Beneath the Earth’s surface lies an enormous reservoir of thermal energy — heat generated by radioactive decay in the planet’s core and mantle. Geothermal energy harnesses this heat for electricity generation, direct heating, and industrial processes. As the world transitions away from fossil fuels, geothermal energy offers a unique advantage over other renewables: it provides constant, baseload power regardless of weather conditions or time of day.
How Geothermal Energy Works
The Earth’s interior temperature increases with depth at an average rate of about 25 to 30 degrees Celsius per kilometre in most regions. In geologically active areas — near tectonic plate boundaries, volcanic zones, and hot spots — this thermal gradient is much steeper, with temperatures exceeding 200 degrees Celsius at accessible depths of just a few kilometres.
Conventional geothermal power plants tap naturally occurring reservoirs of hot water and steam. Flash steam plants, the most common type, draw hot water under pressure from underground and allow it to “flash” into steam as the pressure drops, driving turbines connected to generators. Binary cycle plants use hot geothermal fluids to heat a secondary working fluid with a lower boiling point, enabling power generation from lower-temperature resources. Dry steam plants, the oldest design, directly use underground steam to drive turbines.
Enhanced Geothermal Systems
The most exciting development in geothermal energy is Enhanced Geothermal Systems (EGS), which could make geothermal power available virtually anywhere on Earth. EGS involves drilling deep wells into hot dry rock, injecting water under pressure to create fractures in the rock, and circulating water through these fractures to extract heat. The heated water returns to the surface to generate electricity before being recirculated underground.
In 2023, the startup Fervo Energy demonstrated the first commercial-scale EGS project in Nevada, achieving flow rates and temperatures sufficient for significant power generation. The U.S. Department of Energy estimates that EGS could provide over 100 gigawatts of generating capacity in the United States alone — enough to power tens of millions of homes — making it comparable in potential to wind and solar energy combined.
Global Geothermal Leaders
Iceland leads the world in geothermal energy utilisation, generating about 25 percent of its electricity and heating nearly 90 percent of its homes from geothermal sources. Kenya generates roughly 45 percent of its electricity from geothermal plants in the Great Rift Valley. Other major geothermal producers include the United States (the world’s largest by total capacity), Indonesia, the Philippines, and New Zealand.
Canada, despite its vast geological resources, has only recently begun developing geothermal energy. The Canadian Geothermal Energy Association has identified promising resources in British Columbia, Alberta, and the Northwest Territories, and regulatory frameworks are evolving to support development.
Advantages and Challenges
Geothermal energy produces minimal greenhouse gas emissions — roughly 5 percent of what a coal plant emits per unit of electricity. It requires very little land compared to solar or wind farms, and geothermal plants operate continuously with capacity factors exceeding 90 percent, compared to about 25-35 percent for wind and solar.
Challenges include high upfront drilling costs and the geological risk that a given site may not yield sufficient heat or fluid flow. Induced seismicity — small earthquakes triggered by fluid injection — requires careful site selection and management. However, advances in drilling technology borrowed from the oil and gas industry, combined with improved geological characterisation using machine learning, are steadily reducing these risks and costs, positioning geothermal energy as a critical component of a clean energy future.
