Experimental demonstration of a 5 kWth granular-flow reactor for solar thermochemical energy storage with aluminum-doped calcium manganite particles

A two-step cycle was considered for solar thermochemical energy storage based on aluminum-doped calcium manganite reduction/oxidation reactions for direct integration into Air Brayton cycles. The two steps encompassed (1) the storage of concentrated solar direct irradiation via the thermal reduction of aluminum-doped calcium manganite and (2) the delivery of heat to an Air-Brayton cycle via re-oxidation of oxygen-deficient aluminum-doped calcium manganite. The re-oxidized aluminum-doped calcium manganite was fed back to the first step to complete the cycle. A 5 kW(th) solar thermochemical reactor operating under vacuum was fabricated and tested to examine the first cycle reduction step. Reactor operating conditions and high-flux solar simulator control were tuned for continuous reactor operation with particle temperatures > 1073 K. Continuous operation was achieved using intermittent, dense granular flows. A maximum absorption efficiency of 64.7% was demonstrated, accounting for both sensible and chemical heat storage.