Optimal utilization of renewable energy resources needs energy storage capability in integration with the electric grid. Ocean\ncompressed air energy storage (OCAES) can provide promising large-scale energy storage. In OCAES, energy is stored in the form\nof compressed air under the ocean. Underwater energy storage results in a constant-pressure storage system which has potential\nto show high efficiency compared to constant-volume energy storage. Various OCAES concepts, namely, diabatic, adiabatic, and\nisothermal OCAES, are possible based on the handling of heat in the system. These OCAES concepts are assessed using energy and\nexergy analysis in this paper. Roundtrip efficiency of liquid piston based OCAES is also investigated using an experimental liquid\npiston compressor. Further, the potential of improved efficiency of liquid piston based OCAES with use of various heat transfer\nenhancement techniques is investigated. Results show that adiabatic OCAES shows improved efficiency over diabatic OCAES by\nstoring thermal exergy in thermal energy storage and isothermal OCAES shows significantly higher efficiency over adiabatic and\ndiabatic OCAES. Liquid piston based OCAES is estimated to show roundtrip efficiency of about 45% and use of heat transfer\nenhancement in liquid piston has potential to improve roundtrip efficiency of liquid piston based OCAES up to 62%.
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