Redox-oxide-based porous ceramics for efficient solar thermal energy conversion and storage

Abstract

Air-operated Concentrated Solar Power Tower plants store the solar energy provided during on-sun operation as sensible heat in porous solid materials that operate as recuperators during off-sun operation. This concept can be rendered to a “hybrid” sensible/thermochemical one via coating the porous heat exchange modules with oxides of multivalent metals for which their reduction/oxidation reactions are accompanied by significant heat effects (e.g. Co3O4/CoO, BaO2/BaO, Mn2O3/Mn3O4, CuO/Cu2O) or by manufacturing them entirely of such oxides. Based on the construction modularity of such systems, cascades of porous structures incorporating different redox oxide materials and distributed in a certain rational pattern in space tailored to the local temperature of the heat transfer medium have been tested to enhance its utilization and the storage of its enthalpy. Experiments with lab-scale ceramic honeycomb and foam cascades compared their sensible-only to the hybrid sensible/thermochemical capability as a function of redox material kind and loading, porous support employed, distribution along the reactor and air flow rate. The most promising configuration has been transferred to a solar-operated reactor. The experiments have shown that such an approach can maximize the amount of redox powder that can be thermochemically exploited efficiently in a given thermochemical reactor volume.