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Heat from the Earth’s Center
Electricity Production
Dry-steam power plants
Flashed-steam power plants
Binary-cycle power plants
Direct Use Applications
Geothermal Heat Pumps
Air Quality
Water Quality
Landscape Impacts and Land Use
Noise Pollution
Impact on Wildlife and Vegetation
A geothermal resource can be simply defined as a
reservoir inside the Earth from which heat can be
extracted and utilized for generating electric power or any
other suitable industrial, agricultural or domestic
application in the near future. It is considered a renewable
energy resource. The heat continuously flowing from the
earth’s interior is estimated to be equivalent to 42 million
megawatts . One megawatt is equivalent to 1 million
watts, and can meet the power needs of about 1,000

Source  of this Energy—the earth’s internal heat. The
Earth’s temperature increases with depth, with the
temperature at the center reaching more than 4200 °C
(7600 °F).
A portion of this heat is a relic of the planet’s formation
about 4.5 billion years ago, and a portion is generated by
the continuing decay of radioactive isotopes.
 Heat naturally moves from hotter to cooler regions, so
Earth’s heat flows from its interior toward the surface.

2.1 Heat from the Earth’s Center
 • Earth's core maintains temperatures in excess of
 – Heat radial radioactive decay of elements
 • Heat energy continuously flows from hot core
 – Conductive heat flow
 – Convective flows of molten mantle beneath the crust.
 • Mean heat flux at earth's surface
 – 16 kilowatts of heat energy per square kilometer
 – Dissipates to the atmosphere and space.
 – Tends to be strongest along tectonic plate boundaries
 • Volcanic activity transports hot material to near the
 – Most is left at depths of 5-20 km beneath the surface,
 • Hydrological convection forms high temperature
  -Geothermal systems at shallow depths of 500-3000m.

There are three primary ways we can use geothermal energy: for
electricity production, for direct-use applications, and for heating
and cooling buildings with geothermal heat pumps.

3.1 Electricity Production
3.1.1 Dry-steam power plants
3.1.2 Flashed-steam power plants
3.1.3 Binary-cycle power plants

3.1.1 Dry-steam POWER plants
  Dry steam power plants draw heat from
  underground reservoirs of steam. The steam is
  piped directly from wells to the power plant, where
  it enters a turbine. The steam turns the turbine,
  which turns a generator. The steam is then
  condensed and injected back into the reservoir via
  another well. The Geysers in northern California,
  the world’s largest single source of geothermal
  power, uses dry steam.

Dry-steam power plants
3.1.2 Flashed-steam power plants

Flashed-steam power plants tap into reservoirs of water
with temperatures greater than 360°F (182°C). This very
hot water flows up through wells under its own pressure.
As it flows to the surface, the fluid pressure decreases and
some of the hot water boils or ―flashes‖ into steam. The
steam is then separated from the water and used to power
a turbine/generator unit. The remaining water and
condensed steam are injected through a well back into the

Flashed-steam power plants
       3.1.3 Binary-cycle power plants
Binary-cycle power plants operate with water at lower
temperatures of about 225° to 360°F (107° to 182°C).
These plants use heat from the geothermal water to boil a
working fluid, usually an organic compound with a lower
boiling point. The working fluid is vaporized in a heat
exchanger and the vapor turns a turbine. The water is
then injected back into the ground to be reheated. The
water and the working fluid are confined in separate
closed loops during the process, so there are little or no
air missions.

Binary-cycle power plants
          Direct Use Applications
• Geothermal heat is used directly rather than for power
• Extract heat from low temperature geothermal resources
–       < 150 oC or 300 oF.
• Applications sited near source (<10 km)

Today,  most geothermal direct-use applications circulate
these fluids through closed-loop, emissions-free systems.

The  carbon dioxide found in geothermal fluids could prove
beneficial to direct-use greenhouse applications. Carbon
dioxide is a very effective growth stimulant for plants.
Studies have shown that an increase in carbon dioxide from
a normal level of 300 ppm to approximately 1,000 ppm can
raise crop yields up to 15 percent.
 3.3 Geothermal Heat Pumps
              The use of geothermal energy through ground-
coupled heat pump technology has almost no impact on the
environment and has a beneficial effect in reducing the
demand for electricity
Because of this constant temperature, the energy
efficiency of geothermal heat pumps is about 30% better
than that of air-coupled heat pumps and 50% better than
electric-resistance heating.
The need for electrical generation capacity at the central
power station is reduced by 2 to 5 kW for each residential
installation and by about 20 kW for average commercial
installations. Thus, for each 1000 homes with geothermal
heat pumps, the utility can avoid the installation of 2 to 5
MW of generating capacity.

  4. Environmental Impact
Because   geothermal power plants do not burn fuel like fossil
fuel plants, they release virtually no air emissions. A case
study of a coal plant Updated emits 24 times more carbon
dioxide, 10,837 times more sulfur dioxide, and 3,865 times
more nitrous oxides per megawatt hour than a geothermal
steam plant.
4.1.Air Quality
4.2. Water Quality
4.3. Landscape Impacts and Land Use
4.4. Noise Pollution
4.5. Impact on Wildlife and Vegetation

                  4.1.Air Quality
When   a steam phase separates from boiling water, carbon
dioxide is the dominant (over 90% by weight) non condensible
Most hydrothermal systems have very low oxygen activity,
and these systems commonly contain the reduced species
H2S, NH3, and CH4, in the steam phase.
Binary geothermal power plants do not allow a steam phase
to separate, so carbon dioxide and the other gases remain in
solution and are reinjected into the reservoir, resulting in no
atmospheric emissions.
 For each megawatt-hour of electricity produced in 1991, the
average emission of carbon dioxide by plant type in the U.S.
was: 990 kg from coal, 839 kg from petroleum, 540 kg from
natural gas, and 0.48 kg from geothermal flashed-steam.

Nitrogen Oxide Comparison

Sulphur Dioxide Comparison

Air Emissions Summary

      4.2. Water Quality
Systems  in sedimentary rocks seem to have higher
concentrations than those in volcanic or granitic rocks
 Temperatures up to 380°C have been recorded in
geothermal reservoirs in the U.S and many chemical
species have a significant solubility at high temperature.

4.3. Landscape Impacts and Land Use

Geothermal   power plants require relatively little land.
Geothermal installations don’t require damming of rivers
or harvesting of forests, and there are no mineshafts,
tunnels, open pits, waste heaps or oil spills.
 An entire geothermal field uses only1–8 acres per MW
versus 5–10 acres per MW for nuclear plants and 19 acres
per MW for coal plants

4.4. Noise Pollution
Normal geothermal power plant operation typically produces less noise
than the equivalent produced ,near leaves rustling from breeze,
according to common sound level standards, and thus is not considered
an issue of concern

4.5. Impact on Wildlife and
 Before geothermal construction can begin, an environmental review
may be required to categorize potential effects upon plants and animals.
 Power plants are designed to minimize the potential effect upon
wildlife and vegetation, and they are constructed in accordance with a
host of state and federal regulations that protect areas set for

5. Economic Consideration
Cost depends upon,

• Temperature and depth of resource
• Type of resource (steam, liquid, mix)
• Available volume of resource
• Permeability of rock formations
• Size and technology of plant
• Infrastructure (roads, transmission lines)
• Costs highly variable by site
• High exploration costs
• High initial capital, low operating costs
– Fuel is ―free‖
• Significant exploration & operating risk
– Adds to overall capital costs
   6. World Geothermal Production
The  source of geothermal energy, the Earth’s heat, is
available 24 hours a day, 365 days a year.
For United States In 2003, geothermal was the third largest
source of renewable energy. Geothermal provided 0.3 percent
of total national energy production, and accounted for 5
percent of total annual renewable energy production
California has an installed capacity of 2478MW of
geothermal power plants.
Newcomers in the electric power sector are Ethiopia (1998),
Guatemala (1998) and Austria (2001).
 In total, including Indonesia, Philippines, Italy, New
Zealand, Iceland, Mexico, Costa Rica, El Salvador, 22 nations
are generating geothermal electricity, in amounts sufficient to
supply 15 million houses.

United States Renewable
Electricity Use, 2003
California renewable energy
          use,2003            31
              7. CONCLUSION
Abundant geothermal resources throughout the nation can provide
an environmentally friendly source of energy. Data compiled from
a variety of sources point to geothermal energy as an
environmental option for new power generation that is far better
than other energy sources such as fossil fuels. In addition,
geothermal remains as environmentally friendly as most other
renewable sources, while simultaneously offering reliability and a
source of baseload power that is unique among most other
renewable options available. The Department of Energy, along
with several scientific laboratories, conducts research on a regular
basis to improve the already minimal environmental impacts of
geothermal energy and to decrease the associated costs. While
currently used at only a fraction of its potential, geothermal
energy can substantially contribute to the energy needs of the
twenty-first century. With continued technological development,
geothermal can be expanded from the western states to all of the
United States, and the already negligible environmental
geothermal impacts can be reduced to nearly zero. Geothermal
energy can provide the clean, reliable, and plentiful renewable
energy resource for our nation and for the world.

             8. REFERENCES
•By  Alyssa Kagel, Diana Bates, & Karl Gawell ,A Guide to
Geothermal Energy and the Environment Geothermal Energy
Association 209 Pennsylvania Avenue SE, Washington, D.C.
•By Harsh Gupta $ Sukanta Roy , Text Book, Geothermal
Energy An Alternate Resourcr For The 21st Century
•F. S. Sterret Boca Raton, Alternative Fuels and the
Environment, : CRC Press, 1995.
•Bloomfield, K.; Moore, J.; Neilson, Jr., R. ―Geothermal Energy
Reduces Greenhouse Gases,‖ Geothermal Resource Council
Bulletin, March/April 2003, p. 77-79.
•―Environmental Impacts of Geothermal Energy,‖ U.S.
Department of Energy Geothermal Technologies Program Web
(26 May 2004).
• By Masashi Shibaki With Fredric Beck, Geothermal Energy for
Electric Power A REPP Issue Brief , Executive Editor
December 2003