Influence of the heat capacity of the storage material on the efficiency of thermal regenerators in liquid air energy storage systems

Abstract

Abstract Liquid air energy storage is an innovative technology for electricity storage, using liquefied air as storage medium. Due to the high energy density of liquid air, the storage volume is smaller than that of similar storage technologies like compressed air or pumped hydro energy storage systems. Air is liquefied by means of a modified Claude-cycle. In the discharging process, liquid air is energy-efficiently compressed (compression of a liquid), vaporized, superheated, and finally expanded from high to ambient pressure using an air expander for power generation. In between, a thermal energy storage device at cryogenic temperature level is used to improve the round-trip efficiency of the system. One possible design is a packed bed thermal energy storage device, consisting of a cylinder and a packed bed of storage material. Investigations on thermodynamic properties show that especially the temperature-dependence of the heat capacity has a major influence on the performance of the thermal energy storage system. In this paper, nine real and further hypothetical storage materials are investigated. The influence of the heat capacity at cryogenic temperature is systematically analyzed and a general formulation in terms of summarizing key figures is developed. It turns out that especially the temperature-dependence is a significant parameter in this context, which is not considered within the majority of investigations in this field.