Performance assessment of two-step solar thermochemical fuel production systems with a transient multi-scale model

Abstract

This study investigates the performance of solar thermochical hydrogen production systems across a range of operational conditions and material candidates. The objective is to guide the design of efficient reactor and enable rapid screening of promising redox materials. A multi-scale modeling framework is developed by integrating a system-level model, which includes heat exchangers and gas separation, with a detailed multi-physical model for a generic packed bed reactor. The transient multi-physical model incorporates fluid flow, heat transfer, mass transfer, and thermochemical reactions to enable more accurate performance predictions. Results show that solar irradiation direction perpendicular to the fluid flow minimizes temperature gradients, achieving a temperature difference as low as 49 K. A porosity of 0.75 results in the highest ${\eta }_{\text{STF}}$ and improving gas-phase heat recovery efficiency from 0.75 to 0.95 leads to an 18.9 % increase in ${\eta }_{\text{STF}}$. Under identical conditions, CeO₂ exhibited the highest hydrogen production at 3.8 mL/g, while Zr₁₅Ce_0.85O₂ produced 3.0 mL/g and La_0.6Ca_0.4Mn_0.6Al_0.4O₃ produced 1.3 mL/g due to slower oxidation kinetics. The transient model also predicts the reactor’s performance evolution over a 30-year operational cycle, considering optical and material degradation, enabling the assessment of long-term reliability and guiding future system designs. This study provides a comprehensive framework for reactor optimization, advancing the practical implementation and scalability of solar thermochemical fuel production technologies.