This giant bubble on the island of Sardinia holds 2,000 tonnes of carbon dioxide. But the gas wasn’t captured from factory emissions, nor was it pulled from the air. It came from a gas supplier, and it lives permanently inside the dome’s system to serve an eco-friendly purpose: to store large amounts of excess renewable energy until it’s needed.
Developed by the Milan-based company Energy Dome, the bubble and its surrounding machinery demonstrate a first-of-its-kind “CO2 Battery,” as the company calls it. The facility compresses and expands CO 2 daily in its closed system, turning a turbine that generates 200 megawatt-hours of electricity, or 20 MW over 10 hours. And in 2026, replicas of this plant will start popping up across the globe.
We mean that literally. It takes just half a day to inflate the bubble. The rest of the facility takes less than two years to build and can be done just about anywhere there’s 5 hectares of flat land.
The first to build one outside of Sardinia will be one of India’s largest power companies, NTPC Limited. The company expects to complete its CO2 Battery sometime in 2026 at the Kudgi power plant in Karnataka, in India. In Wisconsin, meanwhile, the public utility Alliant Energy received the all clear from authorities to begin construction of one in 2026 to supply power to 18,000 homes.
And Google likes the concept so much that it plans to rapidly deploy the facilities in all of its key data-center locations in Europe, the United States, and the Asia-Pacific region. The idea is to provide electricity-guzzling data centers with round-the-clock clean energy, even when the sun isn’t shining or the wind isn’t blowing. The partnership with Energy Dome, announced in July, marked Google’s first investment in long-duration energy storage.
“We’ve been scanning the globe seeking different solutions,” says Ainhoa Anda, Google’s senior lead for energy strategy, in Paris. The challenge the tech giant has encountered is not only finding a long-duration storage option, but also one that works with the unique specs of every region. “So standardization is really important, and this is one of the aspects that we really like” about Energy Dome, she says. “They can really plug and play this.”
Google will prioritize placing the Energy Dome facilities where they’ll have the most impact on decarbonization and grid reliability, and where there’s a lot of renewable energy to store, Anda says. The facilities can be placed adjacent to Google’s data centers or elsewhere within the same grid. The companies did not disclose the terms of the deal.
Anda says Google expects to help the technology “reach a massive commercial stage.”
Getting creative with long-duration energy storage
All this excitement is based on Energy Dome’s one full-size, grid-connected plant in Ottana, Sardinia, which was completed in July. It was built to help solve one of the energy transition’s biggest challenges: the need for grid-scale storage that can provide power for more than 8 hours at a time. Called long-duration energy storage, or LDES in industry parlance, the concept is the key to maximizing the value of renewable energy.
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