Experimental performance evaluation of a laboratory-scale molten salt thermocline storage

Single-tank thermal storages, which are known from low-temperature systems, provide an opportunity for cost reduction in high temperature thermal energy storage systems. As for high-temperature systems limited experimental data is publicly available, a single-tank molten salt storage prototype was designed and built at Fraunhofer ISE. This paper covers an analysis based on test results addressing also quantitative energetic evaluation criteria, such as the theoretical and actual capacity of the storage, besides qualitative outcomes. The main aspect to be addressed in order to promote the application of thermocline systems is the quality of the stratification and the thermal efficiency of such a system. In this paper a method and the corresponding results are shown how to determine the thickness of the thermocline zone with finite temperature measurement positions. Also displayed are the inlet and outlet temperatures of the storage and the flow rate. During the conducted storage charging and discharging tests it can be seen that the storage outlet temperature remains constant for a long period of time, demonstrating a proper separation between cold and hot fluid.