Giant Underground Pools of Water Are Batteries of the Future

In an energy-efficient future, homes may be heated and cooled by pumping from giant pools of water stored underground. A study published this month in Applied Energy looks at how underground aquifers could help significantly reduce reliance on fossil fuels and help store energy produced by renewables.

The research deals with a technology known as aquifer thermal energy storage, or ATES. Water is a great way to store thermal energy, and the Earth is an efficient insulator. ATES is simply the process of using water stored naturally underground in aquifers to heat and cool homes: pumping warm water through one well in the winter to heat homes and using a separate pump to extract that same water in the summer for cooling purposes.

This new study, conducted by a group of researchers at Lawrence Berkeley National Laboratory, looks at how ATES technology could interact with other forms of energy on the grid—namely, by storing excess energy produced by renewables by using that energy to heat the water before it’s pumped underground.

“When we think of energy storage and intermittency of renewables, we almost always talk about batteries right away,” Peter Nico, a biogeochemist at the Berkeley Lab and coauthor of the paper, told Earther in an email. “Batteries are great, but there are lots of other creative ways to store energy, and the ground beneath our feet can help with that.”

For the study, the team modeled a scenario around the use of ATES in a neighborhood in Chicago, creating a hypothetical neighborhood of around 60 homes that were hooked up to a grid that could provide different forms of energy and storage. They then ran that model through various climate scenarios to get a sense of how much heating and cooling these homes will need in the future, as well as testing out the grid’s resiliency during disasters.

The model showed some pretty huge benefits. The use of ATES drove down the grid’s use of fossil fuels for energy by up to 40% in some cases. What’s more, ATES also made the grid more resilient during hypothetical future heat waves: Unlike air conditioners that stress the grid during super-hot days, ATES cooling needs just enough energy to pump water around.

Like heat pumps, this technique seems so simple that it sounds too good to be true—but ATES isn’t a perfect technology. The location where ATES is set up must have access to natural aquifers with specific attributes to help the water flow more efficiently. And there are cost restrictions. The study found that ATES could be up to 20% more expensive than other energy storage options on the market.

Despite these concerns, the study authors say that continuing to develop the technology could help bring down costs. Many of the world’s ATES projects are in the Netherlands; studies have shown that both Germany and Spain have great potential for the technology, and the researchers say there are large portions of the U.S. that would also benefit from ATES.

“I don’t know why [ATES] hasn’t taken off more in the U.S.,” Nico said. “Very roughly, I would guess something about cost and about familiarity. It is hard to be an early adopter. Overall, getting the initial capital costs of installation down would help a lot with the overall cost effectiveness.”

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