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Geothermal Power Plants

Large metal tubes commonly found on geothermal power plants.

Geothermal power plants are used in various parts of the world in order to provide a sustainable and environmentally friendly source of electricity. These power stations rely on the geothermal activity that takes place deep down beneath our feet. In this article we take a look at geothermal power facilities and how they are able to produce electricity from geothermal energy.

The Different Types of Geothermal Power Plants

There are three main types of geothermal power plant in operation today:

  • Dry Steam – This is the simplest and oldest type of geothermal power station.
  • Flash Steam – This is the most common type of geothermal power station in operation today.
  • Binary Cycle – This is the latest innovation in geothermal power plant design.

How Do They Work?

Geothermal power plants work in much the same way as other thermal power stations by utilising a turbine that is driven by steam. The exact process depends on the type of geothermal power plant as all three designs operate in slightly different ways but what all three do have in common is an injection well and a production well.

The following sections detail how each type of geothermal power station design is able to produce electricity.

Dry Steam Geothermal Power Plants

The dry steam power plant design makes direct use of geothermal steam at 150°C or more. Cold water is pumped down the injection well deep into the earth. As the water meets hot rocks it turns to steam which is then extracted through the production well. This steam will then be fed directly to a steam turbine which will rotate a generator to produce electricity. The main problem with this design is that you must not pump too much cold water into the earth as this could cool the rocks too much resulting in the geothermal hot spot becoming depleted.

Flash Steam Geothermal Power Plants

The flash steam power plant design works in a similar way to that of a dry steam power plant only steam isn’t extracted through the production well. Instead, high pressure water that has been superheated to at least 180°C is extracted from deep within the earth through the production well. As the liquid flows toward the surface, the pressure decreases which causes some of the fluid in the well to separate or “flash” into steam. Once at the surface, the liquid is fed through a variety of systems that further reduce its pressure. This allows more of the fluid to “flash” into high-pressure steam which can then be fed into the steam turbine to produce electricity.

In modern flash steam power plants, any remaining liquid can be returned to the reservoir deep beneath the earth’s surface through the injection well. In addition, the steam that is used by the turbine can be passed through a condenser turning it back to a liquid which can then also be returned to the reservoir. All this careful management helps to reduce the possibility that a geothermal hotspot becomes depleted.

Binary Cycle Geothermal Power Plants

The binary cycle power plant design works in a similar way to that of the flash steam power plant although it can make use of water with a temperature as low as 57°C. It does this by passing the water by a secondary fluid that has a much lower boiling point than water. This process causes the secondary fluid to flash into steam and the steam is then fed to the turbine to produce electricity.