Elaboration of Conductive Thermal Storage Composites Made of Phase Change Materials and Graphite for Solar Plant

Abstract

New thermal storage composites made of graphite and PCM (NaNO3∕KNO3 eutectic) have been developed for solar thermal power plants using direct solar steam generation. Those materials, obtained using different elaboration routes (compounding, infiltration, cold compression) and graphite types, are presented with their respective properties (enhanced thermal conductivities, thermal storage capacities, stability) and compared together. Both the laboratory and industrial scales and grades are considered and compared. The infiltration route has been found to be inefficient before the two other ones. Compound composites present isotropic properties and thermal conductivity intensification in the medium range (a factor of 10 for 7wt% in graphite). Cold compressed composites present highly anisotropic properties and strong intensification in thermal conductivity (a factor of 31 at 200°C for 20wt% in graphite). Their melting and solidification temperatures as well as their intrinsic storage capacity are close to the pure salt ones.