High temperature combined sensible-latent thermal energy storage

This work aims at proposing innovative Thermal Energy Storage (TES) systems for CSP power plants able to operate with high efficiency thermodynamic cycles working at 600°C. To do this, for CSP plants with gases or molten salts as Heat Transfer Fluid (HTF), high thermal capacity molten salts can be used in thermocline tanks with encapsulated Phase Change Material (PCM) top layer to limit the temperature degradation during discharge and thus increase the utilization rate of the storage system. Aluminum silicon (AlSi) has already been identified to have superior properties for a PCM: high specific energy density and volumetric heat of fusion, good thermal conductivity, low cost, and low environmental impact. A one dimensional dynamic model of combined sensible-latent TES system is presented, taking into account thermal transfer by conduction and convection in axial direction, measured thermo-physical properties for the storage media, and realistic heat losses to the environment. A prototype of molten salt single media thermocline tank is designed and modeled, and a parametric analysis is performed with different amounts of PCM for the same total tank volume. This numerical study shows that a combined sensible-latent molten salt thermocline concept with AlSi as PCM material can slow down the outlet temperature degradation during discharge and increase the storage capacity compared to a sensible only thermocline TES with the same tank volume.