Thermodynamic Steady-State Analysis and Comparison of Compressed Air Energy Storage (CAES) Concepts

Different compressed air energy storage (CAES) schemes - as options for large-scale energy storage - are compared through a thermodynamic steady-state analysis by determining the state variables based on irreversibility and real gas behaviour. Characteristic values (such as technical work, power and efficiency) of Huntorf and McIntosh plants as well as several advanced concepts under development (adiabatic, isobaric and quasi-isothermal CAES) are considered. The calculation methods are validated with a newly collected comprehensive set of measured operational data of the reference plant Huntorf making this review unique and novel. It is found that in the existing CAES plants the largest energy loss occurs during compression by inter-cooling the compressed air (around 95 %). Thus, to enhance energy storage efficiency adiabatic and isothermal concepts are encouraged since they can lead to significantly higher values. The ambiguous energy storage efficiency of CAES is discussed in detail. The turbine conversion coefficient which in conventional gas turbines usually does not exceed 45 % or 60 % in combined cycle power plants respectively can reach in CAES turbines more than 80 %.