Geothermal Power Plants
 

               The Mammoth Pacific Binary geothermal power plant, Casa Diablo

                          

           

                         Svartsengi geothermal power plant, Iceland

 

       Types of geothermal power plants:

  • Dry Steam

  • Flash Steam

  • Binary Cycle

Dry steam power plants systems were the first type of geothermal power generation plants built. They use the steam coming form the wells, and route it through turbine/generator units to produce electricity. Flash steam plants are currently the most common type of geothermal power generation plants. They use water at temperatures greater than 182°C which is pumped under high pressure to the generation equipment at the surface. Binary cycle geothermal power generation plants differ from Dry Steam and Flash Steam systems in that the water or steam from the geothermal reservoir never comes in contact with the turbine/generator units. Geothermal plants require hot rock near to the surface and which is sufficiently fractured to allow the heated water to pass.

 

Advantages

  • Hydrothermal electric power plants are reliable - they are online (standby efficiency) about 90%-97% of the time (compared with to 75% for coal plants and 65% for nuclear reactors)

  • New facilities emit 0.1 kg of carbon per megawatt-hour of electricity generated, compared with 185 kg of carbon per megawatt-hour for a coal-fired facility.

  • They are flexible - geothermal systems can be installed modularly, increasing power levels to fit demand

  •  Construction of smaller geothermal plants (5-10MW) can take only 6 months; larger plants (>250MW) might take about 2 years.

  • Geothermal power plants use only a fraction of land in comparison to conventional power plants and the land can be used at the same time for other purposes (i.e. agriculture)

  • Renewable if extractions does not exceed natural replenishing

  • CO2 emission of geothermal plants is 1000-2000 times less than gas, coal or oil-fired plants.

  • Binary plants do not produce any air or liquid emissions & are considered to be a dominating technology in the near future.

  • Do not require transportation of fuels

  • Some geothermal plants produce solid materials, which can be sold (e.g. zinc, silica, sulfur), making the resource more valuable and environmentally friendly.

  • Salts and minerals are reinjected with water back into the reservoir below groundwater aquifers, which recycles the geothermal water.

 

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Disadvantages

  • Not all locations are suitable (geological suitability and distance to the consumers of geothermal energy).
  • Can release sulphur dioxide and hydrogen sulphide emissions from dissolved gases in fluids when on the surface.
  • High initial costs (drilling, plant design and pipeline construction).
  • Surface disturbance
  • Spent water is polluted with heavy metals (which can be reinjected back where it came from)
  • The geothermal capacity can run out or diminish especially if it is managed improperly, at which point power plant needs to be moved.