Thermodynamic analysis of novel one-tank liquid gas energy storage system based on ammonia-water mixture fluid

Given the growing focus on energy storage systems, liquid gas energy storage (LGES), which is globally applicable, is being rapidly developed. However, the liquefaction issue of efficiently liquefying the working fluid within LGES remains a significant constraint on its development. In this study, the ammonia-water mixture is used as the working fluid in LGES to address the liquefaction issue, and the number of storage tanks is reduced to one to improve the energy density. Two different one-tank liquid ammonia-water mixture energy storage systems (one-tank LAWES) are proposed and compared. Configuration 1# (C1) features a simple condenser, whereas configuration 2# (C2) incorporates a modified liquefaction process that is similar to some LGES systems. The energy and exergy performances of these two configurations are evaluated and compared. The parametric sensitivity analysis is conducted, and the relationship between the one-tank LGES and Carnot Battery is discussed. The results show that C1 with a simple condenser has better performance, and its roundtrip efficiency and energy density under baseline condition are 48.65 % and 55.03 kWh∙m⁻³, respectively. Moreover, based on the exergy analysis, thermal energy storage unit 2 is the first priority for improvement in both configurations. The ammonia concentration of the fluid in the storage tank has a slightly positive effect on the roundtrip efficiency of C2, whereas it has a slightly negative effect on the roundtrip efficiency of C1. The one-tank LGES is a Carnot Battery because electricity is stored as thermal exergy rather than mechanical energy.