Enhancing the thermal stability of solar salt up to 600°C in extended lab-scale experiments

Abstract

Future trends push TES towards higher temperatures to increase solar-to-electricity conversion efficiency and novel storage materials are often considered the only viable option. To date these candidates suffer from either high costs (carbonate salts containing Li+) or severely attack structural materials (chloride salts) and are far from industrial implementation. An alternative approach is investigated in our work – the use of the classical Solar Salt with sophisticated gas management which selectively shifts the chemical equilibrium to the stable nitrate-side of the decomposition reaction. We demonstrate that the thermal stability of conventional Solar Salt (60-40wt % NaNO3-KNO3) is substantially increased when the storage system including the gas system is simply but effectively sealed. The key to this novel data is the unique feature of in-situ sample extraction and post-analysis that allows for a quasi in-situ determination of molten salt stability in terms of nitrite and oxide ion formation. Our investigations present clear evidence on the enhanced thermal stability at an experimental scale of about 100 g that is two magnitudes larger than conventional thermal analysis experiments.