Performance analysis of a novel semi-closed decoupled liquid air energy storage system integrated with vapor-injection heat pumps and refrigeration for micro-grid applications

Liquid air energy storage (LAES) systems utilize off-peak or renewable electricity to produce liquid air, which serves as a promising storage medium featuring high energy density, environmental friendliness and operational flexibility. Conventional coupled LAES systems rely on integration with industrial processes or external energy sources. However, the spatiotemporal mismatches between energy storage and electricity consumption necessitate advanced decoupled LAES configurations capable of efficient heat compensation and cryogenic energy recovery. To address this challenge, a novel decoupled semi-closed LAES system is proposed for micro-grid applications. The system integrates two vapor-injection heat pumps (VIHPs) and a vapor-injection refrigeration system (VIRS) to extract heat from ambient sources and recover cryogenic energy for air re-liquefaction, respectively. Comprehensive thermodynamic analyses and parameter optimizations are conducted to validate the performance improvement over a conventional decoupled LAES system. The results show that the integration of VIHPs and VIRS significantly enhances energy efficiency and reduces liquid air consumption. The proposed system achieves the optimal round-trip efficiency, combined cooling and power efficiency and specific liquid consumption of 28.18%, 54.35% and 7.96 kg/kWh. R1234ze(Z) is recommended as the optimal high-temperature refrigerant for heat supplementation, while replacing purified air with nitrogen as the storage medium can further improve the round-trip efficiency by 4.21%.