Geothermal Basics

Geothermal Energy

Geothermal energy is heat energy from the earth—geo (earth) + thermal (heat).

Geothermal resources are reservoirs of hot water that exist or are human-made at varying temperatures and depths below the earth's surface. Wells ranging from a few feet to several miles deep can be drilled into underground reservoirs to tap steam and very hot water that can be brought to the surface for use in a variety of applications, including: 

Electricity Generation

Deep underground, the presence of hot rocks, fluid, and permeability (the ability for that fluid to move among the rocks) offer conditions from which electricity can be generated. Using natural or human-made permeability and fractures, the fluid flows through the hot rocks, absorbing heat from the rocks that can be drawn up through wells to Earth’s surface. That heat energy is then converted to steam, which drives turbines that produce electricity. Learn more about geothermal electricity generation.

Heating and Cooling 

Geothermal resources such as naturally occurring underground reservoirs of hot water or the stable temperature of the subsurface can be used to heat and cool buildings. Geothermal heat pumps provide heating and cooling using the ground as a heat sink, absorbing excess heat when the aboveground temperatures are warmer, and as a heat source when aboveground temperatures are cooler. District heating and cooling systems use one or more types of geothermal systems, such as a  series of geothermal heat pumps, in order to heat and cool groups of buildings, campuses, and even entire communities. Learn more about geothermal heating and cooling. 

Direct Use

Geothermal direct use applications use wells—usually deeper than those for heat pumps—to draw hot water from the subsurface to directly provide hot water to buildings, space heating, or heat for industrial processes ranging from fish farming and greenhouses to drying pulp, paper, lumber, and other materials. Learn more about direct use.

Benefits of Geothermal Energy

Firm and Flexible—Geothermal power plants produce electricity consistently and can run essentially 24 hours per day/7 days per week, regardless of weather conditions. They can also ramp generation up or down to respond to changes in electricity demand.

Domestic—U.S. geothermal resources can be harnessed for power production and heating and cooling without importing fuel.

Innovative—Modern geothermal power plants release no greenhouse gasses and have a life cycle impact four times lower than solar PV, and six to 20 times lower than natural gas. Geothermal power plants consume less water on average over the lifetime energy output than most conventional electricity-generation technologies (source). 

Small footprint—Geothermal power plants and geothermal heat pumps are compact. Geothermal power plants use less land per gigawatt-hour (404 m²) than comparable-capacity coal (3,642 m²), wind (1,335 m²), and solar photovoltaic (PV) power stations (3,237 m²) (source). GHPs can be retrofitted or integrated in new buildings.

Sustained—The heat flowing from Earth’s interior is continually replenished by the decay of naturally occurring radioactive elements and will remain available for billions of years.

U.S. Geothermal Growth Potential

The 2019 GeoVision analysis indicated potential for up to 60 gigawatts of electricity-generating capacity, more than 17,000 district heating systems, and up to 28 million geothermal heat pumps by 2050. 

In 2022, the Enhanced Geothermal Shot™ analysis confirmed the potential for even more geothermal electricity-generating capacity—90 gigawatts by 2050—if we can achieve aggressive cost reductions in enhanced geothermal systems. The Next-Generation Geothermal Power report even identified the potential for up to 300 GW of next-generation geothermal electricity generation, depending on the development of storage capabilities and other emerging technologies. For heating and cooling, the Next-Generation Heating and Cooling Liftoff Report notes the potential for geothermal heat pumps to support the equivalent of 36 million homes by 2050.  

U.S. Department of Energy Geothermal Technologies Office

The U.S. Department of Energy (DOE) Geothermal Technologies Office (GTO) focuses on realizing the potential to generate electricity and produce heating and cooling for U.S. homes from domestic geothermal resources. To do so, GTO works in partnership with industry, academia, DOE's national laboratories, and others on research, development, and demonstration activities focused on these areas:

• Enhanced Geothermal Systems (EGS) – Advancing the commercial viability of EGS (human-made geothermal energy).
• Hydrothermal Resources – Advancing technologies to expand electricity generation using naturally occurring geothermal resources and value-added opportunities like lithium extraction. 
• Low-Temperature and Coproduced Resources – Improving the efficiency and expanding the utility of low-temperature (<300° F) geothermal systems such as geothermal heat pumps and district heating and cooling systems. 
• Data, Modeling, and Analysis – Addressing nontechnical barriers to geothermal deployment through environmental and resource assessments, data stewardship, and analytical tools.

Learn more about GTO's work and funding opportunities.