Study suggests geothermal could be an ideal energy storage technology

For parts of the United States, the best place to store a lot of energy for the grid may be right under our feet.

Geothermal energy relies on hot rocks well below the Earth’s surface and has long been used as a source of heating and electricity. But recent advances in drilling technology have opened up new opportunities for widespread deployment of geothermal energy.It prompted researchers at Princeton University to present in an article in the journal Applied Energy Geothermal could also serve as an ideal energy storage technology. What’s more, geothermal can supplement wind and solar energy, providing electricity when the sun is not bright or the wind is calm.

“In the western U.S., which has a lot of geothermal potential, this could be the missing piece of the puzzle to a carbon-free power system with lots of wind and solar power and shorter duration batteries and demand flexibility,” said the project’s principal investigator, Mechanics. said Jesse Jenkins, an assistant professor of aerospace engineering and the Andlinger Center for Energy and the Environment.

Geothermal is an ancient technology that has been used for heating for centuries. Boise, Idaho uses geothermal heat to heat much of the downtown area. In modern times, geothermal has been extended to the power industry, driving heat pumps and supplying electricity to the grid. The advantages of renewable energy technologies include their continuous power generation, relatively low maintenance and zero-carbon production.

But for grid-scale electricity, geothermal remains a niche player. That’s because the technology requires a specific location. Primarily, engineers need hot geological regions very close to the surface, fractured rock formations that act as heat sinks, and fluids to transfer heat to the surface. (Here’s an overview of geothermal power.) That’s changing rapidly as engineers develop new technologies with an eye toward expanding geothermal power firmly.

The key innovation leverages technologies from the oil and gas field, including directional drilling and hydraulic stimulation, to create artificial fracturing systems anywhere hot, impermeable rock can be found. If successful, companies commercializing these new technologies could unlock a clean, renewable resource that could eventually provide hundreds of gigawatts of electricity in the United States alone.

“The ability to move from these very specific locations to the right place with all the right things, to anywhere there is rock that’s hot enough without drilling too deep, means enhanced geothermal could open up a wider range of resources Basics, Jenkins said.

As it turns out, these novel technologies have another hidden advantage that has been overlooked until now. The water circulating through the artificial fracture system is contained in the impermeable rock, which means it cannot leak, making these geothermal reservoirs a great way to store large amounts of energy when demand is low and release it when demand is high. Storing energy and shifting production to when it is most valuable increases geothermal profitability and serves as the perfect complement to weather-dependent variable renewable systems like wind and solar.

“We ran reservoir simulations to evaluate the system we were designing,” said Jack Norbeck, co-founder and chief technology officer of Fervo Energy, a Houston-based developer of these advanced geothermal technologies. Simulations showed that their geothermal system could provide a steady stream of electricity or base load, and also efficiently store and transfer electricity for later use. “We can run them at base load and flexible mode, which is an important step forward for geothermal technology.”

In 2020, Fervo’s engineers are confident that their system will work. But they want to understand the economics of the system and how best to integrate the technology into the grid. To find out, Fervo turned to Jenkins, the head of the Princeton Zero Lab.

“That’s exactly what we like to study,” Jenkins said. “These are practical questions that guide real-world decision-making, investment, and innovation, but have yet to be answered in the academic literature. So this was the perfect project for us — it’s an open question in research, and the answer is today , which is important to the decisions real people are making about how to allocate their time, money and innovation efforts.”

Norbeck, CTO of Fervo, provided technical support for the research. At the heart of the idea, he says, is combining the thermal energy of the subterranean rock with the mechanical energy of the overlying rock formation. Fervo’s engineers use horizontal drilling techniques to create a series of injection and production boreholes that are interconnected by many small channels in the rock, creating an underground reservoir about 10,000 feet below the surface that can heat water. Instead of using the hot water immediately to drive turbines to generate electricity, technicians channel the pressurized hot water into the reservoir’s network of channels. Fluid builds up in the reservoir and bends the rock, then releases the pressure, driving the hot fluid to the surface to power turbines.

The researchers showed that the system can be used to store and dispatch electricity over long periods of time, ranging from hours to days, making it different from most other storage technologies. “Efficiency depends on the geology and other characteristics of the rock,” Nobeck said. But, overall, “this form of energy storage has proven to be one of the cheapest forms of long-term energy storage.”

Wilson Ricks, Ph.D. candidate in mechanical and aerospace engineering and fellow in Zero’s lab, led the study and said the study’s results exceeded his original expectations.

“The idea seemed a bit simple and elegant to me: you have this system, it has these inherent properties, and maybe we can use them for energy storage…like icing on the cake,” said Ricks, the paper’s lead author. “It turns out to be undeniably more valuable in almost all cases, and it’s actually a very large potential advantage.”

The paper “The Value of In-Storage Storage for Flexible Scheduling of Geothermal Power Generation” was published in Applied Energy.

The original paper looked at the impact of a first-of-its-kind plant. But if the technology is deployed at scale, it can change electricity prices or market dynamics, so now the team is using a long-term power capacity planning model to examine long-term equilibrium outcomes and impact on markets. The results of the first study helped Fervo demonstrate the added value of this novel method of storage and was awarded a highly competitive grant from the Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E). The latest project, a joint effort between Fervo, Princeton Zero Lab, Lawrence Berkeley National Laboratory and Rice University, will involve live demonstrations and real-world data collection of artificial fracture networks and in-reservoir performance of energy storage.

“This is what we found really exciting, that you can answer these kinds of open-ended questions with our energy system modeling tools, which then lead directly to further investment and innovation, and hopefully accelerate the adoption of impactful technologies that can help We’re dealing with climate change,” Jenkins said.