Solar and wind are now the cheapest and quickest-to-deploy sources of new electricity, but they are only as reliable as the weather. That intermittency is driving demand for long-duration storage that can bridge gaps between supply and demand. Energy Dome thinks compressed carbon dioxide can do the job more cheaply and more scalably than lithium-ion, and it has just switched on its first commercial plant in Sardinia, Italy.
How a CO2 battery actually works
The centerpiece of an Energy Dome plant is a huge white dome covering an area about the size of seven soccer fields, holding roughly 2,000 metric tons of carbon dioxide. When power is available, compressors squeeze the gas into a liquid stored in carbon-steel tanks. That compression generates heat, which the system captures in a proprietary thermal storage material. When the grid needs electricity, the carbon dioxide is released, warmed with the stored heat, and turned back into a gas that passes through a turbine. The gas then flows back into the dome, ready for the next cycle.
Why it matters for the grid
Compressed gas storage is not new; utilities have used compressed air in underground caverns for decades. Energy Dome's advantage is that it needs no specific geology, so it can scale more easily across different regions. Its first commercial plant in Sardinia, Italy, came online in 2025 with 200 megawatt-hours of capacity, enough to power about 18,000 Italian homes for 10 hours. The company says its technology is roughly 10% to 15% cheaper than lithium-ion for an eight-hour system, with better economics for longer durations up to 24 hours.
The trade-offs and what comes next
Energy Dome's roundtrip efficiency is about 70%, meaning it returns roughly 70% of the electricity it stores. Lithium-ion averages around 90%, though some iron-air batteries sit near 50%. The company also offers a version paired with natural gas turbines, which boosts efficiency but produces greenhouse-gas emissions. Energy Dome has a pipeline of about 30 gigawatt-hours of projects globally, and because it uses off-the-shelf components, it says the time from signed contract to delivered capacity is only two years. In June 2026 it signed a deal with Google for a 200 MWh plant in Ireland, expected online in 2028.
Key Takeaways
- Energy Dome uses compressed CO2 to store grid power for up to 24 hours.
- Its first commercial plant in Sardinia, Italy, has 200 MWh of capacity.
- The company claims a 10-15% cost advantage over lithium-ion for eight-hour storage.
- Roundtrip efficiency is about 70%, lower than lithium-ion's roughly 90%.
- A 30 GWh project pipeline is in the works, with a Google deal for Ireland due in 2028.
Source: MIT Tech Review • 🇺🇸 San Francisco
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