Thermodynamic performance analysis of multi-tank series/parallel packed bed thermal energy storage system with periodic charging cutoff temperature

As the demand for large-scale thermal energy storage systems in solar power generation and industrial waste heat recovery increase, molten salt packed-bed storage systems, known for their high energy density and thermal stability, have gained significant attention. Multi-tank packed-bed thermal storage systems provide a modular and scalable approach, ideal for applications with high thermal storage capacity demands. This paper establishes and validates a one-dimensional transient numerical model for a multi-tank series/parallel packed-bed molten salt storage system, examining the influence of charging/discharging cycles, the number of tanks, and heat transfer fluid mass flow rate on system performance. A periodic operation method that alters the charging cutoff temperature is proposed. The results indicate that at charge–discharge completion, thermocline layers exist only in the terminal tank of the series packed bed and are significantly thicker than in the parallel configuration; also, the series packed bed exhibits superior performance over the parallel type in both initial and steady-state cycles. Additionally, the operation mode that periodically raises the charging cutoff temperature to full charge can markedly enhance capacity ratio and utilization ratio (improvements of 6.47% and 8.25% for series and 8.29% and 10.50% for parallel), guaranteeing sustained high-efficiency and stable operation.