Liquid CO₂

CO2 is stored in gas form in a dome. When charging, electricity is used to compress the CO2 into liquid form, which is stored in a pressurised vessel. When discharging, the liquid is heated up to turn it back into a gas, and as the CO2 expands from liquid to gas, it spins a turbine to generate electricity. It is similar to compressed air energy storage, which uses air instead of just CO2. However, because CO2 can be liquefied under pressure at 31°C, unlike most other gases, it allows larger amounts of energy to be stored in a relatively small pressure vessel and does not require specific geological reservoirs. The Italian company Energy Dome claims that its technology can charge and discharge with a round-trip efficiency of around 75%, storing power for around 10 hours.