Experimental investigation on the thermal performance of a pilot-scale single-tank high-temperature molten salt sensible thermal energy storage system

Molten salt thermal energy storage (TES) has significant potential for solar thermal applications owing to its high operating temperature and excellent thermal stability. In this study, a pilot-scale single-tank sensible heat storage system employing molten salt is designed and constructed. The storage medium is the ternary nitrate Hitec (53 % KNO3 - 40 % NaNO2 - 7 % NaNO3), with a melting point of 142 °C. The heat transfer characteristics during charging and discharging processes, as well as during a 12-h static heat preservation period, are investigated. Furthermore, the effects of different water flow rates and outlet temperatures on the discharging performance are evaluated. Experimental results show that during charging, the system stores 749.66 MJ of thermal energy, with an average charging power of 62.47 kW and a storage efficiency of 89.25 %. During the 12-h static preservation stage, the temperature decreases by only 37.78 °C, resulting in a cumulative heat loss of 211.56 MJ, which demonstrates insulation performance superior to those of comparable systems. During discharging, increasing the outlet water temperature or flow rate substantially improves the average discharging power but simultaneously reduces the total energy released from the molten salt tank. Therefore, in practical applications, both parameters should be optimized jointly to achieve an optimal balance between the discharging rate and thermal energy utilization. The findings provide reliable experimental data to support structural optimization and the engineering application of single-tank shell-and-tube molten salt TES systems.