Grid-Scale Bubble Batteries Will Soon Be Everywhere

When the sun sets on solar panels, a gas‑filled dome rises to take its place, promising a new era of grid‑scale energy storage. The giant bubble on Sardinia holds 2,000 tonnes of carbon dioxide, not captured from factories nor drawn from the air but supplied by a gas company. Inside the dome, the CO₂ is permanently stored to absorb excess renewable power until it is required. Energy Dome, a Milan‑based company, calls this technology a “CO2 Battery” and has built a full‑scale plant in Ottana, Sardinia, finished in July. The plant compresses and expands CO₂ every day, spinning a turbine that delivers 200 megawatt‑hours of electricity or 20 MW over ten hours. By 2026, similar 5‑hectare installations will appear worldwide, each taking only half a day to inflate and younger than two years to construct. The first plant outside Sardinia will be built by India’s largest power firm, NTPC Limited, expected to finish at the Kudgi plant in Karnataka in 2026. In Wisconsin, Alliant Energy has permission to start a 2026 project that will power 18,000 homes. Google has committed to quickly deploy Energy Dome sites in its major data‑centre regions across Europe, the United States, and the Asia‑Pacific. The partnership, announced in July, marks 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. She notes that the challenge is finding storage that works for each region’s unique specifications, making standardization key. “They can really plug and play this,” Anda adds, highlighting Energy Dome’s modular approach. Google will target sites that offer the greatest decarbonisation impact and grid reliability, prioritising locations with abundant renewable output, says Anda. Terms of the deal remain undisclosed, but Google expects the technology to scale commercially. Energy Dome’s Sardinian plant was the first grid‑connected example, illustrating how to store more than eight hours of power, the industry calls long‑duration. When generation exceeds demand, the surplus is saved for later use, ensuring backup when wind or sun fails. Mainstream commercial batteries such as lithium‑ion offer only four to eight hours, insufficient for night‑time or multi‑day deficits. Other chemistries—sodium‑based, iron‑air, and vanadium redox flow—face obstacles of density, cost, degradation, and financing. Alternative ideas such as compressed air, heated sand, hydrogen, and underground water have yet to scale commercially. Pumped‑hydro can store gigawatt‑scale energy for days but requires rare topography, vast land, and up to a decade to build. CO₂ batteries need no special terrain, no critical minerals, and rely on existing supply chains, extending life to nearly three times lithium‑ion. Increasing scale cuts cost per kilowatt‑hour, and Energy Dome projects its system to be 30 % cheaper than lithium‑ion. China has announced plans for a CO₂‑based plant in Xinjiang, with reported capacities ranging from 100 MW to 1,000 MW. The Chinese entities are said to be fast and well funded, says Energy Dome’s founder, Claudio Spadacini. Visiting Sardinia in October, I saw a dome that had just been emptied, its interior collapsed, and the translucent outer shell glowing softly. “This is incredible,” I told Energy Dome’s global marketing and communications director Mario Torchio, and he replied, “It is. But it’s physics.” Tubes and pipes outside the dome move the gas for four key stages: compression, cooling, condensation to liquid, and storage in bus‑size vessels. The compressor raises pressure from one bar to fifty‑five bars within ten hours, after which a thermal system cools the CO₂ to ambient temperature. Sealed vessels hold the liquid, each about school‑bus size, and the whole cycle charges in roughly ten hours. During discharge, the liquid evaporates, heats, expands through a turbine, drives a synchronous generator, and returns gas to the dome for the next charge. Engineers inspect a dryer that keeps the gas dry at optimal moisture levels in the dome. Luigi Avantaggiato, an Energy Dome engineer, verifies the drying system that keeps the dome’s CO₂ dry. The dome size, roughly a sports stadium height at its apex, makes it visible and sometimes objectionable in rural areas. It can withstand winds of up to 160 km/h, but a two‑day advance warning allows operators to deflate and store CO₂ in tanks. A puncture would release 2,000 tonnes of CO₂, about fifteen round‑trip flights between New York and London on a Boeing 777, a figure far lower than a coal plant’s emissions. “It’s negligible compared to emissions of a coal plant,” Spadacini explains, adding that people must stay 70 m away until air clears. Despite risks, multiple giants—including Google, NTPC, and Alliant—are progressing towards commercial adoption, signalling a future where CO₂ fuels grid‑scale storage.