Theoretical analysis on performance enhancement of stand-alone liquid air energy storage from perspective of energy storage and heat transfer

Liquid air energy storage (LAES) is a powerful technology for balancing power supply and demand for a low carbon network. However, its round trip efficiency is relatively lower compared with other large-scale energy storage technologies. In this paper, a stand-alone LAES is studied to provide guidelines for improving its round trip efficiency, from the perspective of energy storage and heat transfer. Storage exergy efficiencies of tanks (η_st) and heat transfer thermal efficiencies of heat exchangers (η_HE) are considered. Simulation results show that, among the storage tanks, the liquid air tank plays the most important role: when η_st increases from 0.7 to 1, η_RTE increases dramatically from 0.18 to 0.51; the M-cold tank determines if the stand-alone LAES could work. To improve η_st, first, good thermal insulation materials should cover the tanks; second, measures need to be taken to mitigate the mix of energy with different grades in the tanks, such as multi-stage energy storage; thirdly, reducing the number of tanks by looking for a liquid that has large temperature scales from-190 to 20°C. For the heat exchangers, η_HE of HE #2 has the most significant effect on η_RTE; for Cooler or Heater, η_HE does not affect η_RTE as η_HE is above 0.65, which indicates that almost 35% of the stored air compression heat is excess, which could be used for other purposes to improve the round trip efficiency.