Geothermal energy is far broader than volcanic power plants. It can heat a single home, serve a district network or generate steady grid electricity.
The key distinction is depth and temperature: shallow ground supports heat pumps, while power plants need much hotter resources reached by wells.
Geothermal energy has three main uses
Ground-source heat pumps move heat between a building and the shallow ground. They do not generate heat from magma and can work in many climates.
Direct-use systems deliver naturally hot water for buildings, greenhouses, industry or district heating. Geothermal power plants use high-temperature water or steam to drive generators.
These applications have different geology, drilling requirements and economics. A region unsuitable for conventional geothermal electricity may still be well suited to ground-source heat pumps.
Four facts about geothermal power
1. The first geothermal power experiment was in 1904
The first geothermal power plant was built at Larderello, Italy, in 1904, according to the U.S. Energy Information Administration. Commercial generation followed there in 1913.
2. The Geysers remains the largest geothermal complex
Calpine identifies The Geysers in Northern California as the world’s largest complex of geothermal generating facilities. Its current operating capacity is about 725 megawatts.
3. Geothermal can run around the clock
Unlike weather-dependent generation, a managed geothermal reservoir can supply heat continuously. U.S. geothermal units are commonly operated as base-load resources, although maintenance and reservoir conditions still affect output.
4. Power plants use different cycles
Dry-steam plants send reservoir steam directly to a turbine. Flash plants reduce the pressure of hot water to produce steam. Binary-cycle plants transfer heat to a secondary fluid with a lower boiling point, keeping the geothermal fluid in a closed loop.
Four facts about impact and resource limits
5. Geothermal is renewable, but reservoirs must be managed
Earth continually produces heat, but individual fields can lose pressure or cool if operators withdraw fluid faster than the reservoir is replenished. Reinjection helps maintain pressure and manage wastewater.
6. Emissions are low, not always zero
Geothermal plants do not burn fuel, but some reservoirs release carbon dioxide, hydrogen sulfide and trace gases. Emissions vary by resource and plant design. Binary plants can have very low operating emissions because the geothermal fluid remains contained.
7. Drilling dominates project risk
Developers need sufficient heat, fluid and permeability. Exploration and deep wells are expensive, and a drilled well may not deliver the expected flow or temperature.
8. Water use and induced seismicity require site-specific controls
Cooling, reinjection and reservoir stimulation can affect water demand and subsurface pressure. Enhanced geothermal systems create or reopen fractures in hot rock, so projects use monitoring and controlled injection to manage induced-seismicity risk.
Enhanced geothermal could expand the map
Conventional hydrothermal power needs naturally occurring heat, fluid and permeability. Enhanced geothermal systems are designed for hot rock that lacks enough fluid flow by creating a managed subsurface reservoir.
Closed-loop concepts circulate working fluid through sealed underground pipes instead of relying on a fracture network. Both approaches are still developing, but they could make geothermal power available beyond traditional western U.S. resources.
Current residential incentive note
For U.S. homeowners, the federal Residential Clean Energy Credit is no longer available for geothermal heat-pump expenditures made after December 31, 2025. State, local and utility incentives may still apply and should be checked before purchase.
Bottom line: geothermal energy is a firm, versatile resource, but its technology and economics depend on whether the goal is building heat, direct use or electricity generation.
Sources: U.S. Energy Information Administration geothermal overview, U.S. Department of Energy enhanced geothermal systems, Calpine Geysers information and IRS Form 5695 instructions.