THERMODYNAMIC ANALYSIS OF A NOVEL TRANSCRITICAL CO2 PUMPED THERMAL ENERGY STORAGE SYSTEM WITH A VORTEX TUBE DRIVEN BY PHOTOVOLTAIC THERMAL COLLECTOR

With the growing global emphasis on the utilization of renewable energy sources, the field of energy storage has garnered significant attention. Among the various storage technologies, Pumped Thermal Energy Storage (PTES) stands out as a highly adaptable solution that is not limited by geographical boundaries. This flexibility makes PTES an attractive option for a wide range of applications, as it can be implemented in diverse settings to support the integration of renewable energy into power systems. To enhance the roundtrip efficiency of PTES, this paper proposed a PTES system based on the transcritical CO2 cycle. Furthermore, the proposed system is combined with photovoltaic thermal (PVT) collectors to improve the coefficient of performance (COP) during the energy storage process by recovering the waste heat of PVT collectors. PVT can not only improve the power efficiency of photovoltaic, but also increase the inlet temperature of compressor to reduce the energy consumption. Considering the low critical temperature (about 31℃) of CO2, the vortex tube is utilized as a condensation equipment in the proposed system to condense CO2 to liquid under ambient conditions, so that the proposed system can be more flexible in the process of application. A computational framework is developed to examine the impact of parameters on thermodynamic performance. The sensitivity analysis of key parameters such as temperature of storage tank, turbine inlet pressure and vortex tube outlet pressure are carried out to determine the energy storage characteristics of the proposed system. In addition, multi-objective optimization is performed using a genetic algorithm to achieve the optimal design performances including round-trip efficiency and average electricity growth rate of PVT.