How do geothermal power plants use Earth's heat for electricity?

Geothermal power plants generate electricity by harnessing heat from the Earth's interior.

Geothermal power plants utilise the Earth's natural heat in a few different ways, but all types of plants start with a well that is drilled deep into the Earth. The depth of these wells can range from a few hundred to several thousand metres, depending on the location and the specific technology being used. The purpose of these wells is to reach areas where the Earth's heat is intense enough to produce steam.

The most common type of geothermal power plant, known as a dry steam power plant, directly uses the steam from the Earth's interior to turn a turbine. The steam is brought up through the well, and directed to a turbine generator. As the steam rushes past the turbine blades, it causes them to spin. This spinning motion is then converted into electrical energy through an electromagnetic process in the generator.

Another type of geothermal power plant, called a flash steam power plant, uses water that is hotter than 182 degrees Celsius. When this high-pressure hot water is drawn up to the cooler surface, it rapidly converts, or 'flashes', into steam. This steam is then used to turn the turbine and generate electricity. Any leftover water and condensed steam are injected back into the reservoir, making this a sustainable and renewable energy source.

Binary cycle power plants are the third type of geothermal power plant. These plants use water at lower temperatures of about 107-182 degrees Celsius. The hot water is passed through a heat exchanger, transferring its heat to a secondary fluid (a binary fluid) which boils at a lower temperature than water. This secondary fluid turns into steam which, like in the other types of plants, drives a turbine connected to a generator.

In all these types of geothermal power plants, the process is continuous as long as the heat supply from the Earth's interior remains constant. This makes geothermal power a reliable and sustainable source of energy. However, the efficiency of geothermal power plants is dependent on the temperature of the geothermal resource; the hotter it is, the more efficient the power generation.