Solar Salt – Pushing an old material for energy storage to a new limit

[Display omitted] •Thermal stability limit of molten nitrate salts is enhanced from 560 °C to 600 °C.•Operation in a closed storage system increases thermal stability significantly.•Performance of Solar Salt is demonstrated in 100 g-scale.•Quasi-in situ sample analysis is used for proof of concept.•Formation of corrosive impurities is successfully suppressed at 600 °C. The implementation of inexpensive and reliable energy storage technologies is crucial for the decarbonisation of energy intensive industry branches and energy supply. Sensible thermal energy storage (TES) in molten salts is a key technology for storage of heat in the scale of gigawatt hours but currently limited to operating temperatures of 560 °C. Increasing the maximum operating temperature while maintaining thermal stability of the storage medium is one of the main challenges next-Generation TES systems are facing. Extending the upper temperature limit by only 40 °C increases the storage capacity by more than 16% allowing for more compact storage designs and cost savings in the $ million-range for large scale storage units. Here we propose a novel storage technology from a materials point of view that pushes the thermal stability limit of Solar Salt up to 600 °C by simply but effectively sealing the storage unit including the gas system. The concentration of the unstable nitrite ion and of the corrosive oxide ion could be reduced by 16% and 75%, respectively at 600 °C, compared to a salt system with open atmosphere. We present clear evidence of the enhanced thermal stability in long-term, 100 g-scale test campaigns at previously unequalled temperatures. These findings constitute a major advance in the design and engineering of next generation storage systems.