Thermal storage improves the dispatchability and marketability of parabolic trough power plants allowing them to produce electricity on demand independent of solar collection. One such thermal storage system, a thermocline, uses a single tank containing a fluid with a thermal gradient running vertically through the tank, where hotter fluid (lower density) is at the top of the tank and colder fluid is at the base of the tank. The thermal gradient separates the two temperature potentials. A low-cost filler material provides the bulk of the thermal capacitance of the thermal storage, prevents convective mixing, and reduces the amount of fluid required. In this paper, development of a thermocline system that uses molten-nitrate salt as the heat transfer fluid is described and compared to a two-tank molten salt system. Results of isothermal and thermal cycling tests on candidate materials and salt safety tests are presented as well as results from a small pilot-scale (2.3 MWh) thermocline.

McDonnell Douglas Astronautics Company, 1986, 10 MWe Solar Thermal Central Receiver Pilot Plant Mode 5 (Test 1150) and Mode 6 (Test 1160) Test Report, Sandia National Laboratories Report, SAND86-8175.
Faas, S. E., Thorne, L. R., Fuchs, E. A., and Gilbertsen, N. D., 1986, 10 MWe Solar Thermal Central Receiver Pilot Plant: Thermal Storage Subsystem Evaluation–Final Report, Sandia National Laboratories Report, SAND86-8212.
Solutia Technical Bulletin 7239115B, 1999, Therminol® VP-1, Vapor Phase/Liquid Phase Heat Transfer Fluid.
Nexant, LLC, 2000, Task 2 Report, Thermal Storage for Rankine Cycle Power Plants, NREL Task Order Authorization Number KAF-9-29765-09.
Pilkington, Solar International, 2000, Task 5: Annual Performance Simulation for ISCCS with Storage, NREL subcontractor AAR-9-29442-05 report.
Pacheco, J. E., and Gilbert, R., 1999, “Overview of Recent Results of the Solar Two Test and Evaluations Program,” Renewable and Advanced Energy Systems for the 21st Century, Proc. of the 1999 ASME Int. Solar Energy Conf., Maui, HI.
Price, H., and Kearney, D., 1999, Parabolic-Trough Technology Roadmap: A Pathway for Sustained Commercial Development and Deployment of Parabolic-Trough Technology, NREL/TP-550-24748, NREL, Golden, CO.
Burolla, V. P., and Bartel, J. J., 1979, The High Temperature Compatibility of Nitrate Salts, Granite Rock and Pelletized Iron Ore, Sandia National Laboratories Report, SAND79-8634.
Bradshaw, R. W., and Tyner, C. E. 1988, Chemical and Engineering Factors Affecting Solar Central Receiver Applications of Ternary Molten Salts, Sandia National Laboratories Report, SAND88-8686.
Martin Marietta, 1980, Molten Salt Safety Study, Sandia National Laboratories Report, SAND80-8179.
You do not currently have access to this content.