A multi-level isobaric adiabatic compressed air energy storage system suited to part load operation

This paper proposes and evaluates an innovative multi-level isobaric adiabatic compressed air energy storage (MLIA-CAES) system suited to supporting the operation of a standalone energy system comprising both generation and consumption with little or no connection to an external electricity grid. The system aims to help reconcile the difference between the availability of renewable energy and load demand. In this system, pressurized air is stored at three distinct fixed pressures and each of three different compression/expansion stages uses at least two compressor/expander units of different powers to enable flexible operation. The system operation strategy ensures that each compressor/expander unit always works at or near its design condition. An operational strategy is proposed which minimizes the number of changes of operating mode. Using credible values for component efficiencies, the results show that when air pressures in three air/water tanks are 25 MPa, 3.97 MPa, and 0.63 MPa, respectively, the round-trip efficiency and the exergy efficiency can exceed 83 % during a given one-day working cycle if some reasonable allowance is made for the value of discarded heat and if losses in the electrical machines are ignored. •This paper proposes and evaluates an innovative multi-level isobaric adiabatic compressed air energy storage system.•With intermediate air receivers, mass flow rates may differ between stages.•An operation strategy is proposed to minimize the number of changes of operating mode.•The round-trip efficiency and the exergy efficiency can exceed 82 % during a given one-day working cycle.