Storing Renewable Energy, One Balloon at a Time

To decarbonize the electrical grid, companies are finding creative ways to store energy during periods of low demand.

Central Sardinia is not generally considered a hotbed of innovation: Arid and rural, some of its road signs riddled with bullet holes made by target-practicing locals, the setting recalls a Clint Eastwood western. Yet in Ottana, on the brownfield site of a former petrochemical plant, a new technology is taking shape that might help the world slow climate change. The key component of this technology is as unlikely as the remote location: carbon dioxide, the chief cause of global warming.

Energy Dome, a start-up based in Milan, runs an energy-storage demonstration plant that helps to address a mismatch in the local electricity market. “In Sardinia during the day, everyone goes to the sea,” Claudio Spadacini, chief executive of Energy Dome, said. “They don’t use electricity, but there’s a lot of supply,” he added, referring to the Italian island’s abundant sunlight.

Energy Dome uses carbon dioxide held in a huge balloon, the “dome” in the company’s name, as a kind of battery. During the day, electricity from the local grid, some produced by nearby fields of solar cells, is used to compress the carbon dioxide into liquid. At night, the liquid carbon dioxide is expanded back into gas, which drives a turbine and produces electricity that is sent back to the grid.

Solar and wind power are fast-growing renewable sources, but they rely on nature’s intermittent schedule to produce electricity. Many researchers and policymakers say that storing such energy until needed, for hours or even days, is key to transitioning economies away from fossil fuels. “Advancing energy-storage technologies is critical to achieving a decarbonized power grid,” Jennifer M. Granholm, the U.S. energy secretary, said in a 2022 statement, when her department announced that it would commit more than $300 million for long-duration energy storage.

Companies are developing and marketing varied and creative ways to store renewable energy: liquefying carbon dioxide, de-rusting iron, heating towers filled with sand to temperatures almost hot enough to melt aluminum. But predicting our energy-storage needs in the future, after a huge energy transformation, is a daunting prospect, and which of these approaches, if any, will prove effective and profitable is unclear.

“There is a real urgency around decarbonizing electricity on a timeline that is much faster than we’ve contemplated in the past,” said Elaine Hart, founding principal with Moment Energy Insights LLC, a clean-energy consultancy. “We don’t need technologies like long-duration energy storage or hydrogen today, but we might need them on a large scale in the next 15 to 20 years, so we’re in a critical time for their development.”