Abstract: A mixture of inorganic nitrate salts may include sodium nitrate and potassium nitrate in certain proportions which can be used both for the storage of thermal energy and as heat transfer fluid, for example within concentrated solar power (CSP) plants. Such mixture may be used, for example, in thermodynamic solar systems with point-focusing, receiver-type power towers using heliostat mirror geometries on-ground. As another example, the disclosed mixture may be used as heat transfer fluid in a number of applications for industrial processes involving heat exchanges in a wide range of temperatures. One example mixture is an anhydrous, binary salt mixture, comprising potassium nitrate KNO3 and sodium nitrate NaNO3 wherein the KNO3 content ranges from 60% by weight to 75% by weight, e.g., from 63% by weight to 70% by weight, e.g., from 65% by weight to 68% by weight.