Ocean compressed air energy storage (OCAES) is a promising large-scale energy storage concept. Different types of OCAES viz. - Diabatic, adiabatic and isothermal are possible based on the handling of heat in the system. In diabatic OCAES, compressed air is cooled in a cooler and heated using external heat source before transport to the expander. In Adiabatic OCAES, heat from the compressed air is stored in a thermal energy storage (TES) and reused to reheat compressed air before sending it to the expander. In Isothermal OCAES, air is compressed and expanded isothermally which results in the least compression work and highest expansion work. These OCAES configurations are assessed using exergy analysis in this paper. The exergy efficiency of individual components, exergy flow and overall efficiencies of diabatic, adiabatic and isothermal OCAES are presented. Results show that adiabatic OCAES shows improved efficiency over diabatic OCAES by storing thermal exergy of compressed air in TES and isothermal OCAES shows significantly higher efficiency over adiabatic and diabatic OCAES.

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