A Solar Receiver-Storage Modular Cascade Based on Porous Ceramic Structures for Hybrid Sensible/Thermochemical Solar Energy Storage

The current state-of-the-art solar heat storage concept in air-operated Solar Tower Power Plants is to store the solar energy provided during on-sun operation as sensible heat in porous solid materials that operate as recuperators during off-sun operation. The technology is operationally simple; however its storage capacity is limited to 1.5 hours. An idea for extending this capacity is to render this storage concept from "purely" sensible to "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, or by manufacturing them entirely of such oxides. In this way solar heat produced during on-sun operation can be used (in addition to sensibly heating the porous solid) to power the endothermic reduction of the oxide from its state with the higher metal valence to that of the lower; the thermal energy can be entirely recovered by the reverse exothermic oxidation reaction (in addition to sensible heat) during off-sun operation. Such sensible and thermochemical storage concepts were tested on a solar-irradiated receiver-heat storage module cascade for the first time. Parametric studies performed so far involved the comparison of three different SiC-based receivers with respect to their capability of supplying solar-heated air at temperatures sufficient for the reduction of the oxides, the effect of air flow rate on the temperatures achieved within the storage module, as well as the comparison of different porous storage media made of cordierite with respect to their sensible storage capacity.