Geothermal Energy

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Geothermal Energy
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Introduction

• The center of the Earth is very hot,
  approximately 5000 K. 1
• More than 95 of the Earths volume is warmer
  than 1000 K 4
• The major part of the heat originates from
  radioactive decay (80 ), minor contributions
  come from tidal forces, and heat from the
  original formation of the Earth. 2
• The continuous heat flow from the interior of the
  earth is 42 TW. 1

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Introduction

• This leads to an average heat flux of 0.1 MW/km2.
• Through the crust the temperature gradient is 25
  K/km. 3
• Near tectonic plate boundaries and other hotspots
  these values are much higher. 3

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Current use

• In 2005 more than 9 GW electricity was produced
  by geothermal power plants worldwide. 5
• Additionally more than 28 GW were used for direct
  heating. 5
• Geothermal energy provided 0.3 of the worldwide
  energy consumption. 2
• Almost all existing geothermal power plants are
  located in areas, where the geothermal activity
  is apparent. 1

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Wells

• The most important parts of a geothermal power
  plant is the wells.
• The wells are drilled into a natural collection
  of hot water, called a geothermal reservoir.
• Usually the wells are not deeper than 3000 m, but
  the limit for today's drilling technology is
  about 10000 m. 6
• A geothermal reservoir can also be created by
  injecting water into the rock, this method is
  called hot dry rock or enhanced geothermal
  systems. 6

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Electricity production

• Converting geothermal energy into electricity is
  relatively simple.
• Hot water/steam, with a temperature of 150 200
  C, are led through a turbine, and then injected
  back into the rock. 6

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Electricity production

• Binary geothermal plants can be used to produce
  electricity, when the water temperature is lower
  (100 150 C). 1
• The binary fluid has to vaporize at temperatures
  below 100 C. 1

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Heating

• Geothermal energy has been used for heating since
  ancient Roman times.
• Dont require very hot water. 3
• A effective way to use geothermal energy. 3

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Heating

• Geothermal energy can be used to heat a single
  house or an entire city. 3

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Advantages

• Geothermal energy is reliable, it will be
  available 24 hours every day. 1
• Geothermal energy is renewable, as long as water
  is injected into the reservoir and the amount of
  water extracted is in balance with the capacity
  of the reservoir. 1
• It produces very little pollution. 1
• Highly scalable. 3

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Disadvantages

• Drilling is expensive. 3
• The success of a drilling attempt cant be
  guaranteed. 3
• If water is injected into the Earth it can
  trigger earthquakes. 3

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References

• 1 A guide to geothermal energy and the
  environment, Alyssa Kagel, Diana Bates, Karl
  Gawell, Geothermal energy association,
  http//www.geo-energy.org/Publications/reports/Gui
  de20to20Geothermal20Energy20and20Environment.
  pdf
• 2 Wikipedia Geothermal gradient,
  http//en.wikipedia.org/wiki/Geothermal_gradient
• 3 Wikipedia Geothermal power,
  http//en.wikipedia.org/wiki/Geothermal_power
• 4 Earth's Interior, University of Nevada, Reno,
  http//www.seismo.unr.edu/ftp/pub/louie/class/100/
  interior.html
• 5 Characteristics, development and utilization
  of geothermal resources, John W. Lund, Geo-Heat
  Center, Oregon Institute of Technology,
  http//geoheat.oit.edu/pdf/tp126.pdf
• 6 The future of geothermal energy,
  Massachusetts institute of technology,
  http//geothermal.inel.gov/publications/future_of_
  geothermal_energy.pdf
• 7 Introduction to geothermal energy slide show,
  Geothermal education office, http//www.geothermal
  .marin.org/GEOpresentation/index.htm