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Energy In a Nutshell: Geothermal Energy

By Edited Nov 13, 2013 0 0

geothermal plant

Geothermal energy is accounts for approximately 17% of the total renewable energy generation.  The main challenges with operating a geothermal plant are its low heat content and the difficulty with transport of the energy output. The source of the energy should be near the consumer, which is not always the case with ideal sites, as they are located in volcanic rock which is generally dangerous to inhabit. The main danger with geothermal drilling is seismic activity (earthquakes).

geothermal well diagram

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
10:Crystalline bedrock

Suitable reservoirs are discovered with seismic exploration, similar to hydrocarbon exploration. Acoustic shock waves are sent into the ground via vibrating plates. The reflections are recorded with an array of microphones and interpreted with a computer model. This allows geologists to get an idea of underground rock formations where suitable geothermal reservoirs may be found and the best way to drill for optimal exploitation.

Geothermal energy generation uses the earth's heat in the following ways:

  1. Direct use (heat exchange)
  2. Geothermal heat pumps
  3. Electrical power production.

For the generation of electricity, relatively wells are drilled into reservoirs where high temperatures exist. When water is inserted into the well, it heats up very quickly and turns into steam, which shoots up to the surface and is used to rotate a turbine, which in turn generates electricity. Cool water is send back down into the reservoir to replenish it, and the circle begins anew.

The advantages of geothermal energy are:

  1. Zero greenhouse gas emissions.
  2. Free energy source after the plant is built. 
  3. Small footprint of geothermal power plants, operation is relatively unproblematic (considering there is no seismic activity in the area due to the wells). 
  4. Little maintenance once the plant is built. Operation is straight forward. 
  5. Can serve as a baseload energy source, as it generates electricity relatively steady. This is very different with hydroelectric energy, or with solar energy, which can not generate electricity around the clock due to technological restrictions.

Disadvantages of geothermal energy:

  1. Suitable hot rocks must be drillable, which is often not the case. Rocks may be very hard or faulted, which is difficult to drill. 
  2. Potential seismic events during drilling and operation. This problem has shut down entire projects in the past, as for example in Basel (Switzerland). 
  3. Geothermal sites may be remote from demand.
  4. Plants cannot provide capacity for demand spikes, because they output energy relatively steadily. 
  5. Challenge of finding heat-resistant fluids for drilling and heat exchange. Temperatures in the well can be very high. 
  6. Localized depletion of reservoirs and potential escape of hazardous gases during drilling and operation.

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