Geothermal Electricity

Medium- and high-energy geothermal power harnesses extremely hot water and steam from the earth’s subsurface for use in specific power plants to generate electricity. These techniques also have industrial applications.

How does geothermal electricity work?
© Keblow

Medium-energy Geothermal Power Plants

When geothermal water is at temperatures of 90-150°C,
it can be used in liquid form to produce electricity. This is called medium-energy geothermal power. This technique involves power plants that use wells drilled in the ground to harness underground water.

Geothermal power plants use wells to harness hot water from the subsurface.

Thus, medium-energy geothermal power plants are built near aquifers located at depths of 2000-4000 m. In volcanic areas, where the subsurface holds more heat, water used by the power plants is sometimes found at depths of less than 1,000 m.

These plants use pressurized water (to stop it from boiling) that circulates in a system called a heat exchanger. This device contains pipes filled with geothermal water which come into contact with pipes filled with a specific liquid (generally a hydrocarbon). When it comes into contact with the water-filled pipes, the liquid heats up, boils, and vaporizes. The gas obtained drives a turbine that produces electricity. The gas is then cooled down again and liquefied before being reused in another production cycle.

High-Energy Geothermal Power in Volcanic Areas

If the temperature of the geothermal water exceeds 150°C, it can be used directly as steam to drive turbines to generate electricity in a process called high-energy geothermal power. This principle was used as long ago as 1913 in the very first geothermal power plant in history, in Larderello, Italy.

High-energy power plants harness the steam in water tables in volcanic regions, at depths of 1500-3000 m. Under certain pressure and temperature conditions, the steam harnessed in the subsurface is wet, i.e. it contains a fraction of water in liquid form. In this case, the liquid water is isolated from the dry steam using a device called a separator. The dry steam is sent to the turbine while the liquid water is vaporized by reducing its pressure before being sent to the turbine.

Medium- or high-energy geothermal power is only used to produce electricity.

False. Medium- or high-energy geothermal power is used in a wide variety of applications. For example, in the industrial sector, geothermal water and steam can be used to wash and dry wool, or to manufacture pulp.