Energy, exergy, and economic analyses of a novel liquid air and pumped thermal combined energy storage system

Abstract

Liquid air energy storage (LAES) and pumped thermal energy storage (PTES) are geographically unconstrained and environmentally friendly, holding great potential for large-scale energy storage. The key similarity between LAES and PTES is that both systems require cold storage units, which typically use a flammable and explosive liquid-phase alkane medium or an inefficient solid-phase rock medium, posing challenges in terms of safety, environmental protection, and energy efficiency. This study presents a novel energy storage system that integrates LAES and PTES (PT-LAES), effectively eliminating the need for individual cold storage units. During the energy storage phase, the cold energy generated by PTES gas expansion is used for LAES air liquefaction, while during the energy release phase, the cold energy from LAES liquid air is utilized for PTES low-temperature compression. This paper investigates key parameters, including the effects of LAES and PTES unit charging and discharging pressures on system performance. Energy, exergy, and economic analyses of PT-LAES are also conducted. Results indicate that the proposed PT-LAES achieves an RTE of 56.57 % and the energy storage density of 167.53 $\mathrm{kWh}/m^3$. Compared to stand-alone systems, PT-LAES demonstrates better economics with a payback period of 7 years, an NPV of 187.2 million USD over 30 years, and an LCOE of 0.122 $\mathrm{USD}/kWh$.