Thermodynamic Analysis of Counterflow Reactor Design and System Integration for Solar Thermochemical Hydrogen Production

Abstract

Solar thermochemical water splitting offers a promising pathway for sustainable hydrogen production by directly harnessing concentrated solar energy. However, achieving high system efficiency remains challenging due to reactor design limitations and thermal integration constraints. This dissertation introduces innovative thermal reduction reactor configurations featuring additional inlets and/or outlets to better approximate reversible, isothermal countercurrent solid-gas exchange. Computational analyses demonstrate that these configurations reduce entropy generation and thermal gradients, thereby improving thermodynamic reversibility and reaction efficiency. Building on this foundation, a comprehensive thermodynamic model of a two-step metal oxide redox cycle is developed, incorporating indirect solid-gas heat recovery. Results show that optimized heat recuperation enhances solar-to-fuel efficiency, and identifies optimal gas flow rates and redox temperatures that balance thermal losses and hydrogen yield. To enable continuous, round-the-clock operation, the system is further coupled with a high-temperature sensible thermal energy storage (TES) unit. A dynamic model simulating realistic solar input profiles confirms that appropriate TES sizing and integration strategy can maintain high system uptime and thermal stability. Overall, this work contributes a novel framework for improving the efficiency, operational flexibility, and practicality of solar thermochemical hydrogen production systems through advanced reactor design, heat recovery, and thermal storage integration.