō, in the centre of the North Island of New Zealand, on the Waikato River. It is part of the Taupō Volcanic Zone and features several natural geysers, hot pool ...
, and the Geysers have experienced reduced output because of local depletion. Heat and water, in uncertain proportions, were extracted faster than they were replenished. 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 Lardarello field in
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
since 1913, at the Wairakei field in
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
since 1958, and at The Geysers field in California since 1960. Falling electricity production may be boosted through drilling additional supply boreholes, as at Poihipi and Ohaaki. The
Wairakei Wairakei is a small settlement, and geothermal area a few kilometres north of Taupō, in the centre of the North Island of New Zealand, on the Waikato River. It is part of the Taupō Volcanic Zone and features several natural geysers, hot pool ...
power station has been running much longer, with its first unit commissioned in November 1958, and it attained its peak generation of 173 MW in 1965, but already the supply of high-pressure steam was faltering, in 1982 being derated to intermediate pressure and the station managing 157 MW. Around the start of the 21st century it was managing about 150 MW, then in 2005 two 8 MW isopentane systems were added, boosting the station's output by about 14 MW. Detailed data are unavailable, being lost due to re-organisations. One such re-organisation in 1996 causes the absence of early data for Poihipi (started 1996), and the gap in 1996/7 for Wairakei and Ohaaki; half-hourly data for Ohaaki's first few months of operation are also missing, as well as for most of Wairakei's history.


Environmental effects

Fluids drawn from the deep Earth carry a mixture of gasses, notably
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
(), hydrogen sulfide (),
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
() and
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
(). These pollutants contribute to
global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
, acid rain, and noxious smells if released. Existing geothermal electric plants emit an average of of per megawatt-hour (MW·h) of electricity, a small fraction of the
emission intensity An emission intensity (also carbon intensity or C.I.) is the emission rate of a given pollutant relative to the intensity of a specific activity, or an industrial production process; for example grams of carbon dioxide released per megajoule o ...
of conventional fossil fuel plants. But a few plants emit more than gas-fired power, at least in the first few years, such as some
geothermal power in Turkey Geothermal energy is a significant part of renewable energy in Turkey: it is used for geothermal heating and generates 3% of Turkey's electricity. Turkey is the world's second largest user of geothermal heating, after China. Many greenhouses, ...
. Plants that experience high levels of acids and volatile chemicals are usually equipped with emission-control systems to reduce the exhaust. In addition to dissolved gases, hot water from geothermal sources may hold in solution trace amounts of toxic elements such as mercury,
arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, ...
, boron, and
antimony Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient t ...
. These chemicals precipitate as the water cools, and can cause environmental damage if released. The modern practice of injecting cooled geothermal fluids back into the 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 New Zealand. In Staufen im Breisgau, Germany,
tectonic uplift Tectonic uplift is the geologic uplift of Earth's surface that is attributed to plate tectonics. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal th ...
occurred instead, due to a previously isolated
anhydrite Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the ...
layer coming in contact with water and turning into gypsum, doubling its volume. Enhanced geothermal systems can trigger
earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...
s as part of hydraulic fracturing. The project in
Basel , french: link=no, Bâlois(e), it, Basilese , neighboring_municipalities= Allschwil (BL), Hégenheim (FR-68), Binningen (BL), Birsfelden (BL), Bottmingen (BL), Huningue (FR-68), Münchenstein (BL), Muttenz (BL), Reinach (BL), Riehen (BS ...
, Switzerland was suspended because more than 10,000 seismic events measuring up to 3.4 on the Richter Scale occurred over the first 6 days of water injection. Geothermal has minimal land and freshwater requirements. Geothermal plants use per gigawatt of electrical production (not capacity) versus and for
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
facilities and wind farms respectively. They use of freshwater per MW·h versus over per MW·h for nuclear, coal, or oil.


Production


Philippines

The
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
began efforts in researching geothermal energy in 1962 when the Philippine Institute of Volcanology and Seismology inspected the geothermal region in Tiwi, Albay. The desire in shifting to geothermal energy was due to the worldwide oil crisis in the 1970s. These efforts led to the construction of the first geothermal power plant in the Philippines in 1977 which is located in Tongonan, Leyte. The development of the geothermal plant in the Tongonan field was made possible due the drilling contract with the New Zealand government in 1972. The Tongonan Geothermal Field (TGF) advanced in growth by adding plants such as Upper Mahiao, Matlibog, and South Sambaloran which resulted in producing 508 MV in the area. By 2008, the TGF was recognized as one of the world's most developed geothermal power plants. As research in geothermal energy progressed, the first geothermal power plant in the Tiwi region operated in 1979 and two other plants followed the area in 1980 and 1982. The Tiwi geothermal field is located about 450 km from Manila, which is on Luzon Island and the country's capital. The three geothermal power plants in the Tiwi region were producing 330 MWe which allowed the Philippines to be next behind the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
and
Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
in geothermal growth. The geological location of the Philippines resulted in volcanic activity, which is a source of geothermal energy, and it became an advantage since it provided resources to further the research. The Philippines has 7 geothermal fields and continues to contribute efforts in utilizing geothermal energy by creating the Philippine Energy Plan 2012-2030, aiming to achieve utilizing 70% of geothermal energy by 2030.


United States

According to the Geothermal Energy Association (GEA) installed geothermal capacity in the United States grew by 5%, or 147.05 MW, since the last annual survey in March 2012. This increase came from seven geothermal projects that began production in 2012. GEA also revised its 2011 estimate of installed capacity upward by 128 MW, bringing current installed U.S. geothermal capacity to 3,386 MW.


See also

* 2010 World Geothermal Congress *
Earth's internal heat budget Earth's internal heat budget is fundamental to the thermal history of the Earth. The flow of heat from Earth's interior to the surface is estimated at 47±2 terawatts (TW)Davies, J. H., & Davies, D. R. (2010). Earth's surface heat flux. Solid ...
* Hydrothermal vent *
International Geothermal Association The International Geothermal Association (IGA) is an international non-profit, non-political, non-governmental association representing the geothermal power sector worldwide. The organisation works for the promotion and worldwide deployment of g ...
* Relative cost of electricity generated by different sources * Renewable energy by country


References


External links


Hawaii Groundwater & Geothermal Resources Center
University of Hawaii at Manoa
Geothermal Resources Council

Energy Efficiency and Renewable Energy – Geothermal Technologies Office

International Energy Agency Geothermal Energy Homepage

NREL – Geothermal Research

2022 discussion of geothermal energy advantages and challenges
{{Authority control Power station technology Sustainable energy Volcanism