Parabolic trough power systems that utilize concentrated solar energy to generate electricity are a proven technology. Industry and laboratory research efforts are now focusing on integration of thermal energy storage as a viable means to enhance dispatchability of concentrated solar energy. One option to significantly reduce costs is to use thermocline storage systems, low-cost filler materials as the primary thermal storage medium, and molten nitrate salts as the direct heat transfer fluid.

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... ior thermocline evaluations and thermal cycling tests at the Sandia National Laboratories' National Solar Thermal Test Facility identified quartzite rock and silica sand as potential filler materials. An expanded series of isothermal and thermal cycling experiments were planned and implemented to extend those studies in order to demonstrate the durability of these filler materials in molten nitrate salts over a range of operating temperatures for extended timeframes. Upon test completion, careful analyses of filler material samples, as well as the molten salt, were conducted to assess long-term durability and degradation mechanisms in these test conditions. Analysis results demonstrate that the quartzite rock and silica sand appear able to withstand the molten salt environment quite well. No significant deterioration that would impact the performance or operability of a thermocline thermal energy storage system was evident. Therefore, additional studies of the thermocline concept can continue armed with confidence that appropriate filler materials have been identified for the intended application. efforts at the Sandia National Solar Thermal Test Facility (NSTTF). Their continuing involvement and thoughtful reviews at the critical stages of the experimental program were appreciated. A sincere thanks goes to Bill Kolb of Sandia who developed the initial test plan and apparatus design for this experiment program. Key personnel at the NSTTF who designed, fabricated, instrumented, and helped monitor the test apparatus included Kye Chisman, John Kelton, Mike Edgar, Daniel Ray, and Blaine Emms; a special thanks for great work and support. Jim Moreno has since retired from Sandia, but the authors wish to acknowledge his expert consultation on some of the key issues we faced early in the testing effort. Bruce Kelly of Nexant also provided valuable expert consultation during early test planning. We would like to thank the team of experts at Sandia who provided dedicated analytical support in the face of other demanding priorities. Those personnel included