Thermodynamic optimization of lithium chloride-potassium chloride-zinc chloride and lithium chloride-potassium chloride-magnesium chloride for thermal energy storage

Abstract

Electrical generators transducing and concentrating solar power to heat and then to electricity require a material with good thermophysical properties to store heat when there is no sunlight. Here, LiCl-KCl-ZnCl2 and LiCl-KCl-MgCl2 were observed for their capacity to store energy by the change in sensible heat content as a function of temperature. The ternary phase diagrams of the two salts were predicted using a thermodynamic model. Three eutectic points for LiCl-KCl-ZnCl2 and four eutectic points for LiCl-KCl-MgCl2 were predicted and experimentally verified. The heat capacity and thermal stability of the seven eutectic mixtures were measured to evaluate their heat storage capacity and operating temperature range. LiCl-KCl-ZnCl2 (13.86 % mol-40.63 % mol-45.51 % mol) and LiCl-KCl-MgCl2 (47.29 % mol-44.33 % mol-8.38 % mol) were found to be the best choices for heat storage materials, which have low melting points of 451.8 K and 612.8 K, large heat capacity of 1.25 J/g·K and 1.80 J/g·K, and wide operating temperature range from room temperature to higher than 823 K, respectively.