This company wants to use carbon dioxide to store renewable power on the grid

In the quest to find a better way to store power for the grid, an Italian startup is turning to an unlikely source: carbon dioxide. The company, called Energy Dome, has built a test facility to put the greenhouse gas to work in energy storage.

Renewable power has been growing worldwide, but sources like wind and solar aren’t available consistently, creating a need for storage solutions. Today, most large-scale energy storage uses lithium-ion batteries, which are expensive, or pumped hydropower, which is only available in certain places. Cheap energy storage systems that can be deployed anywhere could unlock new potential for renewable power.

Energy Dome thinks carbon dioxide could have a role to play. The company says its demonstration plant, where it has designed and begun trials, will soon be able to safely and cheaply store energy using carbon dioxide sourced from commercial vendors. 

Compressing gases to store energy isn’t new: for decades, a few facilities around the world have been pumping air into huge underground caverns under pressure and then using it to generate electricity in a natural gas power plant. But Energy Dome turned to carbon dioxide because of its physics.

Carbon dioxide, when squeezed to high enough pressures, turns into a liquid, which air doesn’t do unless cooled down to ultra-low temperatures. The liquid carbon dioxide can fit into smaller steel tanks close to where renewable energy is generated and used.

In Energy Dome’s designs, a flexible membrane holds the carbon dioxide in a huge dome at low pressure. When excess electricity is available, the gas goes through a compressor to reach high pressure. This process also generates heat, which is stored too.

Then, when energy is needed, the stored heat is used to warm up the carbon dioxide, which decompresses and turns a turbine, generating electricity.

Energy Dome’s CEO, Claudio Spadacini, says its first full-scale plants should cost just under $200 per kilowatt-hour (kWh), compared with about $300 per kWh for a lithium-ion energy storage system today. Spadacini says that the costs could drop further, to about $100 per kWh, if the company is able to scale up to a few dozen large facilities. 

The concept of compressed carbon dioxide storage is “really promising,” says Edward Barbour, an energy systems researcher at Loughborough University in the UK. However, he expects the company to face some significant engineering challenges, like keeping the heat exchangers working for the decades-long lifetime of the plant. 

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The demonstration facility where Energy Dome recently started trials has a capacity of 4 megawatt-hours, enough to power the average American home for about four and a half months. Spadacini says that after the demonstration facility is running, Energy Dome will move quickly to 200-MWh commercial-scale plants, aiming to begin construction as early as next year at a site in Italy.

The engineering challenges are “not insurmountable, but they’re not insignificant,” Barbour says. That means that the timelines Spadacini has quoted for scale-up might not be feasible, Barbour cautions: “I think there are kinks to be worked out that might take a little bit longer.”