Molten chloride technology pathway to meet the U.S. DOE sunshot initiative with Gen3 CSP

Third-generation (Gen3) concentrating solar power (CSP) technologies require a thermally stable and inexpensive fluid to be used for heat transfer and thermal energy storage. For Gen3 CSP plants, a molten salt composed of MgCl2 – KCl – NaCl is a new candidate, but it is familiar enough to plants with existing molten-salt systems. To determine the best composition for the heat-transfer fluid, we mixed nine different ratios of the salts, dry/purified them following strict protocols, and tested them with a differential scanning calorimeter and a thermogravimetric analyzer. Our results showed that the lowest melting and solidification temperature of 385°C ± 1°C was determined for the eutectic composition 44.7 MgCl2 – 25.8 KCl – 29.4 NaCl (mol.%). We determined that improper handling and preparation of the salt mixture highly affects its thermal properties because of moisture absorption. Preparation standards—particularly the dehydration of hydrous MgCl2—merit further development.