Storing renewable energy, one balloon at a time

Central Sardinia is generally not considered a hotbed of innovation: arid and rural, and some road signs are riddled with bullet holes made by local shooting sportsmen. The setting is reminiscent of a Clint Eastwood western. But in Ottana, on the brownfield site of a former petrochemical plant, a new technology is taking shape that could help the world slow climate change. The most important part of this technology is as unlikely as its remote location: carbon dioxide, the main cause of global warming.

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

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

Solar and wind energy are fast-growing renewable sources, but they depend on nature’s irregular schedule to produce electricity. Many researchers and policymakers say that storing such energy until it is needed, for hours or even days, is critical to weaning economies away from fossil fuels. “Advancing energy storage technologies is critical to achieving a carbon-free electric grid,” said Jennifer M. Granholm, U.S. Secretary of Energy. in a 2022 statementwhen her department announced it would commit more than $300 million to long-term energy storage.

Companies are developing and selling varied and creative ways to store renewable energy: liquefying carbon dioxide, derusting iron, filling heating towers with sand to temperatures almost high enough to melt aluminum. But predicting our energy storage needs in the future, following a massive 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 have considered in the past,” said Elaine Hart, founder and principal of Moment Energy Insights LLC, a clean energy consultancy . “We don’t need technologies like long-term energy storage or hydrogen today, but we may need them at scale in the next 15 to 20 years, so we are at a critical time for their development.”