Geothermal energy is classified as renewable. The heat beneath Earth’s surface is continuously replenished by the radioactive decay of elements like uranium, potassium, and thorium, and it will remain available for billions of years. Every major energy agency, including the U.S. Department of Energy and the EPA, categorizes geothermal alongside solar and wind as a renewable resource. But the full picture has an important nuance: while the planet’s heat supply is essentially infinite, individual geothermal reservoirs can be depleted if they’re managed poorly.
Where Earth’s Heat Comes From
Earth’s interior runs on two fuel sources. Most of the heat is left over from the planet’s formation roughly 4.5 billion years ago, when gravitational compression and colliding material generated enormous temperatures. The second source is ongoing: radioactive elements in the crust and mantle continuously break down and release energy, adding heat and slowing the planet’s cooling. This process has no foreseeable end point.
To put the scale in perspective, Earth’s interior radiates about 0.05 watts per square meter to the surface. That sounds tiny next to the 341 watts per square meter delivered by the sun, but it’s spread across the entire planet and never stops. There’s no night cycle, no cloudy day, no calm wind. The heat is always there, which is exactly why geothermal plants can run around the clock.
Why It Outperforms Solar and Wind on Reliability
Geothermal power plants operate at capacity factors between 90% and 95%, meaning they produce electricity at or near their maximum output almost all the time. Solar panels in the best U.S. locations hit about 34%, and even the strongest onshore wind sites top out around 47% to 55%. Offshore wind reaches 50% to 58%. Geothermal’s consistency makes it one of the most reliable sources of baseload power available, filling a role that intermittent renewables struggle with on their own.
The Catch: Local Reservoirs Can Run Dry
Calling geothermal “renewable” describes the planet-wide heat supply, not necessarily any single well or reservoir. The Geysers in Northern California is the clearest example. Production there peaked in the late 1980s at about 1,800 megawatts of electricity, then declined roughly 10% per year because of falling reservoir pressure. As steam was extracted faster than the underground system could recharge, pore water converted to vapor, and pressure dropped. A U.S. Geological Survey study on The Geysers went so far as to say the site provided “geophysical observational evidence that geothermal energy is not a renewable energy source” at the local level.
This isn’t a contradiction. It’s the same dynamic you’d see if you pumped water from a well faster than rain could refill the aquifer. The water cycle is renewable; your specific well might not be, depending on how you use it.
How Reinjection Keeps Reservoirs Sustainable
The lesson from The Geysers reshaped how the industry operates. Modern geothermal plants pump cooled water back underground after extracting heat, a process called reinjection. Research on sandstone reservoirs in China found that reinjection is “the dominant factor influencing sustainability.” Without it, maintaining reservoir pressure and hitting long-term production targets is essentially impossible.
Effective reinjection involves more than just pumping water back down a hole. Operators use large-diameter wells, filtration systems to prevent clogging, oxygen-free configurations to avoid corrosion and mineral buildup, and periodic acidification to keep injection pathways open. When these steps are followed, a geothermal reservoir can produce heat for decades or longer without significant decline. When they’re skipped or undersized, you get the pressure drops seen at The Geysers.
A Small Slice of the Energy Mix, for Now
Despite its advantages, geothermal accounts for only about 1% of global electricity demand today. The main barrier has always been geography: conventional geothermal plants need naturally occurring reservoirs of hot water or steam, which limits them to volcanically active regions like Iceland, parts of East Africa, and the western United States.
That geographic limitation is starting to shrink. Enhanced geothermal systems (EGS) borrow horizontal drilling and hydraulic fracturing techniques from the oil and gas industry to create artificial reservoirs where none exist naturally. The first large-scale commercial EGS plant in the United States is under construction and scheduled to come online in June 2026, with a planned capacity of 53 megawatts. Two additional generators of the same size at the same location are expected to begin operating in January 2027, and the developer has signed power purchase agreements totaling 320 megawatts with Southern California Edison for further expansion in 2028.
Other companies are pushing into new territory. Meta signed an agreement with geothermal developer SAGE for up to 150 megawatts of power east of the Rocky Mountains, a region with no existing geothermal generation. A separate company is piloting a closed-loop system designed for hot sedimentary rock common across the western U.S. and Gulf Coast, targeting operation by January 2028. The U.S. Geological Survey estimates that EGS could unlock 135 gigawatts of potential generation in the Great Basin of the Southwest alone. A 2023 estimate from the National Laboratory of the Rockies projected 90 gigawatts of economically viable EGS capacity nationwide by 2050.
The International Energy Agency’s 2024 report on geothermal estimated that next-generation systems could meet up to 15% of global electricity demand growth through 2050, assuming continued cost reductions and technology improvements. That would represent a dramatic shift from the current 1% share.
Renewable With an Asterisk
Geothermal energy is renewable in the same way a forest is renewable: the underlying resource regenerates naturally, but it can be damaged or exhausted locally through careless management. Earth’s heat supply will outlast human civilization by billions of years. Individual wells and reservoirs, however, need proper engineering, particularly water reinjection, to remain productive over decades. The classification as renewable is accurate at the planetary scale, and increasingly accurate at the project level as the industry applies what it learned from early overexploitation. State renewable portfolio standards across the U.S. include geothermal as an eligible source, and federal agencies treat it the same as solar and wind for policy and incentive purposes.