Geothermal power

Geothermal power

Overview


Geothermal energy is thermal energy
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

 generated and stored in the Earth. Thermal energy is the energy that determines the temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 of matter. Earth's geothermal energy originates from the original formation of the planet (20%) and from radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...

 of minerals (80%). The geothermal gradient
Geothermal gradient
Geothermal gradient is the rate of increasing temperature with respect to increasing depth in the Earth's interior. Away from tectonic plate boundaries, it is 25–30°C per km of depth in most of the world. Strictly speaking, geo-thermal necessarily refers to the Earth but the concept may be applied...

, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 from the core to the surface.
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Encyclopedia


Geothermal energy is thermal energy
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

 generated and stored in the Earth. Thermal energy is the energy that determines the temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 of matter. Earth's geothermal energy originates from the original formation of the planet (20%) and from radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...

 of minerals (80%). The geothermal gradient
Geothermal gradient
Geothermal gradient is the rate of increasing temperature with respect to increasing depth in the Earth's interior. Away from tectonic plate boundaries, it is 25–30°C per km of depth in most of the world. Strictly speaking, geo-thermal necessarily refers to the Earth but the concept may be applied...

, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 from the core to the surface. The adjective geothermal originates from the Greek roots geo, meaning earth, and thermos, meaning heat.

From hot springs
Hot Springs
Hot Springs may refer to:* Hot Springs, Arkansas** Hot Springs National Park, Arkansas*Hot Springs, California**Hot Springs, Lassen County, California**Hot Springs, Modoc County, California**Hot Springs, Placer County, California...

, geothermal energy has been used for bathing since Paleolithic
Paleolithic
The Paleolithic Age, Era or Period, is a prehistoric period of human history distinguished by the development of the most primitive stone tools discovered , and covers roughly 99% of human technological prehistory...

 times and for space heating
Space heating
A space heater is a self-contained device for heating an enclosed area. Space heating is generally employed to warm a small space, and is usually held in contrast with central heating, which warms many connected spaces at once...

 since ancient Roman times, but it is now better known for electricity generation
Electricity generation
Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...

. Worldwide, about 10,715 megawatts (MW) of geothermal power is online in 24 countries. An additional 28 gigawatts of direct geothermal heating
Geothermal heating
Geothermal heating is the direct use of geothermal energy for 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...

 capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications.

Geothermal power is cost effective, reliable, sustainable, and environmentally friendly, but has historically been limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for applications such as home heating, opening a potential for widespread exploitation. Geothermal wells release greenhouse gases trapped deep within the earth, but these emissions are much lower per energy unit than those of fossil fuels. As a result, geothermal power has the potential to help mitigate global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

 if widely deployed in place of fossil fuels.

The Earth's geothermal resources are theoretically more than adequate to supply humanity's energy needs, but only a very small fraction may be profitably exploited. Drilling and exploration for deep resources is very expensive. Forecasts for the future of geothermal power depend on assumptions about technology, energy prices, subsidies, and interest rates.

History



Hot Springs
Hot Springs
Hot Springs may refer to:* Hot Springs, Arkansas** Hot Springs National Park, Arkansas*Hot Springs, California**Hot Springs, Lassen County, California**Hot Springs, Modoc County, California**Hot Springs, Placer County, California...

 have been used for bathing at least since paleolithic
Paleolithic
The Paleolithic Age, Era or Period, is a prehistoric period of human history distinguished by the development of the most primitive stone tools discovered , and covers roughly 99% of human technological prehistory...

 times The oldest known spa is a stone pool on China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

’s Lisan mountain built in the Qin dynasty
Qin Dynasty
The Qin Dynasty was the first imperial dynasty of China, lasting from 221 to 207 BC. The Qin state derived its name from its heartland of Qin, in modern-day Shaanxi. The strength of the Qin state was greatly increased by the legalist reforms of Shang Yang in the 4th century BC, during the Warring...

 in the 3rd century BC, at the same site where the Huaqing Chi palace was later built. In the first century AD, Romans conquered Aquae Sulis
Aquae Sulis
Aquae Sulis was a small town in the Roman province of Britannia. Today it is known as Bath, located in the English county of Somerset.-Baths and temple complex:...

, now Bath, Somerset, England, and used the hot springs there to feed public baths
Thermae
In ancient Rome, thermae and balnea were facilities for bathing...

 and underfloor heating
Hypocaust
A hypocaust was an ancient Roman system of underfloor heating, used to heat houses with hot air. The word derives from the Ancient Greek hypo meaning "under" and caust-, meaning "burnt"...

. 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
Chaudes-Aigues 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...

, France, has been operating since the 14th century. The earliest industrial exploitation began in 1827 with the use of geyser steam to extract boric acid
Boric acid
Boric acid, also called hydrogen borate or boracic acid or orthoboric acid or acidum boricum, is a weak acid of boron often used as an antiseptic, insecticide, flame retardant, as a neutron absorber, and as a precursor of other chemical compounds. It exists in the form of colorless crystals or a...

 from volcanic mud in Larderello
Larderello
Larderello is a frazione of the comune of Pomarance, in Tuscany in central Italy. It is a geologically active area, renowned for its geothermal productivity.- Geography :...

, Italy.

In 1892, America's first district heating system in Boise, Idaho
Boise, Idaho
Boise is the capital and most populous city of the U.S. state of Idaho, as well as the county seat of Ada County. Located on the Boise River, it anchors the Boise City-Nampa metropolitan area and is the largest city between Salt Lake City, Utah and Portland, Oregon.As of the 2010 Census Bureau,...

 was powered directly by geothermal energy, and was copied in Klamath Falls, Oregon
Klamath Falls, Oregon
Klamath Falls is a city in Klamath County, Oregon, United States. Originally called Linkville when George Nurse founded the town in 1867, after the Link River on whose falls this city sat, although no falls currently exist; the name was changed to Klamath Falls in 1892...

 in 1900. A deep geothermal well was used to heat greenhouses in Boise in 1926, and geysers were used to heat greenhouses in Iceland and Tuscany
Tuscany
Tuscany is a region in Italy. It has an area of about 23,000 square kilometres and a population of about 3.75 million inhabitants. The regional capital is Florence ....

 at about the same time. Charlie Lieb developed the first downhole heat exchanger
Downhole heat exchanger
A downhole heat exchanger, also called a borehole heat exchanger, is a heat exchanger installed inside a borehole. It is used to capture or dissipate heat to or from the ground...

 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
Piero Ginori Conti, Prince of Trevignano, was a businessman and Italian politician.Son of Gino Ginori Conti and Pauline Fabbri, an old aristocratic family of Florence, Piero Ginori Conti married in 1894 Adriana de Larderel , daughter of Count Florestan - nephew of François - and his cousin...

 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.

By this time, Lord Kelvin had already invented the heat pump
Heat pump
A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...

 in 1852, and Heinrich Zoelly
Heinrich Zoelly
Heinrich Zoelly was a Mexican-Swiss engineer. He developed steam turbines and turbine-driven locomotives and patented the geothermal heat pump in 1912.- Life and work :...

 had patented the idea of using it to draw heat from the ground in 1912. But it was not until the late 1940s that the geothermal heat pump was successfully implemented. The earliest one was probably Robert C. Webber's home-made 2.2 kW direct-exchange system, but sources disagree as to the exact timeline of his invention. J. Donald Kroeker designed the first commercial geothermal heat pump to heat the Commonwealth Building (Portland, Oregon)
Commonwealth Building (Portland, Oregon)
The Commonwealth Building is a 14-story commercial office tower in Portland, Oregon, United States, located at 421 SW 6th Avenue between Washington and Stark Streets. Designed by architect Pietro Belluschi, it was built between 1944 and 1948 and was originally known as the Equitable Building...

 and demonstrated it in 1946. Professor Carl Nielsen of Ohio State University
Ohio State University
The Ohio State University, commonly referred to as Ohio State, is a public research university located in Columbus, Ohio. It was originally founded in 1870 as a land-grant university and is currently the third largest university campus in the United States...

 built the first residential open loop version in his home in 1948. The technology became popular in Sweden as a result of the 1973 oil crisis
1973 oil crisis
The 1973 oil crisis started in October 1973, when the members of Organization of Arab Petroleum Exporting Countries or the OAPEC proclaimed an oil embargo. This was "in response to the U.S. decision to re-supply the Israeli military" during the Yom Kippur war. It lasted until March 1974. With the...

, and has been growing slowly in worldwide acceptance since then. The 1979 development of polybutylene
Polybutylene
Polybutylene is a polyolefin or saturated polymer with the chemical formula n. It should not be confused with polybutene, a low molecular weight oligomer with a different repeat unit....

 pipe greatly augmented the heat pump’s economic viability.

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 U.S.S.R. and later introduced to the U.S. 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
Chena Hot Springs, Alaska
Chena Hot Springs is a hot spring, resort, and community in the Fairbanks North Star Borough, Alaska, United States, 56.5 miles northeast of Fairbanks near the Chena River State Recreation Area...

, came on-line, producing electricity from a record low fluid temperature of 57 °C (134.6 °F).

Electricity



The International Geothermal Association (IGA) has reported that 10,715 megawatts (MW) of geothermal power in 24 countries is online, which is expected to generate 67,246 GWh of electricity in 2010. This represents a 20% increase in online capacity since 2005. IGA projects growth to 18,500 MW by 2015, due to the projects presently under consideration, often in areas previously assumed to have little exploitable resource.

In 2010, the United States
Geothermal energy in the United States
Geothermal energy in the United States continues to be an area of considerable activity. In 2010, the United States led the world in geothermal electricity production with 3,086 megawatts of installed capacity from 77 power plants; the largest group of geothermal power plants in the world is...

 led the world in geothermal electricity production with 3,086 MW of installed capacity from 77 power plants. The largest group of geothermal power plants in the world is located at The Geysers
The Geysers
The Geysers is a complex of 22 geothermal power plants, drawing steam from more than 350 wells, located in the Mayacamas Mountains north of San Francisco, California.The largest in the world, the Geysers has...

, a geothermal field in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. The Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

 is the second highest producer, with 1,904 MW of capacity online. Geothermal power makes up approximately 18% of the country's electricity generation.
Installed geothermal electric capacity
Country Capacity (MW)
2007
Capacity (MW)
2010
Percentage
of national
production
USA
Geothermal energy in the United States
Geothermal energy in the United States continues to be an area of considerable activity. In 2010, the United States led the world in geothermal electricity production with 3,086 megawatts of installed capacity from 77 power plants; the largest group of geothermal power plants in the world is...

 
2687 3086 0.3%
Philippines
Geothermal power in the Philippines
The Geothermal Education Office and a 1980 article entitled "The Philippines geothermal success story" by Rudolph J. Birsic published in the journal Geothermal Energy note the remarkable geothermal resources of the Philippines...

 
1969.7 1904 27%
Indonesia
Geothermal power in Indonesia
Geothermal power in Indonesia is an increasingly significant source of renewable energy. As a result of its volcanic geology, Indonesia has 40% of the world's potential geothermal resources, estimated at 28,000 megawatts ....

 
992 1197 3.7%
Mexico  953 958 3%
Italy  810.5 843 1.5%
New Zealand
Geothermal power in New Zealand
Geothermal power in New Zealand is a small but significant part of the energy generation capacity of the country, providing approximately 10% of the country's electricity with installed capacity of over 700 MW...

 
471.6 628 10%
Iceland
Geothermal power in Iceland
Due to the special geological location of Iceland, the high concentration of volcanoes in the area is often an advantage in the generation of geothermal energy, the heating and production of electricity...

 
421.2 575 30%
Japan
Geothermal power in Japan
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....

 
535.2 536 0.1%
Iran  250 250
El Salvador  204.2 204 25%
Kenya
Geothermal power in Kenya
Geothermal power is very cost-effective in the Rift area of Kenya, East Africa. Kenya was the first African country to build geothermal energy sources. Kenya Electricity Generating Company has built two plants, Olkaria I and Olkaria II , with a third private plant Olkaria III...

 
128.8 167 11.2%
Costa Rica  162.5 166 14%
Nicaragua  87.4 88 10%
Russia
Geothermal power in Russia
Russia demonstrated the first single-flash binary cycle power plant at Pauzhetka in 1967 . New two geothermal plants on the north slope of Mutnovsky volcano in Kamchatka, presumably supplying power to Petropavlovsk-Kamchatsky. Another small plants are on Kuril Islands — 1,8 and 2,5 MWe...

 
79 82
Turkey
Geothermal power in Turkey
In 2010 the installed geothermal electricity generation capacity was 100 MWe while direct use installations were approximately 795 MWt.As of 2005, Turkey had the 5th highest direct usage and capacity of geothermal energy in the world. Turkey's capacity as of 2005 is 1495 MWt with a usage of...

 
38 82
Papua-New Guinea  56 56
Guatemala  53 52
Portugal
Geothermal power in Portugal
Portugal's main investment into this type of energy is in the Azores. While electricity is only produced on São Miguel, Azores, direct-use applications are also at Chaves in northern Portugal, at S...

 
23 29
China
Geothermal power in China
-History:Geothermal energy exploitation in China started approximately around 1970. In the socialist planned economy geothermal exploration was handled by national bodies with public investments. Drilled productive wells were transferred free of charge to the final user...

 
27.8 24
France  14.7 16
Ethiopia  7.3 7.3
Germany
Geothermal power in Germany
Electricity from geothermal sources is expected to grow in Germany mainly because a law that benefits the production of geothermal electricity and guarantees a feed-in tariff. Less than 0.4 percent of Germany's total primary energy supply came from geothermal sources in 2004...

 
8.4 6.6
Austria  1.1 1.4
Australia  0.2 1.1
Thailand  0.3 0.3
TOTAL 9,981.9 10,959.7


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
Enhanced geothermal systems
Enhanced Geothermal System is a new type of geothermal power technology that does not require natural convective hydrothermal resources. Until recently, geothermal power systems have exploited only resources where naturally occurring heat, water, and rock permeability are sufficient to allow...

 over a much greater geographical range. Demonstration projects are operational in Landau-Pfalz, Germany, and Soultz-sous-Forêts
Soultz-sous-Forêts
Soultz-sous-Forêts is a commune in the Bas-Rhin department in Alsace in north-eastern France.It is the site of the European Hot Dry Rocks energy research project.-References:*...

, France, while an earlier effort in Basel
Basel
Basel or Basle In the national languages of Switzerland the city is also known as Bâle , Basilea and Basilea is Switzerland's third most populous city with about 166,000 inhabitants. Located where the Swiss, French and German borders meet, Basel also has suburbs in France and Germany...

, Switzerland was shut down after it triggered earthquakes. Other demonstration projects are under construction in Australia, the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, and the United States of America.

The thermal efficiency
Thermal efficiency
In thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example.-Overview:...

 of geothermal electric plants is low, around 10-23%, because geothermal fluids do not reach the high temperatures of steam from boilers. The laws of thermodynamics
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...

 limits the efficiency of heat engines in extracting useful energy. Exhaust heat is wasted, unless it can be used directly and locally, for example in greenhouses, timber mills, and district heating. System efficiency does not materially affect operational costs as it would for plants that use fuel, but it does affect return on the capital used to build the plant. In order to produce more energy than the pumps consume, electricity generation requires relatively hot fields and specialized heat cycles. 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. The global average was 73% in 2005.

Direct application



In the geothermal industry, low temperature means temperatures of 300 °F (148.9 °C) or less. Low-temperature geothermal resources are typically used in direct-use applications, such as district heating
District heating
District heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating...

, greenhouse
Greenhouse
A greenhouse is a building in which plants are grown. These structures range in size from small sheds to very large buildings...

s, fisheries, mineral recovery, and industrial process heating. However, some low-temperature resources can generate electricity using binary cycle electricity generating technology.

Approximately 70 countries made direct use of 270 petajoules (PJ) of geothermal heating
Geothermal heating
Geothermal heating is the direct use of geothermal energy for 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...

 in 2004. More than half went for space heating, and another third for heated pools. The remainder supported industrial and agricultural applications. Global installed capacity was 28 GW, but capacity factors tend to be low (30% on average) since heat is mostly needed in winter. The above figures are dominated by 88 PJ of space heating extracted by an estimated 1.3 million geothermal heat pumps with a total capacity of 15 GW. Heat pumps for home heating are the fastest-growing means of exploiting geothermal energy, with a global annual growth rate of 30% in energy production.

Direct heating is far more efficient than electricity generation and places less demanding temperature requirements on the heat resource. Heat may come from co-generation via a geothermal electrical plant or from smaller wells or heat exchangers buried in shallow ground. As a result, geothermal heating is economic at many more sites than geothermal electricity generation. Where natural hot springs
Hot Springs
Hot Springs may refer to:* Hot Springs, Arkansas** Hot Springs National Park, Arkansas*Hot Springs, California**Hot Springs, Lassen County, California**Hot Springs, Modoc County, California**Hot Springs, Placer County, California...

 are available, the heated water can be piped directly into radiators. If the ground is hot but dry, earth tubes or downhole heat exchanger
Downhole heat exchanger
A downhole heat exchanger, also called a borehole heat exchanger, is a heat exchanger installed inside a borehole. It is used to capture or dissipate heat to or from the ground...

s can collect the heat. But even in areas where the ground is colder than room temperature, heat can still be extracted with a geothermal heat pump more cost-effectively and cleanly than by conventional furnaces. These devices draw on much shallower and colder resources than traditional geothermal techniques, and they frequently combine a variety of functions, including air conditioning
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...

, seasonal energy storage, solar energy collection, and electric heating. Geothermal heat pumps can be used for space heating essentially anywhere.

Geothermal heat supports many applications. District heating
District heating
District heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating...

 applications use networks of piped hot water to heat many buildings across entire communities. In Reykjavík
Reykjavík
Reykjavík is the capital and largest city in Iceland.Its latitude at 64°08' N makes it the world's northernmost capital of a sovereign state. It is located in southwestern Iceland, on the southern shore of Faxaflói Bay...

, Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

, spent water from the district heating system is piped below pavement and sidewalks to melt snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...

. Geothermal desalination
Geothermal desalination
Geothermal desalination is a process under development for the production of fresh water using heat energy. Claimed benefits of this method of desalination are that it requires less maintenance than reverse osmosis membranes and that the primary energy input is from geothermal heat, which is a...

 has been demonstrated.

Economics


Geothermal power requires no fuel (except for pumps), and is therefore immune to fuel cost fluctuations, but 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
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...

 can support 4.5 megawatts (MW) and costs about $10 million to drill, with a 20% failure rate.

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. Direct heating applications can use much shallower wells with lower temperatures, so smaller systems with lower costs and risks are feasible. Residential geothermal heat pumps with a capacity of 10 kilowatt (kW) are routinely installed for around $1–3,000 per kilowatt. District heating systems may benefit from economies of scale if demand is geographically dense, as in cities, but otherwise piping installation dominates capital costs. The capital cost of one such district heating system in Bavaria
Bavaria
Bavaria, formally the Free State of Bavaria is a state of Germany, located in the southeast of Germany. With an area of , it is the largest state by area, forming almost 20% of the total land area of Germany...

 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.

Chevron Corporation
Chevron Corporation
Chevron Corporation is an American multinational energy corporation headquartered in San Ramon, California, United States and active in more than 180 countries. It is engaged in every aspect of the oil, gas, and geothermal energy industries, including exploration and production; refining,...

 is the world's largest private geothermal electricity producer. The most developed geothermal field is the Geysers
The Geysers
The Geysers is a complex of 22 geothermal power plants, drawing steam from more than 350 wells, located in the Mayacamas Mountains north of San Francisco, California.The largest in the world, the Geysers has...

 in California.

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 10 metres (32.8 ft) 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
Geothermal gradient is the rate of increasing temperature with respect to increasing depth in the Earth's interior. Away from tectonic plate boundaries, it is 25–30°C per km of depth in most of the world. Strictly speaking, geo-thermal necessarily refers to the Earth but the concept may be applied...

 of temperatures through the crust is 25 – per kilometer of depth in most of the world. The conductive heat flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...

 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
Hot Springs
Hot Springs may refer to:* Hot Springs, Arkansas** Hot Springs National Park, Arkansas*Hot Springs, California**Hot Springs, Lassen County, California**Hot Springs, Modoc County, California**Hot Springs, Placer County, California...

, hydrothermal circulation
Hydrothermal circulation
Hydrothermal circulation in its most general sense is the circulation of hot water; 'hydros' in the Greek meaning water and 'thermos' meaning heat. Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust...

 or a combination of these.

A geothermal heat pump can extract enough heat from shallow ground anywhere in the world to provide home heating, but industrial applications need the higher temperatures of deep resources. The thermal efficiency and profitability of electricity generation is particularly sensitive to temperature. The more demanding applications receive the greatest benefit from a high natural heat flux, ideally from using a hot spring
Hot spring
A hot spring is a spring that is produced by the emergence of geothermally heated groundwater from the Earth's crust. There are geothermal hot springs in many locations all over the crust of the earth.-Definitions:...

. The next best option is to drill a well into a hot aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...

. If no adequate aquifer is available, an artificial one may be built by injecting water to hydraulically fracture the bedrock. This last approach is called hot dry rock geothermal energy in Europe, or enhanced geothermal systems
Enhanced geothermal systems
Enhanced Geothermal System is a new type of geothermal power technology that does not require natural convective hydrothermal resources. Until recently, geothermal power systems have exploited only resources where naturally occurring heat, water, and rock permeability are sufficient to allow...

 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 10 kilometres (6 mi), whereas existing geothermal wells are rarely more than 3 kilometres (2 mi) deep. Wells of this depth are now common in the petroleum industry. The deepest research well in the world, the Kola superdeep borehole
Kola Superdeep Borehole
The Kola Superdeep Borehole is the result of a scientific drilling project of the Soviet Union in Kola Peninsula. The project attempted to drill as deep as possible into the Earth's crust. Drilling began on 24 May 1970 using the Uralmash-4E, and later the Uralmash-15000 series drilling rig. A...

, is 12 kilometres (7 mi) deep. This record has recently been imitated by commercial oil wells, such as Exxon
Exxon
Exxon is a chain of gas stations as well as a brand of motor fuel and related products by ExxonMobil. From 1972 to 1999, Exxon was the corporate name of the company previously known as Standard Oil Company of New Jersey or Jersey Standard....

's Z-12 well in the Chayvo field, Sakhalin
Sakhalin-I
The Sakhalin-I project, a sister project to Sakhalin-II, is a consortium to locate and produce oil and gas on Sakhalin Island and immediately offshore, in the Okhotsk Sea, from three fields: Chayvo, Odoptu, and Arkutun-Dagi....

.

Sustainability


Geothermal power is considered to be sustainable
Sustainability
Sustainability is the capacity to endure. For humans, sustainability is the long-term maintenance of well being, which has environmental, economic, and social dimensions, and encompasses the concept of union, an interdependent relationship and mutual responsible position with all living and non...

 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 TW·hr). About 20% of this is residual heat from planetary accretion
Gravitational binding energy
The gravitational binding energy of an object consisting of loose material, held together by gravity alone, is the amount of energy required to pull all of the material apart, to infinity...

, and the remainder is attributed to higher radioactive decay rates that existed in the past. 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.

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
Larderello is a frazione of the comune of Pomarance, in Tuscany in central Italy. It is a geologically active area, renowned for its geothermal productivity.- Geography :...

, Wairakei
Wairakei
Wairakei is the name of a power station, small settlement and a geothermal area a few kilometres north of Taupo, in the centre of the North Island of New Zealand, on the Waikato River.- Geothermal field :...

, 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
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

 since 1913, at the Wairakei field in New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

 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
Poihipi Power Station
The Poihipi Power Station is a geothermal power station owned and operated by Contact Energy. It is located on Poihipi Road near Taupo in New Zealand....

 and Ohaaki
Ohaaki Power Station
The Ohaaki Power Station is a geothermal power station owned and operated by Contact Energy. A distinctive feature of this power station is the 105 m high natural draft cooling tower, the only one of its kind in New Zealand....

. The Wairakei
Wairakei Power Station
The Wairakei Power Station is a geothermal power station near the Wairakei Geothermal Field in New Zealand. Wairakei lies in the Taupo Volcanic Zone.- History :...

 power station has been running much longer, with its first unit commissioned in November 1958, and it attained its peak generation of 173MW in 1965, but already the supply of high-pressure steam was faltering, in 1982 being derated to intermediate pressure and the station managing 157MW. At the turn of the century it was managing about 150MW, then in 2005 two 8MW isopentane systems were added, boosting the station's output by about 14MW. 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 gases, notably carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 , hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

 , methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

  and ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 . These pollutants contribute to global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

, acid rain
Acid rain
Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions . It can have harmful effects on plants, aquatic animals, and infrastructure. Acid rain is caused by emissions of carbon dioxide, sulfur dioxide and nitrogen...

, and noxious smells if released. Existing geothermal electric plants emit an average of 122 kilograms (269 lb) of per megawatt-hour (MW·h) of electricity, a small fraction of the emission intensity
Emission intensity
An emission intensity is the average emission rate of a given pollutant from a given source relative to the intensity of a specific activity; for example grams of carbon dioxide released per megajoule of energy produced, or the ratio of greenhouse gas emissions produced to GDP...

 of conventional fossil fuel plants. 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 chemicals such as mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

, arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...

, boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

, and antimony
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...

. 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.

Direct geothermal heating systems contain pumps and compressors, which may consume energy from a polluting source. This parasitic load
Parasitic load
Parasitic load is a term used with regard to electrical appliances and railway locomotives.With regard to electrical appliances, it represents the power consumed even when the appliance is shut off, that is standby power....

 is normally a fraction of the heat output, so it is always less polluting than electric heating. However, if the electricity is produced by burning fossil fuels, then the net emissions of geothermal heating may be comparable to directly burning the fuel for heat. For example, a geothermal heat pump powered by electricity from a combined cycle
Combined cycle
In electric power generation a combined cycle is an assembly of heat engines that work in tandem off the same source of heat, converting it into mechanical energy, which in turn usually drives electrical generators...

 natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 plant would produce about as much pollution as a natural gas condensing furnace of the same size. Therefore the environmental value of direct geothermal heating applications is highly dependent on the emissions intensity of the neighboring electric grid.

Plant construction can adversely affect land stability. Subsidence has occurred in the Wairakei field in New Zealand and in Staufen im Breisgau, Germany. Enhanced geothermal systems
Enhanced geothermal systems
Enhanced Geothermal System is a new type of geothermal power technology that does not require natural convective hydrothermal resources. Until recently, geothermal power systems have exploited only resources where naturally occurring heat, water, and rock permeability are sufficient to allow...

 can trigger earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

s as part of hydraulic fracturing
Hydraulic fracturing
Considerable controversy surrounds the current implementation of hydraulic fracturing technology in the United States. Hydraulic fracturing, or fracking, is the process of utilizing pressurized water, or some other liquid, to fracture rock layers and release petroleum, natural gas, or other...

. The project in Basel
Basel
Basel or Basle In the national languages of Switzerland the city is also known as Bâle , Basilea and Basilea is Switzerland's third most populous city with about 166,000 inhabitants. Located where the Swiss, French and German borders meet, Basel also has suburbs in France and Germany...

, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

 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 3.5 square kilometres (1.4 sq mi) per gigawatt of electrical production (not capacity) versus 32 square kilometres (12.4 sq mi) and 12 square kilometres (4.6 sq mi) for coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 facilities and wind farm
Wind farm
A wind farm is a group of wind turbines in the same location used to produce electric power. A large wind farm may consist of several hundred individual wind turbines, and cover an extended area of hundreds of square miles, but the land between the turbines may be used for agricultural or other...

s respectively. They use 20 litres (5.3 US gal) of freshwater per MW·h versus over 1000 litres (264.2 US gal) per MW·h for nuclear, coal, or oil.

See also


  • Relative cost of electricity generated by different sources
  • 2010 World Geothermal Congress

External links