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Generating Electricity

Hot water and steam from geothermal systems can be extracted via drilled geothermal wells. Electricity is generated by using the steam, or secondary fluids, to drive turbines, which in turn drive generators. Excess fluids are injected back into the subsurface reservoir to help extend the life of the system.

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Find out more about extracting the heat.

Dry Steam Power Plants
  • The first type of geothermal power plants (Italy, 1904).
  • Very effective for generating electricity.
  • Plant uses steam that is accessed by drilling directly into the underground source.
Flash Steam Power Plants
  • Hydrothermal fluid at 240 - 290°C is pushed to the surface by the high pressure in the subsurface reservoir.
  • When this very hot fluid reaches the surface, it enters the separator where the pressure drops instantaneously and most of the liquid flashes into steam.
  • The force generated by the steam is used to drive turbines and produce electricity.
  • NZ examples: Wairakei, Ohaaki, Kawerau, Mokai
Binary Power Plants
  • Wairakei Binary Plant
    Geothermal fluid from the subsurface reservoir never comes into contact with the turbine/generator units.
  • Instead, hot geothermal fluid is fed into a heat exchanger where heat is transferred to a “working liquid” with a lower boiling point than water (usually isobutane or isopentane).
  • The working liquid turns into an energised vapour and turns the turbine/generator unit, producing electricity.
  • NZ examples: Wairakei, Tauhara