A 2.5 MW/4 MWh demonstration system using novel energy storage technology based on a carbon dioxide battery is under construction in Sardinia, Italy, by Energy Dome. The CO₂ battery technology developed by the Milan-based company offers energy storage duration of 16+ hours and can be built using off-the-shelf components.

The system uses a closed loop thermodynamic process which can enable a high round-trip efficiency of 75% to 80%, according to the company. The gas is stored in a dome and is harnessed to charge a battery by condensing the CO₂ into a liquid at ambient temperature. Heat created by the compression process is stored in thermal energy storage systems, and the system then discharges by evaporating and expanding the CO₂ back into a gas.

The liquid CO₂ is evaporated with the assistance of the stored heat, and its expansion drives a set of turbines, generating electricity and feeding it back to the grid as the gas goes back into the bladder dome for use in the next charging cycle.

The CO₂ batteries can operate very quickly, absorbing and releasing energy nearly instantly and they are expected to be of value in smoothing out demand spikes or to stabilize a grid when bad weather disrupts generating systems.