Thermodynamic evaluation of a novel Rankine-based pumped thermal energy storage concept targeting thermal coordination and large temperature span

Rankine-based pumped thermal energy storage (PTES) is a potential electricity storage technology for accelerating the integration of renewables. This paper provides a novel Rankine-based PTES concept based on cascade-charging, dual-expansion, and hybrid thermal storage, which enables large temperature span and the cooperative thermal matching of the heat pump, thermal storage, and heat engine. A system layout and the corresponding theoretical model for energy and exergy analysis are developed. The integration of low-temperature heat is considered, and multiple criteria are defined to evaluate the thermal energy utilization quantitatively. Afterward, a systematic investigation into its performance is conducted. The influence of key parameters is analyzed with a multiobjective optimization to unveil the trade-off relations between different performance indicators. Beyond that, the exergy loss distribution of the presented concept is revealed, and a comparison with the traditional concept is also performed. Results show the concept has promising comprehensive performance. A round-trip efficiency of over 72 % is achieved under a 100 K temperature span with the exergy efficiency of heat engine reaching about 70 %. Moreover, the strong mutual promotion of thermal integration is observed. The concept reported here can offer a meaningful reference for the coordination design of the Rankine-based PTES.