ABSTRACT
Efficient utilization of renewable but intermittent energy sources such as solar, wind and geothermal for electrical power production is dependent on energy storage technologies. Among these technologies, CAES technology is of particular interest due to its high reliability, economic feasibility, and minor environmental impact. Large-scale CAES systems such as the ones in Huntdorf, Germany (290 MW) and McIntosh, Alabama (110 MW) are already running and use underground caverns for compressed air storage. In such systems, typically, turbo machinery is employed and natural gas or other fuels are used during the compression and expansion phase of the compressed air. Excepting large-scale CAES systems, micro-scale distributed CAES systems is proposed to be used in conjunction with off-grid stand-alone photo-voltaic panels or wind turbine units in order to minimize the dependency on centralized power system grids. Lemofouet (2006) presented a detailed discussion on the feasibility of various CAES systems can be found. Grazzini & Milazzo (2012) and Hartmann et al. (2012) analyzed efficiencies of several adiabatic CAES configurations with the help of an energy balance. Isothermal CAES can also minimize the energy loss that occurs during the charging and discharging processes by minimizing the temperature difference of the air with the environment (Eckard, 2010). Micro-CAES with an air cycle heating and cooling system can use the heat of compression and the cooling effect of expanding
(charging) and a discharge phase. The ability to efficiently store and discharge energy of CAES systems depends critically on the initial and final storage volumes, operating thermodynamic conditions (pressure, temperature), as well as the rate of compression and discharge and intermediate exchange capabilities. During the compression phase, the rate of compression and the quality of intermediate heat exchange determines the temperature of the system, and any heat irreversibly lost adversely affects the efficiency of the system. During discharge, the compressed air (or gas) is expanded and the discharging process will be investigated in detail according to energy balance theory in the future.
