Inefficiencies in various components of the OCAES contribute to the loss of energy in the storage system.
Individual components in the OCAES system can be analyzed based on exergy analysis.
Energy efficiency and exergy efficiency of individual components in OCAES are discussed below.
In case of isothermal OCAES, liquid piston compressor efficiency is defined as the ratio of stored energy to work input.
In adiabatic OCAES, high-temperature high-pressure compressed air is passed through the TES to store thermal exergy of compressed air in the TES.
where [t.sub.0] is the operation time of the OCAES.
In the diabatic OCAES, external fuel is used to heat the air.
In case of isothermal OCAES using a liquid piston, liquid piston expansion efficiency ([[eta].sub.E]) for polytropic expansion index n is given by
Different types of OCAES systems are modeled based on energy and exergy analysis of individual components in the OCAES system.
Adiabatic and isothermal OCAES systems are considered without the use of fuel.
Those are listed in Tables 2, 3, and 4 for diabatic, adiabatic, and isothermal OCAES, respectively.
Figures 5, 6, and 7 show exergy flow in various OCAES configurations.