Economics
Geothermal power
requires no fuel, and is therefore immune to fuel cost fluctuations,
but 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 megawatt (MW) of
electricity generation 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
levelised energy cost 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 levelized costs above $0.054 per kW·h in
2007.
Geothermal power is highly scalable: a large geothermal
plant can power entire cities while a smaller power plant can supply a
rural village.
Chevron Corporation is the world’s largest private
producer of geothermal electricity. The most developed geothermal field
is the Geysers in California. In 2008, this field supported 15 plants,
all owned by Calpine, with a total generating capacity of 725 MW.
Environmental impact
Fluids
drawn from the deep earth carry a mixture of gases, notably carbon
dioxide (CO2), hydrogen sulfide (H2S), methane (CH4) and ammonia (NH3).
These pollutants contribute to global warming,
acid rain, and noxious smells if released. Existing geothermal electric
plants emit an average of 122 kg of CO2 per megawatt-hour (MW·h) of
electricity, a small fraction of the emission intensity 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.
Geothermal plants 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.
Plant construction can adversely affect
land stability. Subsidence has occurred in the Wairakei field in New
Zealand. Enhanced geothermal systems can trigger earthquakes as part of
hydraulic fracturing. 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.
Geothermal
has minimal land and freshwater requirements. Geothermal plants use 3.5
square kilometres per gigawatt of electrical production (not capacity)
versus 32 and 12 square kilometres for coal facilities and wind farms
respectively.[30] They use 20 litres of freshwater per MW·h versus over
1000 litres per MW·h for nuclear, coal, or oil.
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