Geothermal energy is a renewable resource that draws on the Earth's internal heat to provide both electricity and direct heating, with a long history of human use and a contemporary role that continues to expand.
Geothermal energy refers to thermal energy extracted from the Earth's crust, originating from both the planet's formation and ongoing radioactive decay. It can be accessed through naturally occurring hot springs, engineered reservoirs, or shallow ground heat for heating and cooking.
Modern geothermal systems tap underground reservoirs of hot water or steam through wells, bringing heat to the surface for electricity generation, direct heating, or geothermal heat pumps.
People have used geothermal heat for thousands of years. Hot springs were used for bathing as early as Paleolithic times. The Romans used geothermal waters for public baths and underfloor heating. The oldest geothermal district heating system began operating in Chaudes-Aigues, France, in the 15th century. Industrial use began in the 19th century, when geyser steam was used to extract boric acid from volcanic mud.
Geothermal power plants convert underground heat into electricity. They operate most effectively where hot water or steam is located close to the surface, often near tectonic plate boundaries. Geothermal plants produce constant, weather-independent power, and costs have fallen significantly since the 1980s. Internationally, Indonesia and Kenya are major producers, with Kenya generating 45% of its electricity from geothermal sources.
Geothermal heating takes two main forms: direct use and district heating, and geothermal heat pumps (GHPs).
Hot water from shallow reservoirs is piped directly into buildings or used for industrial processes such as food drying and greenhouse heating. Reykjavik, Iceland, is a leading example of city-scale geothermal district heating.
Geothermal heat pumps use the stable temperature of shallow ground to heat and cool buildings efficiently. They work by transferring heat between the ground and indoor spaces.
Geothermal systems include direct use systems (which tap naturally warm water near the surface), geothermal power plants (which require high-temperature water or steam), and geothermal heat pumps (which use shallow ground temperatures for heating and cooling).
Today, geothermal energy supports electricity generation, residential and commercial heating and cooling, industrial processes (drying, pasteurizing, mining), agricultural applications (greenhouses, aquaculture), and spas and recreational uses. Worldwide, an additional 28 GW of geothermal heat is used for non-electric applications.
Geothermal energy is considered renewable because the Earth continuously produces internal heat. Resources are vast - more than sufficient to meet global energy needs if accessed effectively.
Environmental impacts include low emissions (geothermal plants emit far less carbon dioxide than fossil fuels), a small land footprint (facilities require less space than solar or wind installations), water use (some systems require water for reinjection or cooling), induced seismicity (enhanced geothermal systems can trigger small earthquakes due to fluid injection), and localized impacts (potential release of trace gases or minerals from underground reservoirs). Overall, geothermal energy is among the cleanest and most reliable renewable energy sources, with manageable environmental impacts when properly regulated.
Recommended Resources
Currently a business unit of Constellation Energy Corporation, Calpine is presented as America's premier competitive power company. Its website emphasizes the company's role in generating and supplying electricity across North America and its focus on clean energy technologies. Operating more than 78 facilities across North America, and operates geothermal baseload at The Geysers, highlighting carbon capture and decarbonization projects and other initiatives to support a cleaner energy future.
https://www.calpine.com/
Based in Houston, Texas, Fervo Energy is a geothermal company that generates electricity through enhanced geothermal systems (EGS). Founded in 2017, its first commercial pilot geothermal plant, Project Red, was launched in 2023, and it later developed Cape Station, its first multi-phased Greenfield geothermal development. Its technology, operations, team, and news articles are published on the site, along with career opportunities, social media, and contact details.
https://fervoenergy.com/
Incorporated in 2014, and headquartered in Oklahoma City, Oklahoma, GreenFire Energy is a tech-enabled geothermal developer that builds and deploys Advanced Geothermal Systems (AGS), including a closed-loop "GreenLoop" technology to deliver reliable, behind-the-meter baseload power and to revitalize underutilized geothermal assets. The company develops purpose-built geothermal projects that combine AGS, EGS, and conventional approaches to match technology to geology.
https://www.greenfireenergy.com/
International Energy Agency Geothermal
Operating through the International Energy Agency Technology Collaboration Programme, the IEA Geothermal program fosters international collaboration among nations, industries, and organizations to promote research, development, commercialization, and deployment of geothermal energy resources. Often referenced as IEA-GIA or IEA Geothermal implementing activities, its strategic plan, delegates, members, activities, reports, case studies, and events are featured.
https://www.iea-gia.org/
International Geothermal Association
Founded in 1988 in Auckland, New Zealand, the IGA is a non-profit, non-political, non-governmental association representing the geothermal energy sector globally. Headquartered in The Hague, Netherlands, with members in more than 88 countries, its stated mission is to advocate for geothermal energy as a key contributor to the global energy transition and climate change mitigation. The IGA has consultative status with the United Nations and special observer status with the Green Climate Fund.
https://worldgeothermal.org/
Headquartered in Reno, Nevada, Ormat Technologies was established in 1965. The company delivers renewable power and energy to customers around the world, including what is described as clean, reliable energy solutions provided from geothermal power, recovered energy, as well as energy storage solutions. The company designs, builds, and supplies power generating equipment for its customer's geothermal and recovered energy power plants in more than 30 countries.
https://www.ormat.com/en/
Established in 2003, Star Energy Geothermal is Indonesia's largest geothermal energy producer and a leading clean energy company, operating major fields at Salak, Darajat, Wayang Windu, Hamiding, and Sekincau, which are featured. The company emphasizes reservoir management, drilling, and power generation to support Indonesia's energy transition. Its locations, contact details, board of directors, awards and accolades, reports, and policies are featured on its website.
https://www.starenergygeothermal.co.id/
Through its website and a weekly newsletter, Think GeoEnergy seeks to be an information services provider for the global geothermal energy sector and the market it serves. It delivers business-to-business news with a focus on development, technology, finance, and related topics, paired with market analysis and events. Founded in 2008, it also takes on new topics, such as deep geothermal heat exchange systems, storage, and mineral extraction from geothermal brine.
https://www.thinkgeoenergy.com/
