Energy Dome has switched on its first commercial plant in Sardinia, Italy, and the company is betting that storing energy as compressed carbon dioxide will beat lithium-ion batteries on price for long-duration grid storage. The plant, which went live in 2025, holds 200 megawatt-hours of capacity — enough to power about 18,000 Italian homes for ten hours.
The startup’s approach is simple: when power is cheap and plentiful, compress carbon dioxide until it turns to liquid, then store it in tanks. When the grid needs power, release the gas, warm it with stored heat, and spin a turbine. The whole setup fits under a white dome about the size of seven soccer fields, holding roughly 2,000 metric tons of gas.
The Sardinia Plant
The plant in Sardinia is the proof point. Energy Dome turned it on in 2025, and it now serves as the working model for the company’s pitch. The facility stores 200 megawatt-hours of energy, which the company says can power about 18,000 Italian homes for ten hours.
The key component is the dome itself, which covers an area about the size of seven soccer fields and holds about 2,000 metric tons of carbon dioxide. Inside, compressors squeeze the gas into a liquid, a process that generates heat. That heat is captured in a proprietary thermal storage material, which holds it while the gas sits in tanks.
When the grid calls for power, the liquid carbon dioxide warms back into a gas, passes through a turbine, and flows back into the dome to start the cycle again.
Why Carbon Dioxide Beats Compressed Air
Compressed air storage has been around for decades. Utilities have used it in underground caverns to hold reserves, but that approach depends on specific geology — the caverns themselves have to exist naturally in the rock below. Energy Dome’s system needs no geology at all, which means it could be deployed almost anywhere.
That flexibility is the core of the company’s pitch. Where compressed air storage is limited to sites with suitable rock formations, Energy Dome’s tanks and compressors are standard equipment that can be assembled on almost any flat piece of land.
The Cost Comparison With Lithium-Ion
Lithium-ion batteries dominate short-duration storage today — systems that hold up to four hours of power. But the economics break down beyond that point. A lithium-ion system that provides eight hours of storage requires roughly double the number of cells, which pushes costs up sharply.
Energy Dome estimates that its technology is roughly 10% to 15% cheaper than lithium-ion batteries for an eight-hour system. The company says the economics improve further for longer durations — up to 24 hours — where its roundtrip efficiency stays steady while lithium-ion’s losses pile up.
The company’s plants that are either operational or under contract have eight or ten hours of capacity. That is the sweet spot for grid operators who want to smooth out daily peaks without building expensive, short-lived batteries.
The Efficiency Tradeoff
The tradeoff is real. Energy Dome’s process returns about 70% of the electricity it stores to the grid, a measure known as roundtrip efficiency. Lithium-ion batteries average roughly 90%, and some other long-duration storage techniques clock in lower — some iron-air batteries are around 50%.
But the comparison is not apples to apples. Lithium-ion is designed for fast response and frequent cycling; Energy Dome is designed for long duration. The two serve different purposes, and the efficiency gap reflects that.
The Natural Gas Version
Not all Energy Dome plants will be benign from a planet-warming perspective. The company offers a version of its system that pairs the carbon dioxide battery with natural gas turbines. In that setup, the internal heat storage is replaced with waste heat from the gas turbines, which helps the plant run more efficiently but ultimately results in greenhouse-gas emissions from the natural gas turbines.
That version is an option, not the default. The company has not said which of its planned projects will use it, and the Sardinia plant does not appear to be configured that way.
The Pipeline and the Timeline
Energy Dome has a pipeline of about 30 gigawatt-hours’ worth of plants in the works around the world. Many of these projects could come online by the end of the decade. Because the company uses off-the-shelf components, the time from a signed contract to delivered capacity is only two years.
In June 2026, Energy Dome signed a deal with Google to build a 200 MWh plant in Ireland, which is expected to come online in 2028. That timeline shows the company moving fast — a contract signed in mid-2026, a plant delivering power three years later.
| Project | Capacity | Status | Timeline |
|---|---|---|---|
| Sardinia, Italy | 200 MWh | Operational since 2025 | Already running |
| Ireland, for Google | 200 MWh | Under contract | Expected online in 2028 |
| Global pipeline | ~30 GWh | In development | Many by end of decade |
What Comes Next
Energy Dome will need to build many more projects to reach the 30 gigawatt-hours of storage it has planned across five continents. The company has only one commercial project currently operational, so the next few years will show whether the pipeline translates into working plants.
The company’s plans are ambitious, but the path from contract to delivery is relatively short — two years — which gives it a chance to scale quickly if the first plants perform as advertised.
The Bottom Line
Energy Dome is betting that cheap, standard equipment can beat lithium-ion on price for long-duration storage. The Sardinia plant proves the concept works. The pipeline shows the ambition.
The caveats are real. The technology is not as efficient as lithium-ion, and the natural gas version carries emissions. But the company’s position is strong: a proven design, a short timeline, and a target market — long-duration storage — where lithium-ion faces rising costs.
Whether the company can build enough plants to matter remains to be seen. But the first one is running, the second is under contract, and the math on cost is favorable. Energy Dome has a shot at becoming a meaningful player in grid storage, and the next few years will tell us whether it gets there.
Source material: “Energy Dome and its carbon dioxide batteries,” MIT Technology Review.
Get the Notebook.
The day's best stories and every fresh verdict, in plain English, in your inbox by seven. One email a day, no more.