Energy Dome CO2 Battery
The Energy Dome CO2 Battery is a long-duration mechanical storage system, not an electrochemical battery. It compresses CO2 into liquid using surplus renewable power, storing the heat, then evaporates and expands the gas through turbines to generate for 8-24 hours in a closed loop. CO2 liquefies under modest pressure, giving higher density than compressed air. Google made it the focus of its first long-duration storage investment in 2025.
The Energy Dome CO2 Battery is a mechanical, closed-loop storage system that despite its name is not an electrochemical cell; it belongs to the same family as Pumped-Storage Hydroelectricity and Compressed-Air Energy Storage. During charging it uses surplus renewable energy to compress carbon dioxide gas, storing the heat of adiabatic compression, and liquefies the CO2. During discharging the liquid CO2 is evaporated and expanded as pressurized gas through turbines to generate electricity, with the stored heat reused to drive the expansion, all in a closed loop. CO2 is useful because it liquefies under modest pressure at ambient temperature, giving notably higher energy density than ordinary compressed air. The system targets long-duration discharge of roughly 8 to 24 hours, addressing a gap left by the Lithium-Ion Battery, which is economic mainly for short durations of around four hours. That long discharge is attractive for backing AI and other data center loads that need constant power. Energy Dome's reference design is a 20 MW / 200 MWh unit with a claimed lifetime of more than 30 years, and the company has operated its technology in Italy for several years. In 2025 Google announced an equity investment and partnership with Energy Dome, its first move into long-duration energy storage, with plans to deploy CO2 Battery facilities at key data-center sites in Europe, the United States, and Asia-Pacific, aiming at 24/7 carbon-free operation. Specific projects in the pipeline include installations in Wisconsin (breaking ground in 2026) and at the Kudgi site in Karnataka, India. The naming is a useful illustration of how "battery" has become loose shorthand for any system that takes electricity in and gives it back later.