A solar receiver-storage modular cascade based on porous ceramic structures for hybrid sensible/thermochemical solar energy storage

Abstract

Abstract.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 receiverheat 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.

Performance of an Indirect Packed Bed Reactor for Chemical Energy Storage

“…Considering that r is the reaction rate, either for charging or discharging, calculated with the Shrinking core model [26]:…”

“…Currently, most works are related to the oxide/hydroxide systems, with direct and indirect heat exchange geometries including fluidized and packed beds [ 8 , 9 , 10 , 11 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. As far as oxide redox couples are concerned, structured fixed-bed systems are reported, based on cobalt oxides, perovskites and doped mixed oxides, and with direct contact between the TES and the HTF [ 16 , 25 , 26 , 27 , 28 , 29 ]. Although this configuration is advantageous concerning energy transfer efficiency, it presents limitations about the allowable HTF mass flow, which is related to the storage thermal power.…”

“…Considering that r is the reaction rate, either for charging or discharging, calculated with the Shrinking core model [ 26 ]: where rc is the extension of the reaction core (that is, R part – R c ) and it becomes equal to zero when the reaction is completed. is the oxygen partial pressure of HTF2, that is, on the powder side.…”

A Discussion of Possible Approaches to the Integration of Thermochemical Storage Systems in Concentrating Solar Power Plants

“…In the receiver the material is invested by the solar radiation, reacts and releases oxygen, regenerating the reduced chemical species, and is subsequently cooled and stored in a special tank. Several concepts of solid-material reactor [39,45], falling film reactor [46], fluidized bed reactor [47], swirl flow [48], etc., have been proposed in the literature, but the development of this component is still at an early stage due to the technological constraints associated with the direct irradiation (resistance of materials, quartz window sealing, differential expansion, and scalability). Depending on the type of receiver adopted, the reaction can occur under vacuum or in air flow, as shown in Figure 13.…”

A Moving Bed Reactor for Thermochemical Energy Storage Based on Metal Oxides

“…The concept of combined extraction of sensible and thermochemical energy has been also suggested for inert honeycomb structures coated with a thermochemical energy storage material [9] and for the oxidation of CoO and subsequent cooling in pressurized air [5]. Furthermore, a solar-driven cycle based on copper oxide was proposed, where sensible, latent, and thermochemical energy of the metal oxide is extracted for high-temperature power generation and oxygen production [10]. In general and almost independent from the concept, the metal-oxide particles should meet several criteria for long-term utilization in the suggested continuous concept: sufficient mechanical strength, resistance of particle stability towards chemical and thermal stress, adequate chemical reversibility of redox reaction, high reaction enthalpy and heat capacity for enhanced energy density, affordable raw material cost, and low environmental impact due to the open system concept.…”