Dynamic thermodynamic performance analysis of a novel pumped thermal electricity storage (N-PTES) system coupled with liquid piston

Pumped thermal electricity storage (PTES) is considered as an innovative energy storage solution with advantages including high energy storage density and geographical independence. However, the current technology imposes stringent requirements on compressor performance, making it difficult to enhance the round-trip efficiency (RTE) and energy storage density. Hence, this study proposes a novel PTES system coupled with liquid piston. It can improve the quality of stored cold energy in the cold reservoir (CR), while simultaneously maximize the release of absorbed heat from the hot reservoir (HR) by liquid piston. By constructing a mathematical model for the entire system, this research delves into the underlying mechanism of the liquid piston's impact on the system, conducting a comprehensive analysis of its dynamic thermodynamic performance. The results show that the system achieves a RTE of 58.97 % and an energy storage density of 170.88 kWh/m3 under the design conditions. Compared to the conventional PTES system, the system exhibits an improvement of 2.5 % in RTE and 6.28 kWh/m3 in energy storage density. After the 15th cycle, the system attains a RTE of 70.42 %, representing an increase of 11.45 % compared to the initial cycle.