In the coming years, energy storage will be the sector where technological competition for energy transition intensifies the most.

To date, aside from traditional hydroelectric pumping, the sector seems largely dominated by lithium batteries, although alternative solutions are also gaining traction. These include lithium-free batteries, CAES (compressed air energy storage systems), gravity systems, thermal and liquid air storage, and iron batteries.
One variation of CAES – systems where excess renewable energy is used to compress a gas, store it, and then, when needed, use the compressed gas to drive a turbine connected to an alternator – uses CO2 instead of air.

But why CO2, specifically?

• It is one of the few gases that can transition from the gas state to the liquid state at room temperature and pressures that are not too high;
• it is a natural and very common gas, emitted by sources such as soil in geothermal areas;
• it is cheap and unreactive, and storing it as a gas at room pressure is neither difficult nor expensive.