Investigation of storage materials for packed bed cold storages in liquid air energy storage (LAES) systems

Liquid air energy storage (LAES) is a storage technology for electric energy, using liquefied air as storage medium. Balancing fluctuating power in- and outputs, storage systems improve the integrability and availability of renewable energies. Due to the high energy density of liquefied gases, the storage volume is small, especially compared to similar storage technologies as pumped hydro or compressed air energy storage. During the charging process, ambient air is liquefied with an adopted Claude-cycle using additional cold from a cold storage. When the electricity demand is high, liquid air is released from the storage tank for power generation in the discharging phase. Therefore, liquid air is pressurized with a cryo-pump, heated up in the cold storage and finally expanded using an air-expander. The cold storage is cooled down to cryogenic temperatures again. Transferring cold from the discharging to the charging phase, the cold storage is one of the key components, influencing the process efficiency of the LAES-sy stem. One option to design the cold storage is a packed bed cold storage (PBCS), which consists of a simple cylinder and a packed bed of storage material. Investigations on thermodynamic properties show that the temperature dependent heat capacity of the storage material has a major influence on the performance of the cold storage. The influence of different heat capacity characteristics on the performance of the PBCS is systematically analyzed. The resulting theory is applied to existing storage materials and their related heat capacities. Nine storage materials are investigated, ranging from metals to ceramics, minerals and plastics. (C) 2017 The Authors. Published by Elsevier Ltd.