Evaluating the impact of cold leakage on liquid air energy storage: Advanced cold recharge strategies for actual applications

Abstract

Liquid air energy storage (LAES) offers high energy storage density and minimal geographical dependence, with the cold storage unit (CSU) serving as its core component. However, cold energy leakage from the CSU, due to the cryogenic operating conditions, reduces the system's round-trip efficiency. This study analyzes the losses caused by cold leakage and proposes three recharging schemes: direct liquid nitrogen recharging, indirect liquid nitrogen recharging, and liquid air pressure reduction recharging. Energy, exergy, and economic analyses were conducted, incorporating the impact of liquid nitrogen consumption and introducing a comprehensive efficiency metric. A 100 MW/800MWh LAES station model was developed to quantify the exergy destruction due to cold leakage, revealing a daily exergy loss of 3.17 MWh in the CSU. To mitigate this, the three recharging schemes were analyzed. In Case 1, direct liquid nitrogen injection into the tank resulted in a round-trip efficiency of 56.54 % and an exergy efficiency of 75.24 %. Case 2, which involved indirect liquid nitrogen recharging, slightly improved round-trip efficiency to 56.90 %, surpassing the ideal LAES efficiency of 56.62 %, with an exergy efficiency of 75.42 %. Case 3, using liquid air pressure reduction during discharge, resulted in a round-trip efficiency of 55.83 % and an exergy efficiency of 74.56 %. A comprehensive efficiency metric, considering liquid nitrogen consumption, yielded efficiencies of 56.08 % and 56.21 % for Case 1 and Case 2, respectively. The economic analysis indicated that cold leakage reduces the net present value (NPV) by 6.78 % and increases the levelized cost of storage (LCOS) by 1.40 %. Among the schemes, Case 2 was identified as the most optimal for LAES systems. Additionally, the chemical exergy of liquid air and returned air was calculated, demonstrating their substantial contribution to total system exergy. This study provides valuable insights for optimizing the design and operation of LAES systems, though further analysis of leakage based on specific tank parameters is necessary for accurate recharging scale assessment.