The system operates by using electrical energy to drive an air liquefier (effectively the charging system) and storing the resultant liquid air in an insulated tank (effectively the energy store) at atmospheric pressure.
When the stored energy is required, the liquid air is released from the storage tank, pumped in its liquid form to high pressure, vapourised and heated to ambient temperature (using either ambient heat or waste heat); the resultant high pressure gaseous air is used to drive an expansion turbine which in turn powers a generator (collectively the power recovery system). The exhaust is cold air.
As the cryogen is evaporated and returned to ambient temperature in the power recovery unit, we capture the cold exergy and store it. It is then used back into the liquefaction process. Harnessing and ‘recycling’ the cold broadly halves the energy cost of liquefaction, increasing the round-trip efficiency of the system to ~ 50%. This can be increased further by adding in waste heat, including low grade heat to the power recovery process.