Geothermal energy is power extracted from heat stored inside the Earth. The heat is generated from radioactive decay, volcanic activity, core convection and solar energy absorbed at the Earth’s surface. Geothermal power plants pump water down a borehole into hotspots a few kilometres beneath the Earth, then force it out of a second borehole into a steam turbine to produce electricity. Geothermal power plants
- Tower The central tower acts as a fl ue to draw hot air through the turbines, as well as housing the plant’s machinery and generator.
- Thermal storage During the day the Sun’s rays heat air under the collector membrane to high levels. At night heat radiated from the ground is better contained under the collector.
- Collector membrane This is made from clear plastic and while allowing a large proportion of the Sun’s rays to pass through it without refl ection, almost completely traps the heated air beneath it, adding an accumulative effect.
- Turbines The updraft tower is fi tted with multiple turbines at its base that suck the hot air inwards from under the collector membrane to generate electricity.
A diagram of a geothermal power plant showing the drilling of a borehole to a depth of 5km. At this depth, a layer of water has formed from rainwater draining through the ground (blue arrows). The water is heated by magma, and the borehole enables the energy of the heated water to be extracted.
A. Injection well
B. Hot water to district heating
C. Porous sediments
D. Observation well
E. Crystalline bedrock