Experimental and Numerical Investigation of a 4 MWh High Temperature Molten Salt Thermocline Storage System with Filler

Molten salt thermocline storage is a novel concept for storing large amounts of thermal energy at high temperatures of up to 560°C. Instead of storing molten salt in two separate tanks, as in the state-of-art systems, the density difference of hot and cold molten salt is used to maintain stratification inside a single-tank [1]. Advantages are cost savings due to the absence of the second tank, smaller ground coverage, no limitations in tank height due to short shafted pumps, also avoiding unused space at the bottom of the tanks and simplification of the gas handling. However, the greatest cost reduction potential arises from the application of a low cost filler material, substituting a large fraction of the costly molten salt. The total costs for the storage system can therefore be reduced significantly, Pacheco et al. [2] reported a cost reduction potential of 34% that can be increased to more than 50% if the entire storage volume could be utilized. For large scale applications, one challenge is to understand the scalability of this concept. Impacting factors are thermal strain in the tank walls and thermal ratcheting especially for large tank diameters and high temperature differences [2]. The dynamic temperature distribution in the storage is key to assess these issues. Therefore this study aims to investigate the thermocline filler concept both experimentally and numerically. [1] Gil A, Medrano M, Martorell I, Lázaro A, Dolado P, Zalba B, et al. State of the art on high temperature thermal energy storage for power generation. Part 1--Concepts, materials and modellization. Renewable and Sustainable Energy Reviews 2010;14:31–55. doi:10.1016/j.rser.2009.07.035. [2] Knödler, Philipp. Thermal Ratcheting in Thermocline Energy Storage Tanks: Parametrization and Application of a Continuum Model, Casablanca, Marokko: 2018