Influence of fillers on performance of molten salt thermocline storage

For the energy transition large scale electrical energy storages are needed for grid balancing. Therefore, Carnot Batteries might be one economic solution. The central component of such systems is a high temperature thermal energy storage, which must be of low cost to be competitive with other storage technologies. Molten salt storages are often discussed in this context and many authors propose the use of single tank systems with the use of low-cost filler material to further decrease the investment cost. For single tank systems with filler materials one important parameter is the void fraction, as it is known that the stratification and with this the exergetic efficiency is dependent on it. This means that the choice of fillers has an influence on the LCOE of the entire system. It had been previously observed in simulations and experiments in a 300 l water tank, that the stratification was better without the use of fillers. Fig.1. is showing the spreading of the thermocline in the packed bed zone during a charge with and without filler from initially homogeneous temperatures inside the storage. Similar experiments were performed in a molten salt facility and a 900 l prototype with solar salt only in the one case and with an introduced ceramic filler in another case. Key performance indicators for both setups are going to be presented.