Geothermal energy is one of the cleanest power sources available, but it comes with real drawbacks: high upfront costs, earthquake risk from drilling, toxic fluids pulled up from underground, and strict geographic limitations that keep it from scaling the way solar and wind have. None of these problems make geothermal a bad choice everywhere, but they explain why it supplies less than 1% of global electricity despite decades of development.
Earthquake Risk From Drilling
The most headline-grabbing problem with geothermal energy is that it can trigger earthquakes. Conventional geothermal plants tap into naturally hot, permeable rock, which carries a relatively low seismic risk. Enhanced geothermal systems (EGS), however, work by injecting fluid at high pressure into deep, impermeable rock to fracture it and create pathways for heat extraction. That pressurized fluid can reactivate faults that were previously stable, producing earthquakes large enough for people to feel at the surface.
A notable example occurred in Basel, Switzerland, in 2006, when an EGS project triggered a magnitude 3.4 earthquake that damaged buildings and led to the project’s cancellation. The risk doesn’t disappear once drilling stops, either. During the circulation phase, when a plant is actively producing energy, seismic risks persist, just driven by different mechanisms than during the initial fracturing. Operators now use traffic-light protocols that pause injection when seismic activity crosses certain thresholds, but the technology is still evolving, and no system can guarantee zero risk.
Toxic Fluids and Air Emissions
Geothermal wells pull up more than just heat. The hot brine circulating deep underground dissolves heavy metals and other harmful elements on its way to the surface. Chemical analyses of geothermal brines have found elevated concentrations of arsenic, lead, zinc, cadmium, antimony, copper, and uranium. If these fluids leak into local waterways or soil, they pose a serious contamination risk. Modern closed-loop systems reinject the brine back underground, which greatly reduces the danger, but leaks and equipment failures remain possible.
Geothermal plants also release gases. The average plant emits about 0.18 pounds of carbon dioxide per kilowatt-hour, roughly one-twelfth the emissions of a coal plant (2.13 lbs/kWh) and about one-sixth of natural gas (1.03 lbs/kWh). That’s a massive improvement over fossil fuels, but it’s not zero. Plants also release small amounts of hydrogen sulfide, the gas responsible for a rotten-egg smell. While the quantities are tiny (about 0.000187 lbs/kWh), communities near geothermal fields can experience chronic low-level exposure.
Health Effects of Hydrogen Sulfide
Research on communities living near geothermal areas paints a mixed picture. In Rotorua, New Zealand, a city of about 60,000 people sitting directly on a geothermal field, long-term studies of over 1,200 residents found no evidence of reduced lung function or increased risk of COPD or asthma from hydrogen sulfide exposure, even at the highest measured levels. In Reykjavik, Iceland, however, researchers found that when ambient hydrogen sulfide levels exceeded 7.0 micrograms per cubic meter, emergency hospital visits for heart disease increased, particularly among men and people over 73. A separate study in Tuscany, Italy, tracked over 33,000 residents near geothermal areas from 1980 to 2016 and found a small but statistically significant 12% increase in deaths from respiratory diseases for each 7 microgram-per-cubic-meter rise in exposure. The overall risk appears low, but it’s not negligible for people living closest to plants over many years.
High Costs and Financial Risk
Geothermal energy is expensive to get started. Before a single watt of electricity is generated, developers must drill exploratory wells thousands of feet deep, with no guarantee of finding a viable resource. For near-field enhanced geothermal systems, exploration drilling succeeds about 76% of the time under conservative estimates. For deep EGS projects, the success rate drops to roughly 52%, meaning nearly half of exploratory wells come up empty. Each failed well can cost millions of dollars.
Once a viable site is confirmed, building the plant itself is capital-intensive. Overnight construction costs for hydrothermal plants tapping the hottest resources (200°C and above) average around $4,350 per kilowatt of capacity. For lower-temperature resources below 135°C, that figure balloons to nearly $19,000 per kilowatt. By comparison, utility-scale solar and onshore wind projects typically cost $1,000 to $1,500 per kilowatt.
These upfront costs ripple into the final price of electricity. The U.S. Energy Information Administration projects that geothermal plants entering service in 2030 will produce electricity at a levelized cost of about $53 to $59 per megawatt-hour. That’s competitive with some fossil fuels, but it’s roughly double the cost of onshore wind ($26 to $30/MWh) and noticeably more expensive than solar ($32 to $38/MWh). Geothermal’s advantage is that it runs 24 hours a day regardless of weather, which is genuinely valuable. But the price gap discourages investment when cheaper renewables are available.
Geographic Limitations
You can install solar panels almost anywhere the sun shines. Geothermal plants need a very specific geology: permeable rock with high heat close to the Earth’s surface. In practice, this has limited geothermal power to regions with significant tectonic activity, including California, Iceland, Indonesia, the Philippines, and parts of Central America. Most of the world simply doesn’t have the right underground conditions for conventional geothermal development.
Enhanced geothermal systems aim to change this by engineering the underground conditions rather than relying on natural ones. The concept works in theory, and pilot projects are underway. But as noted above, EGS carries higher seismic risk, higher drilling failure rates, and higher costs. Until those problems are solved at scale, geothermal energy will remain a niche contributor to the global energy mix rather than a universal solution.
Water Use
Geothermal plants consume water, though significantly less than fossil fuel power plants. Binary cycle plants, the most common modern design, use between 0.24 and 4.21 gallons per kilowatt-hour. Flash plants, which release hot brine into a low-pressure tank to create steam, consume 1.59 to 2.84 gallons per kilowatt-hour. For context, conventional coal and gas plants used an average of about 15 gallons per kilowatt-hour as recently as 2015. Geothermal’s water footprint is modest by power-generation standards, but it can still strain local supplies in arid regions where geothermal resources often happen to be located.
Land Subsidence
Extracting large volumes of hot fluid from underground reservoirs can cause the ground above to sink. The most dramatic example is Wairakei in New Zealand, where decades of geothermal production have caused up to 15 meters (about 49 feet) of total subsidence, with peak rates exceeding 450 millimeters per year. A nearby highway sank roughly 8 meters over the life of the field. A resort hotel on the property subsided by 4 meters. Horizontal ground movement at the site reached 4.3 meters between 1967 and 2000.
Wairakei is an extreme case, partly because early operations did not reinject spent fluids. Neighboring fields like Tauhara and Ohaaki, which experienced pressure drawdown from Wairakei’s production, saw lower but still meaningful subsidence of 2 to 3 meters total. Modern plants mitigate this by reinjecting fluids to maintain underground pressure, but subsidence remains a monitoring concern at any large-scale geothermal operation, especially near infrastructure or populated areas.