Impact of CO₃^2- impurities on the thermal performance of Solar Salt in thermal energy storage

Over the past decade, Solar Salt, composed of 60 % NaNO3 and 40 % KNO3, has emerged as the optimal material for thermal energy storage (TES) in concentrating solar power (CSP) plants. However, the successful commercial application of Solar Salt has necessitated the establishment and optimization of purity standards. The CO32- impurity has been overlooked in impurity studies of molten salts due to its relatively weak corrosive nature. However, this research reveals that the CO32 -impurity exerts a significant and non-negligible impact on the thermal performance of Solar Salt. This study investigates the influence of CO32 impurity in the range of 0.005 wt% to 0.5 wt% on the thermal-physical properties (liquidus temperature, density, viscosity) and thermal stability (weight loss, component analysis) of the most widely used commercial mixed molten salt, Solar Salt. The results demonstrate that exceeding the threshold of 0.01 wt% for CO32, the stability of Solar Salt at 565 degrees C decreases by >1 %, and the volatility of the system significantly increases. This research investigates the impact of CO32 impurities on the properties of Solar Salt and offers valuable insights and practical recommendations for optimizing the utilization of Solar Salt.