What is geothermal energy? Geothermal energy is heat energy

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Geothermal Energy

• What is geothermal energy?
• Geothermal energy is heat energy originating deep
  in the earths molten interior.
• It is this heat energy which is responsible for
  tectonic plates, volcanoes and earthquakes.
• The temperature in the earths interior is as
  high as 7000 C, decreasing to 650 - 1200 C at
  depths of 80km-100km.
• Through the deep circulation of groundwater and
  the intrusion of molten magma into the earths
  crust to depths of only 1km-5km, heat is brought
  closer to the earths surface. The hot molten
  rock heats the surrounding groundwater, which is
  forced to the surface in certain areas in the
  form of hot steam or water. The heat energy close
  to, or at, the earths surface can be utilised as
  a source of energy, namely geothermal energy.

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Country year 1990 1995 1998 World
wide geothermal capacity Argentina 0.67
0.67 0.00 by country. Australia
0.00 0.17 0.40 Greece
0.00 0.00 0.00 (energy output is
in Mega Watts) Guatemala 0.00 0.00
5.00 Indonesia 144.75 309.75 589.50
Italy 545.00 631.70
768.50 Mexico 700.00 753.00 743.00
USA 2774.6 2816.7
2850.0 Total 5866.72 6796.98
8240.0 (Total for 21 countries)
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Geothermal Resources There are four types of
geothermal resources hydrothermal, geopressured,
hot dry rock and magma. Only hydrothermal is
commercially exploited. Hydrothermal Hydrothermal
, or hot water, resources arise, when hot water
and/or steam is formed in fractured or porous
rock at shallow to moderate depths (100m to
4.5km) as a result of either the intrusion in the
earths crust of molten magma from the earths
interior, or the deep circulation of water
through a fault or fracture. Geopressured
Geopressured geothermal resources consist of hot
brine saturated with methane, found in large,
deep aquifers under high pressure. The water and
methane is trapped in sedimentary formations at a
depth of about 3km-6km. Hot Dry Rock Hot dry
rock (HDR) is a heated geological formation
formed in the same way as hydrothermal resources,
but containing no water as the aquifers or
fractures required to conduct water to the
surface are not present. This resource is
virtually limitless and is more accessible than
hydrothermal resources. Magma Magma, the
largest geothermal resource, is molten rock found
at depths of 3km-10km and deeper, and therefore
not easily accessible
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Utilisation of geothermal energy
Geothermal energy can be utilised in two ways
direct heat or electricity generation. Direct
Heat Hydrothermal resources of low to moderate
temperature (20 -150 C) are utilised to
provide direct heating for a range of
applications in the residential, commercial and
industrial sectors. Direct-use geothermal
systems usually consist of a production facility
(eg a well) to convey the heated water to the
surface, a mechanical system (eg piping, heat
exchanger, pump, controls) to convey the heat
energy to where it is required, and a disposal
system (eg injection well or storage pond) to
receive the cooled fluid. Electricity
generation High temperature geothermal resources
can be used for electricity production. There is
currently over 8GW of installed geothermal
electricity generation capacity worldwide. There
are a number of energy conversion technologies,
which use the geothermal resource. These include
dry steam, flash steam and binary cycle systems.
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• Benefits of geothermal energy
• Geothermal energy is an abundant, secure, and, if
  properly utilised, a renewable source of energy.
• Geothermal technologies, using modern emission
  controls, have minimal environmental impact.
  Modern geothermal plants emit less than 0.2 of
  the carbon dioxide of the cleanest fossil fuel
  plant, less than 1 of the sulphur dioxide and
  less than 0.1 of the particulates (Brown 1996).
  Geothermal plants are therefore a viable
  alternative to conventional fossil fuel plants,
  particularly with respect to greenhouse gas
  emissions. Geothermal energy is not associated
  with environmental impacts such as acid rain,
  mine spoils, open pits, oil spills, radioactive
  waste disposal or the damming of rivers.
• Geothermal power stations are very reliable
  compared to conventional power plants. They have
  a high availability and capacity factor.
  Geothermal power plants are designed to run 24
  hours a day, and operation is independent of the
  weather or fuel delivery.
• Geothermal power generation technologies are
  modular in design and highly flexible. The output
  of a geothermal plant can be expanded as
  required, avoiding the need for a high initial
  capital outlay. The plants have short lead times
  of 1 to 2 years.
• Geothermal resources represent an indigenous
  supply of energy, providing energy supply
  security, reducing the need for fuel imports, and
  improving the balance of payments. These issues
  are particularly important in developing
  countries, where geothermal resources can reduce
  the economic pressures of importing fuels, and
  can provide local technical infrastructure and
  employment.
• Geothermal energy has an inherent energy storage
  capability.
• Geothermal power stations have a very low land
  area requirement.

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• Constraints to Geothermal Energy Use
• Geothermal energy produces non-condensable
  gaseous pollutants, mainly carbon dioxide,
  hydrogen sulphide, sulphur dioxide, and methane.
  The condensed geothermal fluid also contains
  dissolved silica, heavy metals, sodium and
  potassium chlorides and sometimes carbonates.
  However, modern emission controls and reinjection
  techniques have reduced these impacts to a
  minimum. Geothermal energy has a net positive
  impact on the environment because its pollution
  effects are significantly lower than those of
  conventional energy sources.
• There is the potential for geothermal production
  to cause ground subsidence. This is rare in dry
  steam resources, but possible in liquid-dominated
  fields (eg Wairakai, New Zealand). However,
  reinjection techniques can effectively remove
  this risk.
• Geothermal energy production has been associated
  with induced seismic activity. However, this is a
  debatable issue as most geothermal fields are
  located in regions that are already prone to
  earthquakes. In production plants where
  reinjection maintains reservoir pressures,
  seismic activity is not found to be much
  increased.
• Geothermal energy is not strictly renewable, and
  on a site-by-site basis is not currently being
  utilised in a sustainable manner.
• Geothermal plants produce noise pollution during
  construction (eg drilling of wells, and the
  escape of high pressure steam during testing).
  Once plants are operational, noise pollution is
  not significant.
• Geothermal energy use is constrained by energy
  policies, taxes and subsidies which encourage the
  use of fossil fuel sources. Energy prices often
  do not reflect the environmental benefits of
  geothermal energy and other renewable energy
  resources.