Adiabatic compressed air energy storage system and corresponding method

During operation of an adiabatic compressed air energy storage (ACAES) system (50), energy imbalances may arise between thermal energy storage (TES,60) in the (ACAES) system and the amount of thermal energy required to raise the temperature of a given volume of compressed air to a desired turbine entry temperature T i after the air has been discharged from compressed air storage (62) of the ACAES system (50). To at last partially redress such an energy imbalance it is proposed to selectively supply additional thermal energy to the given volume of compressed air after it has received thermal energy from the TES (60) and before it expands through the turbine (58). The additional thermal energy is supplied from a source external to the ACAES system, such as fuel burnt in a combustor (56). The amount of thermal energy added to the given volume of compressed air after it has received thermal energy from the TES is much smaller than the amount of useful work obtained from the given volume of compressed air by the turbine (58).