Geothermal power is power generated by 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 24 countries, while geothermal heating is in use
in 70 countries.
As of 2015, worldwide geothermal power capacity amounts to 12.8
gigawatts (GW), of which 28 percent or 3,548 megawatts are installed
in the United States. 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
Geothermal Energy Association
Geothermal Energy Association (GEA) estimates that only
6.5 percent of total global potential has been tapped so far, while
IPCC reported geothermal power potential to be in the range of
35 GW to 2 TW. Countries generating more than 15 percent
of their electricity from geothermal sources include El Salvador,
Kenya, the Philippines, Iceland and Costa Rica.
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 of geothermal
electric stations are on average 45 grams of carbon dioxide per
kilowatt-hour of electricity, or less than 5 percent of that of
conventional coal-fired plants.
1 History and development
3 Power station types
3.1 Dry steam power stations
3.2 Flash steam power stations
Binary cycle power stations
4 Worldwide production
4.1 Utility-grade stations
5 Environmental impact
7 See also
9 External links
History and development
In the 20th century, demand for electricity led to the
consideration of geothermal power as a generating source. Prince Piero
Ginori Conti tested the first geothermal power generator on 4 July
1904 in Larderello, Italy. It successfully lit four light bulbs.
Later, in 1911, the world's first commercial geothermal power station
was built there. Experimental generators were built in Beppu, Japan
and the Geysers, California, in the 1920s, but Italy was the world's
only industrial producer of geothermal electricity until 1958.
Trends in the top five geothermal electricity-generating countries,
1980–2012 (US EIA)
Global geothermal electric capacity. Upper red line is installed
capacity; lower green line is realized production.
In 1958, New Zealand became the second major industrial producer of
geothermal electricity when its Wairakei station was commissioned.
Wairakei was the first station to use flash steam technology.
Pacific Gas and Electric
Pacific Gas and Electric began operation of the first
successful geothermal electric power station 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 station was first demonstrated in 1967 in
Russia and later introduced to the USA in 1981, following the 1970s
energy crisis and significant changes in regulatory policies. This
technology allows the use of much lower temperature resources than
were previously recoverable. In 2006, a binary cycle station in Chena
Hot Springs, Alaska, came on-line, producing electricity from a record
low fluid temperature of 57 °C (135 °F).
Geothermal electric stations have until recently been built
exclusively where high temperature geothermal resources are available
near the surface. The development of binary cycle power plants and
improvements in drilling and extraction technology may enable enhanced
geothermal systems over a much greater geographical range.
Demonstration projects are operational in Landau-Pfalz, Germany, and
Soultz-sous-Forêts, France, while an earlier effort in Basel,
Switzerland was shut down after it triggered earthquakes. Other
demonstration projects are under construction in Australia, the United
Kingdom, and the United States of America.
The thermal efficiency of geothermal electric stations is low, around
7–10%, because geothermal fluids are at a low temperature
compared with steam from boilers. By the laws of thermodynamics this
low temperature limits the efficiency of heat engines in extracting
useful energy during the generation of electricity. Exhaust heat is
wasted, unless it can be used directly and locally, for example in
greenhouses, timber mills, and district heating. The efficiency of the
system does not affect operational costs as it would for a coal or
other fossil fuel plant, but it does factor into the viability of the
station. In order to produce more energy than the pumps consume,
electricity generation requires high temperature geothermal fields and
specialized heat cycles. 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. However the global average capacity factor was
74.5% in 2008, according to the IPCC.
Enhanced geothermal system
Enhanced geothermal system 1:Reservoir 2:Pump house
3:Heat exchanger 4:Turbine hall 5:Production well
6:Injection well 7:Hot water to district heating
8:Porous sediments 9:Observation well
The Earth’s heat content is about 1031 joules. This heat
naturally flows to the surface by conduction at a rate of 44.2
terawatts (TW) and is replenished by radioactive decay at a rate
of 30 TW. These power rates are more than double humanity’s
current energy consumption from primary sources, but most of this
power is too diffuse (approximately 0.1 W/m2 on average) to be
Earth's crust effectively acts as a thick insulating
blanket which must be pierced by fluid conduits (of magma, water or
other) to release the heat underneath.
Electricity generation requires high-temperature resources that can
only come from deep underground. The heat must be carried to the
surface by fluid circulation, either through magma conduits, hot
springs, hydrothermal circulation, oil wells, drilled water wells, or
a combination of these. This circulation sometimes exists naturally
where the crust is thin: magma conduits bring heat close to the
surface, and hot springs bring the heat to the surface. If no hot
spring is available, a well must be drilled into a hot aquifer. Away
from tectonic plate boundaries the geothermal gradient is
25–30 °C per kilometre (km) of depth in most of the world, so
wells would have to be several kilometres deep to permit electricity
generation. The quantity and quality of recoverable resources
improves with drilling depth and proximity to tectonic plate
In ground that is hot but dry, or where water pressure is inadequate,
injected fluid can stimulate production. Developers bore two holes
into a candidate site, and fracture the rock between them with
explosives or high-pressure water. Then they pump water or liquefied
carbon dioxide down one borehole, and it comes up the other borehole
as a gas. This approach is called hot dry rock geothermal energy
in Europe, or enhanced geothermal systems in North America. Much
greater potential may be available from this approach than from
conventional tapping of natural aquifers.
Estimates of the electricity generating potential of geothermal energy
vary from 35 to 2000 GW depending on the scale of investments.
This does not include non-electric heat recovered by co-generation,
geothermal heat pumps and other direct use. A 2006 report by the
Massachusetts Institute of Technology
Massachusetts Institute of Technology (MIT) that included the
potential of enhanced geothermal systems estimated that investing
1 billion US dollars in research and development over
15 years would allow the creation of 100 GW of electrical
generating capacity by 2050 in the United States alone. The MIT
report estimated that over 200 zettajoules (ZJ) would be
extractable, with the potential to increase this to over 2,000 ZJ
with technology improvements – sufficient to provide all the world's
present energy needs for several millennia.
At present, geothermal wells are rarely more than 3 kilometres
(1.9 mi) deep. Upper estimates of geothermal resources assume
wells as deep as 10 kilometres (6.2 mi). Drilling near this depth
is now possible in the petroleum industry, although it is an expensive
process. The deepest research well in the world, the Kola superdeep
borehole, is 12.3 km (7.6 mi) deep. This record has
recently been imitated by commercial oil wells, such as Exxon's Z-12
well in the Chayvo field, Sakhalin. Wells drilled to depths
greater than 4 kilometres (2.5 mi) generally incur drilling costs
in the tens of millions of dollars. The technological challenges
are to drill wide bores at low cost and to break larger volumes of
Geothermal power is considered to be sustainable because the heat
extraction is small compared to the Earth's heat content, but
extraction must still be monitored to avoid local depletion.
Although geothermal sites are capable of providing heat for many
decades, individual wells may cool down or run out of water. The three
oldest sites, at Larderello, Wairakei, and the Geysers have all
reduced production from their peaks. It is not clear whether these
stations extracted energy faster than it was replenished from greater
depths, or whether the aquifers supplying them are being depleted. If
production is reduced, and water is reinjected, these wells could
theoretically recover their full potential. Such mitigation strategies
have already been implemented at some sites. The long-term
sustainability of geothermal energy has been demonstrated at the
Lardarello field in Italy since 1913, at the
Wairakei field in New
Zealand since 1958, and at
The Geysers field in
Power station types
Dry steam (left), flash steam (centre), and binary cycle (right) power
Geothermal power stations are similar to other steam turbine thermal
power stations in that heat from a fuel source (in geothermal's case,
the Earth's core) is used to heat water or another working fluid. The
working fluid is then used to turn a turbine of a generator, thereby
producing electricity. The fluid is then cooled and returned to the
Dry steam power stations
Dry steam stations are the simplest and oldest design. This type of
power station is not found very often but is the most efficient. There
are little emissions produced and have a simpler design to them.
In these sites no water is produced but instead only the steam from
that water.  Dry Steam Power directly uses geothermal steam of
150 °C or greater to turn turbines. As the turbine rotates it
powers a generator which then produces electricity and ads to the
power field.  Then, the steam is emitted to a condenser. Here the
steam turns back into a liquid which then cools the water. After
the water is cooled it flows down a pipe that emerges back into the
Flash steam power stations
Flash steam stations pull deep, high-pressure hot water into
lower-pressure tanks and use the resulting flashed steam to drive
turbines. They require fluid temperatures of at least 180 °C,
usually more. This is the most common type of station in operation
today. Flash steam plants use geothermal reservoirs of water with
temperatures greater than 360 °F (182 °C). The hot water
flows up through wells in the ground under its own pressure. As it
flows upward, the pressure decreases and some of the hot water boils
into steam. The steam is then separated from the water and used to
power a turbine/generator. Any leftover water and condensed steam may
be injected back into the reservoir, making this a potentially
sustainable resource.  At
The Geysers in California, twenty
years of power production had depleted the groundwater and operations
were substantially reduced. To restore some of the former capacity,
water injection was developed.
Binary cycle power stations
Main article: Binary cycle
Binary cycle power stations are the most recent development, and can
accept fluid temperatures as low as 57 °C. The moderately
hot geothermal water is passed by a secondary fluid with a much lower
boiling point than water. This causes the secondary fluid to flash
vaporize, which then drives the turbines. This is the most common type
of geothermal electricity station being constructed today. Both
Organic Rankine and Kalina cycles are used. The thermal efficiency of
this type station is typically about 10–13%.
Larderello Geothermal Station, in Italy
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 geothermal power online capacity
since 2005. IGA projected this would grow to 18,500 MW by 2015, due to
the large number of projects that were under consideration, often in
areas previously assumed to have little exploitable resource.
In 2010, the United States led the world in geothermal electricity
production with 3,086 MW of installed capacity from 77 power
stations; the largest group of geothermal power plants in the
world is located at The Geysers, a geothermal field in California.
Philippines follows the US as the second highest producer of
geothermal power in the world, with 1,904 MW of capacity online;
geothermal power makes up approximately 27% of the country's
Al Gore said in The Climate Project Asia Pacific Summit that Indonesia
could become a super power country in electricity production from
geothermal energy. India has announced a plan to develop the
country's first geothermal power facility in Chhattisgarh.
Canada is the only major country on the
Pacific Ring of Fire
Pacific Ring of Fire which has
not yet developed geothermal power. The region of greatest potential
is the Canadian Cordillera, stretching from
British Columbia to the
Yukon, where estimates of generating output have ranged from 1,550 MW
to 5,000 MW.
A geothermal power station in Negros Oriental, Philippines.
The largest group of geothermal power plants in the world is located
at The Geysers, a geothermal field in California, United States.
As of 2004, five countries (El Salvador, Kenya, the Philippines,
Iceland, and Costa Rica) generate more than 15% of their electricity
from geothermal sources.
Geothermal electricity is generated in the 24 countries listed in the
table below. During 2005, contracts were placed for an additional 500
MW of electrical capacity in the United States, while there were also
stations under construction in 11 other countries. Enhanced
geothermal systems that are several kilometres in depth are
operational in France and Germany and are being developed or evaluated
in at least four other countries.
Installed geothermal electric capacity
Share of national
Papua New Guinea
MWe Nesjavellir power station in southwest Iceland
Fluids drawn from the deep earth carry a mixture of gases, notably
carbon dioxide (CO
2), hydrogen sulfide (H
2S), methane (CH
4), ammonia (NH
3) and radon (Rn). These pollutants contribute to global warming, acid
rain, radiation and noxious smells if released.[not in citation given]
Existing geothermal electric stations, that fall within the 50th
percentile of all total life cycle emissions studies reviewed by the
IPCC, produce on average 45 kg of CO
2 equivalent emissions per megawatt-hour of generated electricity (kg
2eq/MW·h). For comparison, a coal-fired power plant emits
1,001 kg of CO
2 per megawatt-hour when not coupled with carbon capture and storage
Stations that experience high levels of acids and volatile chemicals
are usually equipped with emission-control systems to reduce the
exhaust. Geothermal stations could theoretically inject these gases
back into the earth, as a form of carbon capture and storage.
In addition to dissolved gases, hot water from geothermal sources may
hold in solution trace amounts of toxic chemicals, such as mercury,
arsenic, boron, antimony, and salt. These chemicals come out of
solution as the water cools, and can cause environmental damage if
released. The modern practice of injecting geothermal fluids back into
the Earth to stimulate production has the side benefit of reducing
this environmental risk.
Station construction can adversely affect land stability. Subsidence
has occurred in the
Wairakei field in New Zealand. Enhanced
geothermal systems can trigger earthquakes due to water injection. The
project in Basel,
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. The risk of geothermal
drilling leading to uplift has been experienced in Staufen im
Geothermal has minimal land and freshwater requirements. Geothermal
stations use 404 square meters per GW·h versus 3,632
and 1,335 square meters for coal facilities and wind farms
respectively. They use 20 litres of freshwater per MW·h
versus over 1000 litres per MW·h for nuclear, coal, or
Geothermal power stations can also disrupt the natural cycles of
geysers. For example, the
Beowawe, Nevada geysers, which were uncapped
geothermal wells, stopped erupting due to the development of the
Geothermal power requires no fuel; it is therefore immune to fuel cost
fluctuations. However, capital costs tend to be high. Drilling
accounts for over half the costs, and exploration of deep resources
entails significant risks. A typical well doublet in Nevada can
support 4.5 megawatts (MW) of electricity generation and costs about
$10 million to drill, with a 20% failure rate. In total,
electrical station construction and well drilling costs about
2–5 million € per MW of electrical capacity, while
the levelised energy cost is 0.04–0.10 € per kW·h.
Enhanced geothermal systems
Enhanced geothermal systems tend to be on the high side of these
ranges, with capital costs above $4 million per MW and
levelized costs above $0.054 per kW·h in 2007.
Geothermal power is highly scalable: a small power station can supply
a rural village, though initial capital costs can be high.
The most developed geothermal field is the Geysers in California. In
2008, this field supported 15 stations, all owned by Calpine, with a
total generating capacity of 725 MW.
Renewable energy portal
Enhanced geothermal system
Iceland Deep Drilling Project
Renewable energy by country
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