Hydrogen production performance optimization for direct-coupled photovoltaic electrolysis systems based on a novel 3D opto-electro-thermal model

Photovoltaic-powered electrolysis systems represent a promising approach for large-scale renewable energy storage, with direct-coupled systems offering particular advantages in terms of reduced system complexity and cost. However, a mismatch issue between photovoltaic (PV) and electrolysis (EC) modules of these systems could be caused by suboptimal structural design and flow rate control strategies, leading to a significant reduction in hydrogen production performance. While these problems could potentially be addressed through numerical simulation, existing low-dimension models are overly simplified due to the assumptions of spatial homogeneity, failing to adequately capture the intricate coupling mechanisms among optical, thermal, electrical and gas-liquid flow phenomena in these complex systems. In this study, a novel 3D opto-electro-thermal model has been developed for direct-coupled systems, utilizing semiconductor drift-diffusion equations and a gas-liquid two-phase flow model within each grid cell. This advanced model facilitates comprehensive performance assessments during the optimization of the fundamental system structure (PV-EC), including the evaluation of novel system configurations that integrate photovoltaic/thermal (PV/T) and contact-based thermal designs. Additionally, it could help to streamline flow rate control by optimizing the relative sizing between the membrane electrode assembly (MEA) of EC and PV modules. The results demonstrate that the PV/T-EC Non-thermal integration structure achieves the maximum Solar-to-Hydrogen efficiency (STH). Moreover, by setting the relative sizing at 2.25 %, maintaining the flow rate in a wide range without precise control could be sufficient to achieve outstanding and stable STH under real-world fluctuating conditions. This allows the flow rate control strategy to be effectively streamlined. The findings could provide guidance for optimizing hydrogen production performance by refining system structure and flow rate control strategy in direct-coupled photovoltaic electrolysis systems.