Criteria for performance improvement of a molten salt thermocline storage system

Thermal energy storage is considered to be an important subsystem for solar thermal power stations because of the fluctuations in sunshine over time. A molten salt thermal storage tank contains thermally stratified fluid, with hot temperature on the upper level and cold temperature in the lower level. Although a few studies have explored molten salt thermocline energy storage for solar thermal plants, the criteria for performance improvement are still not understood adequately. To this end, this paper summarizes four criteria for describing the performance of a molten salt thermocline energy storage system. The criteria emphasize different aspects of the storage process, including thermal storage capacity, entropy generation, efficiency η1 based on outlet temperature, and efficiency η2 based on thermocline thickness. The effects of the physical properties of different filler materials on the performance are also discussed. The findings indicate that filler particles with higher density, higher specific heat, lower diameter, lower thermal conductivity, and lower porosity should be selected to increase thermal storage capacity and efficiency. However, increasing the density and specific heat will also lead to higher entropy generation in the system.

► Four criteria for describing the performance of a molten salt thermocline thermal energy storage system are studied.
► The effects of the physical properties of different filler materials on performance are also discussed.
► Filler particles with a small diameter and low thermal conductivity can improve efficiency η1.
► Filler particles with large volume-specific heat capacity and small porosity can increase thermal storage capacity.