Geothermal energy is renewable. The heat flowing from Earth’s interior is continuously replenished by the decay of naturally occurring radioactive elements and will remain available for billions of years. That puts it in a different category from fossil fuels, which exist in fixed quantities, but also in a different category from solar and wind, because geothermal can produce power around the clock regardless of weather.
Why Earth’s Heat Won’t Run Out
The planet’s core sits at roughly 5,000°C, and that heat migrates slowly outward through the mantle and crust. Two processes keep it going: leftover thermal energy from Earth’s formation about 4.5 billion years ago, and the ongoing breakdown of radioactive isotopes in the mantle and crust. Together, these sources produce heat at a rate that far exceeds what any geothermal operation could extract. On any timescale relevant to human civilization, the supply is essentially limitless.
That said, individual geothermal reservoirs can be depleted if heat or fluid is drawn out faster than it’s replaced. This is an important distinction. The energy source itself is renewable, but a specific well or field needs careful management to stay productive. The Larderello geothermal field in Italy, where wells have been producing power for over 100 years, demonstrates that with proper stewardship, a single site can operate for generations.
How Geothermal Plants Capture That Heat
Three main power plant designs convert underground heat into electricity, each suited to different reservoir conditions.
Dry steam plants tap reservoirs that produce steam directly. That steam spins a turbine to generate electricity. These are the simplest systems but require a rare type of reservoir.
Flash steam plants are the most common type worldwide. They pump high-pressure hot water from deep underground to the surface, where the sudden pressure drop causes some of it to “flash” into steam. That steam drives a turbine. Once it cools and condenses back into water, it gets injected back into the reservoir.
Binary cycle plants work with lower-temperature water that isn’t hot enough to flash into steam on its own. Instead, the hot water passes its heat to a second liquid with a much lower boiling point. That second liquid vaporizes and spins the turbine. The geothermal water never contacts the turbine and goes straight back underground. Because it’s a closed loop, this design produces no air emissions.
The Baseload Advantage Over Solar and Wind
What makes geothermal unusual among renewables is reliability. A geothermal plant runs whether the sun is shining or not, whether the wind is blowing or not. Globally, geothermal plants operate at about 75% of their maximum capacity on average. Solar panels, by comparison, average around 11 to 12%, and wind turbines around 22 to 23%. That means a 100-megawatt geothermal plant produces roughly three to four times more actual electricity per year than a 100-megawatt wind farm and six to seven times more than a 100-megawatt solar installation.
This makes geothermal well suited for baseload power, the steady, always-on electricity supply that a grid needs to function. Solar and wind are excellent at adding clean capacity, but they need storage or backup for nighttime and calm days. Geothermal doesn’t have that problem.
Emissions Are Low but Not Zero
Geothermal power produces far less CO₂ than fossil fuels, but it isn’t emission-free in every case. The global average sits around 122 grams of CO₂ per kilowatt-hour. For context, natural gas plants emit roughly 450 g/kWh, and coal is higher still. Some geothermal fields perform dramatically better: Iceland’s plants average just 34 g/kWh, while California comes in around 107 g/kWh.
However, certain geologic settings can push emissions much higher. Some sites in Italy and Turkey release over 500 g/kWh, with a few exceeding 1,000 g/kWh, putting them on par with coal. These are outliers driven by unusual underground chemistry, but they show that not every geothermal project has an equally clean profile. Binary cycle plants, which keep geothermal fluids in a sealed loop, avoid this issue almost entirely.
Water Use and Reservoir Management
Geothermal plants need water, primarily for cooling. How much depends on the cooling system. Dry-cooled plants use almost nothing, averaging 0.04 gallons per kilowatt-hour. Wet-cooled flash plants average about 2.4 gallons per kWh, and wet-cooled binary plants average 3.4 gallons per kWh. Hybrid systems split the difference at around 1.0 gallon per kWh.
Reinjection is the other major water consideration. Binary plants almost always operate as closed loops, returning all produced fluid to the reservoir. Flash plants don’t always reinject, and skipping that step shortens the reservoir’s productive life. At least three major U.S. geothermal operations, including The Geysers in California, have run supplemental injection programs to sustain declining reservoirs. Finding compatible low-quality water sources for reinjection is one of the bigger practical challenges for long-term geothermal sustainability.
Cost Compared to Other Renewables
Geothermal electricity costs more upfront than solar or wind. For new plants expected to come online around 2030, the U.S. Energy Information Administration estimates a levelized cost of about $53 to $59 per megawatt-hour for geothermal. Onshore wind comes in at roughly $19 to $26 per MWh, and solar at $30 to $32 per MWh.
Those numbers don’t tell the whole story, though. Geothermal’s high capacity factor means you need far less installed capacity to produce the same amount of electricity. And because geothermal delivers power around the clock, it doesn’t require the battery storage costs that solar and wind eventually face at grid scale. The upfront drilling and exploration costs are the main barrier, since you’re essentially prospecting underground before you know exactly what you’ll find.
Enhanced Systems Could Unlock Geothermal Everywhere
Traditional geothermal requires three things to exist naturally in the same place: heat, underground fluid, and permeable rock that lets that fluid circulate. That combination is common near tectonic plate boundaries but rare elsewhere, which is why global geothermal capacity was only about 15 gigawatts at the end of 2024, a tiny fraction of total renewable capacity.
Enhanced geothermal systems (EGS) aim to change that. In locations where hot rock exists but lacks natural fluid or permeability, EGS creates an artificial reservoir. Fluid is injected deep underground under controlled conditions to open new fractures and reopen existing ones in the rock. That fractured rock then allows fluid to circulate, heat up, and return to the surface for power generation. The principle is the same as conventional geothermal, but the reservoir is engineered rather than found.
If EGS technology matures at scale, geothermal energy could expand well beyond volcanic regions and tectonic boundaries. Hot rock exists at reachable depths almost everywhere on Earth. The limiting factor has always been accessing it economically. New Zealand, Indonesia, Turkey, and the United States led geothermal expansion in 2024, but EGS could eventually make geothermal viable in regions that have never had access to it.