Using molten salt at a solar field and in a TES system eliminates the need for expensive heat exchangers. This concept allows a solar field to operate at higher temperatures than systems using other common heat transfer fluids such as oils. Due to the elimination of heat exchangers and the reduction of heat transfer fluids, the use of molten salt as a heat transfer fluid substantially reduces the total cost of a TES system.
Unfortunately, molten salts freeze at relatively high temperatures—about 120 to 220°C (250 to 430°F). This means that special care must be taken to ensure that the salt does not freeze in the solar field piping. The Italian research laboratory, ENEA, and Sandia National Laboratories in the United States are currently developing new salt mixtures with the potential for freeze points below 100°C (212°F) to make molten salt much more manageable as a heat transfer fluid.
