Thermochemical redox cycles are a promising route for the production of solar fuels. In this paper we present a novel Reactor Train system for efficient conversion of solar thermal energy to hydrogen. This system is capable of recovering thermal energy from redox materials, which is necessary for achieving high efficiency, but has been difficult to realize in practice. The Reactor Train System overcomes technical challenges of high temperature thermochemical reactors like solid conveying and sealing, while enabling continuous, round-the-clock fuel production and incorporating efficient gas transfer processes and thermal energy storage.

The Reactor Train is comprised of several identical reactors arranged in a closed loop and cycling between reduction and oxidation steps. In between these steps, the reactors undergo solid heat recovery in a radiative counterflow heat exchanger. We report a heat recovery effectiveness of 75–82% with a train consisting of 56 reactors and a cycle time of 84 minutes. With ceria as the redox material, 23% of the high temperature thermal energy input is converted to hydrogen, while 49% is recovered as intermediate-temperature heat at 750 °C.

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