Investigation of a liquid air energy storage (LAES) system with different cryogenic heat storage devices

Liquid air energy storage (LAES) is a large-scale storage technology, which is using liquefied air as storage medium. Comparable to pumped hydro (PHES) and compressed air energy storage (CAES), LAES is charged with excess electricity from the grid and discharged, when the electricity demand is high. Working as a buffer for the electric grid, the availability and integrability of fluctuating renewable energy sources can be improved by LAES. In the charging process, ambient air is liquefied with an adopted Claude respectively Kapitza process. Compression heat is stored in a hot thermal energy storage device (HTES); a cold thermal energy storage device (CTES) is used as heat sink at cryogenic temperature to significantly improve the efficiency of the liquefaction. In the discharging process, liquid air is pressurized, heated up to ambient temperature by the CTES, superheated by the HTES, and expanded in an air expander for electricity generation. The CTES is used to recycle an exergy flow at cryogenic temperature from the discharging to the charging process. Since the round trip efficiency of the LAES strongly depends on this exergy flow, two different types of CTES are compared within this work. The liquid cold thermal energy storage device (LCTES) is based on a multi-tank storage system using propane and methanol, the direct cold thermal energy storage device (DCTES) is a packed bed storage system with direct contact between the fluid and the solid storage material. In this work, a comparison and an exergetic investigation of both systems is presented. The significant influence of the exergetic efficiency of the CTES and other technical aspects are worked out. Additionally, the influence of the pressure on the liquefaction and discharging process, and on the round trip efficiency is investigated. (C) 2019 The Authors. Published by Elsevier Ltd.