An underground tech surfaces as a serious clean energy contender

A once-overlooked technology that taps into the Earth’s heat to generate electricity could supply up to 20% of the electricity in the United States by 2050, according to a new Princeton analysis.

Published in Joule, the study found that if the costs of deploying enhanced geothermal systems (EGS) fall as more of the technology is implemented—following trends observed in other energy technologies—then it could emerge as the third-most significant clean energy technology behind wind and solar.

The analysis demonstrated that over 250 gigawatts of enhanced geothermal could be deployed by 2050 if the technology can be implemented at baseline or lower-than-expected costs. By comparison, today’s grid has a total capacity of around 1,200 gigawatts.

With more ambitious federal policies, such as a net-zero by 2050 policy, even the most expensive cost estimates for enhanced geothermal led to over 500 gigawatts of deployment by 2050, including in areas east of the Mississippi River historically seen as low-quality geothermal resources.

“Assuming that support for clean firm power from the Inflation Reduction Act remains in place, we found that EGS could very plausibly become a very large percentage of electricity generation across the entire United States,” said first author Wilson Ricks, a postdoctoral researcher at the Andlinger Center for Energy and the Environment. “Planners and policymakers should be taking it seriously as a technology.”

How does enhanced geothermal work?

Enhanced geothermal involves drilling deep underground through hard, hot, and impermeable rocks to form an underground reservoir. Then, cool fluid is pumped into the reservoir at one well and extracted as hot fluid from another. The hot fluid is used to spin a turbine and generate electricity.

Compared to conventional geothermal energy, which is limited to regions with natural superheated reservoirs such as The Geysers in California, enhanced geothermal can be deployed anywhere with hot rocks close enough to the Earth’s surface.

Despite its potential, enhanced geothermal has been overlooked in most energy systems models, partly because the first pilot-scale commercial project in the United States came online only a few years ago. At the same time, cost estimates for the systems depend both on the price of the drilling technology and the rock’s depth and temperature, making it more complex to model than other technologies.

“Unlike with solar, we can’t just look at satellite imagery to determine the best possible sites,” Ricks said. “We need to have people actually dig underground and confirm whether the temperatures and geology are suitable.”

A pathway to commercialization for enhanced geothermal

According to Ricks, enhanced geothermal could have an easier pathway for gaining a foothold in the energy market compared to technologies like advanced nuclear and carbon capture that could similarly provide around-the-clock clean energy. That is because the technology could be able to leverage high-quality geothermal resources to get the first few projects off the ground.

While first-of-a-kind plants for all new technologies are almost always expensive, the price of building more plants typically falls over time as companies gain more skills and experience through a phenomenon known as a learning curve.

At the same time, enhanced geothermal’s reliance on hot rocks yields a kind of resource curve: it is cheaper to deploy where those rocks are close to the surface, such as much of the western United States, and more expensive in areas east of the Mississippi River where hot rocks are farther underground.

Thus, siting first-of-a-kind plants near the best thermal resources could help to offset higher initial building prices, allowing EGS to gain an early footing over similar technologies that would pave the way for commercial liftoff across the country.

Even if today’s policies were repealed, the researchers found that enhanced geothermal might still find a large market in the western U.S. However, they noted that continued federal support is likely critical for allowing the technology to become relevant at a national level.

“The early part of the learning curve, where a technology is at its most expensive and is vying for initial market uptake, is where government support has the greatest impact,” said research leader Jesse Jenkins, an associate professor of mechanical and aerospace engineering and the Andlinger Center for Energy and the Environment. “Continued federal support will be critical for enabling large-scale commercialization of EGS and other emerging technologies.”

While the researchers pointed out that they made assumptions about technology learning rates for EGS that might differ from real-world data, they said their paper is the most empirically grounded and robust cost analysis of EGS to date. They also said their work will be improved as researchers gain a better sense of EGS technology costs and a more precise understanding of subsurface rock temperatures across the country.

“For a long time, it has been models and simulations and theory,” Ricks said. “Now, there’s actual steam coming out of the ground, with pilot scale projects already operating and 100 megawatt projects hopefully coming online soon. We have a lot more information about the technology now than even a few years ago, and we’ve used that information to show that EGS could be a significant player in the future energy system.”