Thermodynamic analysis of pump thermal energy storage system with different working fluid coupled biomass power plant

To investigate the criteria for selecting working fluids in biomass power plants coupled with pump thermal energy storage (PTES) system, two system models, HPO (heat pump only) and CP (complete PTES), were developed. Sensitivity analyses were conducted, and the performance of five commonly used working fluids was compared. The results show that the key factor for HPO is the coefficient of performance (COP) of the heat pump cycle, while for CP, the critical factor is the net power output of the thermal cycle. Roundtrip efficiency can be improved by reducing the compressor inlet temperature, minimizing the heat exchanger terminal temperature difference, and enhancing isentropic efficiency. HPO roundtrip efficiency increases with rising ambient temperatures, whereas CP roundtrip efficiency decreases. High isentropic indices and high, stable specific heat capacities are crucial criteria for selecting working fluids. Exergy analysis reveals that exergy losses primarily occur in turbomachinery for all working fluids. After parameter optimization, the highest roundtrip efficiencies for HPO and CP are achieved with carbon dioxide (54.35 %) and argon (61.01 %), respectively. Helium provides the lowest compressor and expander investment costs, at $50.86/kW for HPO and $142.23/kW for CP.