The archive · Climate & Energy · Strategic decision · 2020–2026
Energy Dome's CO2 Battery bet: first commercial 20 MW/200 MWh plant now live in Sardinia
Milan startup bets liquefied CO2 can store grid power for 10 hours; €40M Series B, first 20 MW/200 MWh plant running in Sardinia, Google invested.
Energy Dome
What the business is
Energy Dome builds 'CO2 Battery' plants that liquefy carbon dioxide under pressure and expand it through a turbine, discharging up to 10 hours of stored grid power.
Starting capital：About €54M raised by April 2023, including an $11M Series A (2021) and a €40M (~$44M) Series B; Google made an undisclosed strategic investment in 2025.
How it started
Milan engineer Claudio Spadacini — who had already founded geothermal company Exergy and biogas company Sebigas — launched Energy Dome in February 2020 with Dario Rizzi and Francesco Oppici. The idea was a closed-loop 'CO2 Battery': compress carbon dioxide into liquid, store it in an inflatable dome, then let it expand through a turbine to return electricity for hours, with no lithium or rare materials.
What happened
A demonstration plant at Ottana, Sardinia, started in 2022 and fed the Italian grid for more than three years. In April 2023 Energy Dome closed a €40M (~$44M) Series B co-led by Eni Next and Neva SGR, taking total funding to about €54M, with a claimed qualified pipeline above 9 GWh. In December 2024 ENGIE signed an offtake agreement for the full-scale plant, and the 20 MW/200 MWh unit — built on a remediated industrial site at Ottana — was commissioned in Q1 2025 and fully operational by July 2025, able to supply about 73 GWh a year to the grid. In August 2025 Google announced a strategic agreement and an undisclosed investment.
How it ended up
Still running and scaling: the Ottana plant operates as a grid-connected commercial asset with 10-hour discharge at 75% round-trip efficiency and won Best EU Project Under 100MW at the 2025 Energy Storage Awards. Construction of a facility in India started with commissioning targeted for H1 2026, a Wisconsin project with Alliant Energy was approved, and the global pipeline exceeded 10 GWh.
Background
Energy Dome is a Milan-based startup that stores grid electricity as pressurized, liquefied carbon dioxide. During charging, a compressor turns CO2 gas into liquid and stores it in an inflatable dome; during discharge, the liquid evaporates and expands through a turbine to drive a generator. The closed loop uses steel, water and CO2 — no lithium, no rare earths — and is designed for 8–24-hour discharge with a claimed 75% round-trip efficiency and a 30-year life.
Founded in February 2020 by Claudio Spadacini (who previously built geothermal and biogas companies Exergy and Sebigas), Energy Dome ran a demonstration plant at Ottana, Sardinia, that fed the Italian grid for more than three years from 2022. The startup raised an $11M Series A in 2021 and a €40M (~$44M) Series B in April 2023, bringing total funding to about €54M, and claimed a qualified pipeline above 9 GWh.
The bet was that grids would pay for 10-hour storage where lithium-ion is uneconomic. In December 2024 ENGIE signed an offtake agreement for the first full-scale plant; the 20 MW/200 MWh unit at Ottana was commissioned in Q1 2025 and fully operational by July 2025, able to supply about 73 GWh a year. Google signed a strategic agreement and invested in August 2025, and the company claimed a global pipeline above 10 GWh with construction started in India.
What has to be true
- Lithium-ion dominates 4-hour storage but gets exponentially more expensive at 8–24 hours; a CO2 plant's cost is mostly steel and compressors, so the unit economics invert at long durations.
- ENGIE signed an offtake agreement for the first commercial unit and Google made a strategic investment in 2025 — offtakers committed before the plant proved itself at full scale.
- The demonstration plant fed the Italian grid for more than three years, de-risking the technology before the commercial unit was built.
- The Ottana plant runs with 10-hour discharge at 75% round-trip efficiency and won Best EU Project Under 100MW at the 2025 Energy Storage Awards.
What can be applied
Prove a new storage chemistry where its physics wins — 10+ hours — instead of fighting lithium on 4-hour economics; a commercial lighthouse plant plus an offtaker turns demo credibility into pipeline.
Aftermath
As of November 2025 Energy Dome's first commercial CO2 Battery was operating at Ottana, Sardinia, as a grid-connected asset with 10-hour discharge, and the company was scaling: a facility in India was under construction with commissioning targeted for the first half of 2026, a project with Alliant Energy in Wisconsin had been approved, a national Italian pipeline of about 2 GWh was being developed, and the global pipeline exceeded 10 GWh. No revenue figures were public; the company remained private with Google as a strategic investor.
Sources
- Energy Dome Shines at the 2025 Energy Storage Awards
- Google invests in long-life batteries made in Italy
- Energy Dome gets $44M uplift into its CO2 battery for renewable energy storage
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