Efficiency enhancement of liquid air energy storage systems through ultra-high-temperature heat pump integration

Abstract

Liquid air energy storage is emerging as a promising technology for large-scale energy storage. It offers high energy density and geographical flexibility, making it an effective solution for grid peak shaving. However, the round-trip efficiency of standalone systems typically ranges from 50 % to 60 %, with insufficient utilization of compression heat being a key factor contributing to low efficiency. Enhancing the use of compression heat and increasing the reheat temperature during expansion are effective strategies for improving the performance of the system. This study proposes an innovative system that integrates an ultra-high-temperature heat pump unit with an organic Rankine cycle to address these challenges. The system leverages the ultra-high-temperature heat pump to upgrade compression heat, thereby raising the reheat temperature during the energy release phase and resolving the low reheat temperature issue common in traditional designs. Additionally, the organic Rankine cycle recovers and harnesses the waste heat from the compression process, generating additional power and improving the round-trip efficiency. A thermodynamic model was developed to design and optimize the system, achieving a round-trip efficiency of 63.14 %. Economic analysis further reveals that the dynamic payback period of the system is 6.82 years, with a net present value of 12.85 million USD over its operational lifespan, 2.13 times higher than that of standalone liquid air energy storage systems. These results demonstrate that the integrated system improves profitability and market competitiveness. By efficiently utilizing compression heat, the proposed system ensures safety, flexibility, and high efficiency, offering valuable insights for the development of large-scale standalone liquid air energy storage systems.