A Reactor Train System for Efficient Solar Thermochemical Fuel Production¹

Thermochemical redox cycles are a promising route to producing solar fuels. In this work, a novel reactor train system (RTS) is proposed for the efficient conversion of solar thermal energy into 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 RTS overcomes technical challenges of high-temperature thermochemical reactors like solid conveying and sealing, while enabling continuous fuel production and efficient oxygen removal during metal oxide reduction. The RTS 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 counterflow radiative heat exchanger. The RTS can achieve heat recovery effectiveness of 80% for a train producing 100 kg-H₂/day with a 60 min cycle time. The RTS can take advantage of thermal energy storage to operate round-the-clock. Further, it implements waste heat recovery to capture the exothermic heat of water-splitting. If all auxiliary energy demands can be satisfied with such waste heat, the RTS base configuration achieves 30% heat-to-hydrogen conversion efficiency, which is more than four times that of current state-of-the-art thermochemical systems.