The Massive ‘Batteries’ Hidden Beneath Your Feet

“These systems are quite ideal when integrating renewables,” says energy systems researcher A.T.D. Perera, lead author of the new paper. (Perera is now at Princeton University but did the research while at Lawrence Berkeley National Laboratory.)

This technology is not yet widely deployed globally. Some 85 percent of the ATES systems are in the Netherlands, which has both the right geology and stringent national standards for energy efficiency. But one study found that swathes of Germany are suited for it; another found that almost a third of Spain’s population lives in areas suitable for ATES. 

Not every area is a good fit, though. Unlike, say, a natural-gas power plant, a geothermal energy system depends on a host of complex geological factors. “It would be really, really difficult to say ‘OK, this system works well where I live in Illinois’ and then try to translate it to your home in California,” says Yu-Feng Lin, a geoscientist at the University of Illinois at Urbana-Champaign. (Lin is part of the international consortium with Burns but wasn’t involved in the new paper.) “It’s not as simple as copy-paste.”

For example, a city built on solid rock has no easy access to an aquifer. And even one that does have access needs sufficient “hydraulic conductivity,” meaning that water easily flows through underground materials like sand and gravel. The better the water flows, the easier and less energy-intensive it’ll be to pump it out. 

That said, it can’t flow too much, because when you pump water down it may migrate elsewhere across the landscape. “You want it to flow when you want it to flow,” says Peter Nico, a geoscientist at Lawrence Berkeley National Laboratory who coauthored the paper with Perera. Luckily for the United States, Nico adds, “there are large swaths of the country that are in good shape for it.”

But there is another challenger: ATES is expensive. It requires thoroughly studying a given city’s geology, then paying to drill and set up the pumping equipment. But at least that cost is up front: Once you’ve got wells and pumps, it all runs on abundant, free solar or wind power. Plus, it’s not taking up much space at the surface, leaving room for urban gardens and other open green areas that cities need more than ever. “If you’re willing to pay a little bit more in order to improve climate resilience or become more sustainable,” says Perera, “this would be an ideal way to go.”