Advanced Heat Transfer and Thermal Storage Fluids

The design of the next generation solar parabolic trough systems for power production will require the development of new thermal energy storage options with improved economics or operational characteristics. Current heat transfer fluids such as VP-1™ which consist of a eutectic mixture of biphenyl and diphenyl oxide, allow a maximum operating temperature of ca. 300°C for a direct thermal storage system, At higher temperatures the vapor pressure would become too high and would require pressure rated tanks. The use of VP-1™ also suffers from a freezing point around 13°C that requires heating during cold periods. One of the goals for future trough systems is the use of heat transfer fluids that can act as thermal storage media and that are stable to around 425°C and have a freezing point near or below 0°C. This paper presents an outline of our latest approach towards the development of such thermal storage fluids.