Exergy analysis and assessment of performance criteria for compressed air energy storage concepts

Compressed air energy storage (CAES) systems provide power reserve to compensate for intermittent renewable electric energy. The compressed air is stored to drive an open gas turbine. Enthalpy is close to zero at ambient air temperatures, which implies low storage efficiencies of the CAES open gas turbine cycle. Thus, in this project, the characterisation of CAES concepts based on exergy in contrast to enthalpy is discussed. The CAES energy efficiency defined as ηcaes = Wel,G / (Wel,M + Qfuel), resulting in approximately 42% for Huntorf and 54% for McIntosh, is unsuitable for characterizing CAES as an electrical energy storage. Instead, an alternative round trip energy efficiency ηrt4 is presented. An exergy-based counterpart is deemed ideal to evaluate storage properties of CAES. Calculations emphasize the efficient generation characteristics of fuel-driven CAES (e.g., McIntosh with 82% fuel efficiency of the turbine process as compared to a Carnot value of 75%).