Progress in optimizing thermal performance of nitrate salts and their mixtures for thermal energy storage

Nitrate molten salts, especially eutectic mixtures, are widely utilized in thermal energy storage (TES) systems due to their substantial energy storage capacity. However, the inherent shortcomings like the relatively high melting point for single nitrate salts, leakage during phase transition, and poor thermal conductivity hamper their widespread application. This paper provides a comprehensive summary of current research efforts on nitrate molten salts and their mixtures used in thermal energy storage. This review initially focuses on recent advancements in designing and developing novel multicomponent nitrate eutectic mixtures aimed at lower melting points. Subsequently, it explores ongoing efforts to enhance the thermal conductivity of nitrate molten salts. These strategies involve dispersing high thermal conductivity nanoparticles, incorporating porous supporting materials, and employing encapsulation techniques. Additionally, the study evaluates the application of Solar salt (60 % NaNO3-40%KNO3) and Hitec salt (7%NaNO3-40%NaNO2-53%KNO3) in concentrated solar power (CSP) plants, alongside their corrosion characteristics and the overall cost analysis of CSP facilities. Understanding these aspects not only helps optimize their performance but also encourages a thorough and comprehensive discussion of existing knowledge and promotes further advancements in the field.