Development of a Molten-Salt Thermocline Thermal Storage System for Parabolic Trough Plants

TLDR

Thermal storage enhances the dispatchability and marketability of parabolic trough power plants by enabling on‑demand electricity generation, and a thermocline system achieves this with a single tank that creates a vertical thermal gradient separating high‑ and low‑temperature zones. The study develops a molten‑nitrate salt thermocline system and compares it to a conventional two‑tank molten salt system. The thermocline design employs a low‑cost filler material to supply most of the thermal capacitance, suppress convective mixing, and reduce fluid volume, while molten‑nitrate salt serves as the heat transfer fluid. Isothermal and thermal‑cycling tests on candidate materials and salt safety, together with data from a 2.3 MWh pilot‑scale thermocline, demonstrate the system’s performance and safety.

Abstract

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.