Giant Underground ‘Batteries’ Are Shaping the Future of Renewable Energy Storage

Solar panels and wind turbines give the world bountiful energy—but come with a conundrum. When it’s sunny and windy out, in many places these renewables produce more electricity than is actually needed at the time. Then when the Sun isn’t shining and wind isn’t blowing, those renewables provide little to no electricity when it’s sorely needed.

So for the grid of tomorrow to go 100% renewable, it needs to store a lot more energy. You’ve probably heard about giant lithium-ion batteries stockpiling that energy for later use. But when providing backup power, even a big battery bank will usually drain in four hours. The need for an alternative has the United States government, researchers, and startups scrambling to develop more “long-duration energy storage” that can provide a minimum of 10 hours of backup power—often by using reservoirs, caverns, and other parts of the landscape as batteries.

A new study from several universities and national labs in the United States and Canada shows that large-scale deployment of long-duration energy storage isn’t just feasible but essential for renewables to reach their full potential, and would even cut utility bills. It looked specifically at the Western Interconnection, a chunk of the grid that includes the western U.S. and Canada, plus a bit of northern Mexico. The study found that building more long-duration energy storage there would reduce electricity prices by more than 70% in times of high demand.

“It’s like an orchestra,” said Patricia Hidalgo-Gonzalez, director of the Renewable Energy and Advanced Mathematics Laboratory at the University of California, San Diego and coauthor of the paper published last month in the journal Nature Communications. “We need to think about all these factors, how they work. But bringing in more storage can only help in making this more cost-effective.”

The technologies already exist to hold renewable energy for at least half a day, with more on the way. One technique is known as pumped storage hydropower: When the grid is humming with renewable power, a facility pumps water uphill into a reservoir. Then, when solar or wind power drops off, the facility lets the water loose to flow back down into another reservoir, turning turbines that produce electricity. It’s exploiting energy from the wind and the sun, along with the power of gravity.

“Battery storage on its own—or what people call short-duration energy storage—is very important,” said Martin Staadecker, an energy systems researcher at the Massachusetts Institute of Technology and lead author of the new study. “But you can’t just rely on lithium-ion batteries, because it would be very expensive to have enough to actually provide power for an entire week.”

As of 2022, the U.S. had 43 pumped storage hydropower facilities with a combined generation capacity of 22 gigawatts. (For perspective, the U.S. has around 150 gigawatts of wind power and 140 gigawatts of solar.) According to the Department of Energy, the U.S. has the potential to double its capacity for that kind of energy storage. In 2021, the Biden administration launched its Long Duration Storage Shot, part of the Energy Earthshots initiative, aiming to reduce the costs of the technology by 90% in a decade. And last year, it announced $325 million for 15 long-duration energy storage projects, including one that stores heat energy in concrete and others to make newfangled batteries made of iron, water, and air.

The researchers looked at long-duration energy storage without considering the particular technique involved, asking what would be the cheapest way to get the Western Interconnection to be 100% emissions-free. Their study found that long-duration energy storage would be particularly beneficial to a utility’s customers, reducing electricity costs in times of high demand on the grid, like in the late afternoon as people return home and switch on appliances at the same time that solar power on the grid is waning. More storage also means more backup power for ever-hotter heat waves, when whole regions flick on their AC units.

Companies are figuring out how to store energy underground, too. A company called Hydrostor, based in Toronto, Canada, uses excess renewable energy on the grid to pump compressed air into subterranean caverns filled with water. That forces the water aboveground into a reservoir. When the grid needs electricity, Hydrostor lets that water flow back into the chamber, pushing the air back to the surface to drive turbines. “We’re kind of creating a piston underground of water,” said Jon Norman, president of Hydrostor. “We’re actually building a cavity out using techniques that they use in the hydrocarbon storage industry to store propane and butane.”

If a region runs low on renewable power, like when the Sun sets, it would have to import carbon-free electricity from elsewhere. But that requires transmission lines that cut through hundreds or thousands of miles of land, which are difficult to get approved and expensive to build. The new study found that it would cost between $83 billion and $130 billion to deploy the amount of long-duration energy storage in the modeling—depending on how the price of the technology declines as it matures.

With long-duration energy storage, utilities can deploy more solar panels and wind turbines locally and store up their energy, rather than having to ship it from somewhere else. Kevin Schneider, an electrical engineer who studies the grid at the Pacific Northwest National Laboratory but wasn’t involved in the new research, said that could reduce the significant costs of building long-distance transmission lines. “Getting that flexibility in the system, where you can have a reservoir of electricity that you can store up and then release, that’s what allows us to not have to build as much infrastructure, and also be a little bit more resilient.”

The grid of tomorrow, then, may hum with renewable energy stored both in giant battery banks, but also stored in the landscape itself. Solar and wind power would be wasted no more.

This article originally appeared in Grist at https://grist.org/climate/long-duration-energy-storage-batteries-store-solar-wind-power/. Grist is a nonprofit, independent media organization dedicated to telling stories of climate solutions and a just future. Learn more at Grist.org.