Geothermal power heats up
Glistening in the dry expanses of the Nevada desert is an unusual kind of power plant that harnesses energy not from the sun or wind, but from the Earth itself.
The site, known as Project Red, pumps water thousands of feet into the ground, down where rocks are hot enough to roast a turkey. Around the clock, the structure sucks the heated water back up; it is then used to power generators. Since last November, this carbon-free, Earth-borne power has been flowing onto a local grid in Nevada.
Geothermal energy, though it’s continuously radiating from Earth’s super-hot core, has long been a relatively niche source of electricity, largely limited to volcanic regions like Iceland where hot springs bubble from the ground. But geothermal enthusiasts have dreamed of sourcing Earth power in places without such specific geological conditions — like Project Red’s Nevada site, developed by energy startup Fervo Energy.
Such next-generation geothermal systems have been in the works for decades, but they’ve proved expensive and technologically difficult, and have sometimes even triggered earthquakes. Some experts hope that newer efforts like Project Red may now, finally, signal a turning point, by leveraging techniques that were honed in oil and gas extraction to improve reliability and cost-efficiency.
The advances have garnered hopes that with enough time and money, geothermal power — which currently generates less than 1 percent of the world’s electricity, and 0.4 percent of electricity in the United States — could become a mainstream energy source. Some posit that geothermal could be a valuable tool in transitioning the energy system off of fossil fuels, because it can provide a continuous backup to intermittent energy sources like solar and wind. “It’s been, to me, the most promising energy source for a long time,” says energy engineer Roland Horne of Stanford University. “But now that we’re moving towards a carbon-free grid, geothermal is very important.”
A rocky start
Geothermal energy works best with two things: heat, plus rock that is permeable enough to carry water. In places where molten rock sizzles close to the surface, water will seep through porous volcanic rock, warm up and bubble upward as hot water, steam or both.
If the water or steam is hot enough — ideally at least around 300 degrees Fahrenheit — it can be extracted from the ground and used to power generators for electricity. In Kenya, nearly 50 percent of electricity generated comes from geothermal. Iceland gets 25 percent of its electricity from this source, while New Zealand gets about 18 percent and the state of California, 6 percent.
Some natural geothermal resources are still untapped, such as in the western United States, says geologist Ann Robertson-Tait, president of GeothermEx, a geothermal energy consulting division at the oilfield services company SLB. But by and large, we’re running out of natural, high-quality geothermal resources, pushing experts to consider ways of extracting geothermal energy from areas where the energy is much harder to access. “There’s so much heat in the Earth,” Robertson-Tait says. But, she adds, “much of it is locked inside rock that isn’t permeable.”
Tapping that heat requires deep drilling and creating cracks in these non-volcanic, dense rocks to allow water to flow through them. Since 1970, engineers have been developing “enhanced geothermal systems” (EGS) that do just that, applying methods similar to the hydraulic fracturing — or fracking — used to suck oil and gas out of deep rocks. Water is pumped at high pressure into wells, up to several miles deep, to blast cracks into the rocks. The cracked rock and water create an underground radiator where water heats before rising to the surface through a second well. Dozens of such EGS installations have been built in the United States, Europe, Australia and Japan — most of them experimental and government-funded — with mixed success.
Famously, one EGS plant in South Korea was abruptly shuttered in 2017 after having probably caused a 5.5 magnitude earthquake; fracking of any kind can add pressure to nearby tectonic faults. Other issues were technological — some plants didn’t create enough fractures for good heat exchange, or fractures traveled in the wrong direction and failed to connect the two wells.
Some efforts, however, turned into viable power plants, including several German and French systems built between 1987 and 2012 in the Rhine Valley. There, engineers made use of existing fractures in the rock.
But overall, there just hasn’t been enough interest to develop EGS into a more reliable and lucrative technology, says geophysicist Dimitra Teza of the energy research institute Fraunhofer IEG in Karlsruhe, Germany, who helped develop some of the Rhine Valley EGS systems. “It has been quite tough for the industry.”
New momentum
Solutions exist for both safety and technological problems. There are, in fact, robust protocols for avoiding earthquakes, such as by not drilling near active faults. Long-term monitoring of the operating EGS plants in France and Germany has documented only minor tremors, building confidence in the safety of the technology. Importantly, drilling and fracking methodology has improved by leaps and bounds, thanks to the boom in oil and gas extraction from shale rocks that began in the 2010s. “Since then, we’ve seen a renewed interest in EGS as a concept, because the techniques that are central to EGS were perfected and brought down significantly in cost during that time,” says Wilson Ricks, an energy systems researcher at Princeton University.
In 2015, for instance, the US Department of Energy launched a research site in Utah dedicated to advancing EGS technologies. Several new North American startups, including Sage Geosystems and E2E Energy Solutions, are developing new EGS systems in Texas and Canada, respectively. The most advanced is Fervo Energy, which has applied several techniques from the shale industry at its Nevada site; the electricity now supplies a local grid that includes energy-sucking data storage centers owned by Google. (Google partnered with Fervo to develop the plant.)
Engineers drilled almost 8,000 feet downward into the Nevada rock, reaching temperatures of nearly 380 degrees Fahrenheit, and then, at the bottom, drilled another 3,250-foot horizontal well to expand the area of hot rock that the system touches — a technique used in oil and gas extraction in order to maximize yield. The company also fractured the surrounding rock at several sites along the horizontal well to create a more extensive web of cracks for water to trickle through. Technologically speaking, compared to earlier EGS efforts, “they are, in fact, a big step forward,” says Horne, who is on Fervo’s scientific advisory board.
It remains to be seen how these new EGS systems perform in the long term. One advantage of systems like Fervo’s is that they can be made more profitable by taking advantage of energy price fluctuations, according to recent research by Ricks, a Princeton colleague and several experts at Fervo Energy. Operators could plug the exit wells, causing water to accumulate inside the system, building up pressure and heat. Then the energy could be extracted during times when it is most valuable — such as during cloudy or windless periods when solar or wind aren’t working.
Still, such systems would have to be significantly scaled up to be commercially viable, Ricks says. Although Project Red provided enough steam to generate 3.5 megawatts, enough to power more than 2,500 homes and more than any other EGS plant, it’s still relatively small; a nuclear or coal plant can easily have an output of 1,000 megawatts, while large solar or traditional geothermal plants often produce several hundred megawatts.
What the EGS field needs right now, Ricks says, is the funding to build and test more such systems to inspire investor confidence. “This all needs to be very well proven, out to the point where the perceived risk is low,” he says.
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A turning point for geothermal?
To that end, the US Department of Energy recently awarded $60 million in funding to three demonstration projects for EGS and related technologies as part of a broader initiative to speed up EGS development. One 2019 report from the agency estimated that, with advances in EGS, geothermal power could represent around 60 gigawatts (60,000 megawatts) of installed capacity in the United States by 2050, generating 8.5 percent of the country’s electricity — a more-than-20-fold increase from today.
Even an increase of a few percent could aid in a global energy transition that’s aiming to get to net zero carbon emissions by 2050. “If in fifteen, twenty years, EGS is viable, I think it could play a huge part,” says Nils Angliviel de La Beaumelle, who recently coauthored an article on the global outlook for renewable energy in the Annual Review of Environment and Resources.
Other geothermal technologies may also help. Some companies are exploring the feasibility of “super hot rock” geothermal — essentially, a young, extreme variant of EGS that involves drilling down even deeper into Earth’s crust, to a depth where water reaches a “supercritical” vapor-like state that allows it to carry much more energy than either steam or liquid. In southern Germany, the energy company Eavor is building the world’s first “closed-loop” geothermal system: Once pipes funnel water into the deep rock, the system fans out into a network of parallel boreholes, without water ever penetrating the rock. That’s a more predictable — albeit less efficient — way of warming water, as it doesn’t involve uncertainties around fracturing the rock in the right way, Teza says. “I’m really excited to see that there’s investment into these technologies,” she says. “I think it can only help.”
On the whole, it’s an important moment for geothermal energy — and not just for providing carbon-free electricity, Robertson-Tait says. Geothermal brines hauled out of the Earth are rich in lithium and other critical minerals that can be used to build green technologies like solar panels and EV batteries. There’s a growing push to use direct geothermal heat to warm buildings, either through shallow heat pumps for residential buildings or larger systems designed for entire districts — like Paris and Munich already have.
Some oil and gas companies, recognizing that a change is coming, are increasingly interested in building geothermal systems of various kinds, says Robertson-Tait. “Our Earth is geothermal,” she says, “and so I think we owe it to ourselves to do everything we can to use it.”
Editor’s note: This story was updated on April 22, 2024, to correct a mischaracterization of Project Red as a power plant. In fact, Project Red includes only the EGS infrastructure. The electricity itself is generated by a power plant under ownership of another company. A caption was also updated to correct the spelling of Larderello in Italy.
This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews. Sign up for the newsletter.
