Geothermal Energy

Geothermal energy is heat that originates inside the Earth, drawn from the warmth stored in rock and from the slow decay of radioactive elements in the planet's interior. Because this heat is continually supplied, geothermal is classed as a renewable energy source. It can be used both to generate electricity in power stations and to provide direct heating for homes, greenhouses and industry. Its availability is greatest in regions with volcanic activity or where hot rock lies relatively close to the surface.

For electricity generation, wells are drilled into underground reservoirs of hot water or steam. The steam, or steam flashed from hot pressurised water, drives a turbine connected to a generator. In cooler resources a binary system can be used, in which the geothermal water heats a second fluid with a lower boiling point that then drives the turbine. Spent fluids are commonly reinjected into the ground to sustain the reservoir. At smaller scale, ground-source heat pumps exploit the stable temperature of the shallow subsurface to heat buildings in winter and cool them in summer.

Geothermal sits within a broader family of renewable technologies that includes solar panels and other solar energy systems, wind turbines, hydroelectric power from dams and water wheels, and biofuels such as biodiesel. Compared with sunlight and wind, geothermal output is steady and largely independent of weather and time of day, which makes it valuable for continuous baseload supply. Its main limitations are the cost of drilling and the fact that the highest-grade resources are concentrated in particular geological settings.

Frequently asked questions

Where does geothermal heat come from?

It comes from heat retained inside the Earth and from the decay of radioactive elements in its interior. This heat warms underground rock and water, which can be tapped at the surface.

Is geothermal energy renewable?

Yes. The Earth continually supplies heat, so a well-managed geothermal reservoir can provide energy over the long term, especially when spent fluids are reinjected to maintain it.

How is geothermal different from solar or wind power?

Solar and wind output varies with weather and time of day, while geothermal heat is available continuously. This makes geothermal well suited to steady, around-the-clock electricity and heating.