Demonstration of Multiyear Solar Thermochemical Energy Storage via the Cobalt Oxide Cycle

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Conference Proceeding

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We present a proof of concept demonstration of solar thermochemical energy storage on a multiple year time scale. We designed and fabricated a 4-kW solar rotary drum reactor to carry out the solar-driven charging step of solar thermochemical storage via metal oxide reduction-oxidation cycles. During the summer of 2019, the solar reactor was operated in the Valparaiso University solar furnace to effect the reduction of submillimeter cobalt oxide particles in air at approximately 1000°C. A particle collection system cooled the reduced particles rapidly enough to maintain conversions exceeding 84% for feed rates of 2.9-60.8 g/min. The solar to chemical storage efficiency, defined as the enthalpy of the reduction reaction at 1000°C divided by the solar energy input, reached 20% for an input solar flux of 1400 kW / m2 and a cobalt oxide feed rate of 60.8 g/min. Samples of the reduced cobalt oxide particles were stored in vials in air at room temperature for more than three years. The stored solar energy was released by reoxidizing samples in air in a benchtop reactor. Measurements of the oxygen uptake by the reduced metal oxide confirm its promise as a medium to store and dispatch solar energy over long durations.

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