Simulation study on a novel solid-gas coupling hydrogen storage method for photovoltaic hydrogen production systems

Compressed hydrogen storage in photovoltaic hydrogen production systems faces several challenges, including limitations in storage volume, compression energy consumption and safety concerns. To improve the comprehensive hydrogen storage performance, this study develops a novel solid-gas coupling hydrogen storage method that combines metal hydride and phase change material (MH-PCM). Firstly, a vertical MH-PCM solid storage model considering the natural convection effect is proposed and investigated. Building upon this model, the solid-gas coupling hydrogen storage is constructed and integrated into the photovoltaic hydrogen production system to evaluate its comprehensive storage performance. Results reveal that considering natural convection leads to an approximately 12.7 % increase in the average storage rate, but is also accompanied by an uneven storage process. To address this unevenness and further enhance the storage rate, it's advisable to focus on structural optimization at the bottom of the tank. Additionally, improving the PCM thermal conductivity and hydrogen inlet pressure (to approximately 1 MPa) are also proven effective strategies. The proposed solid-gas coupling hydrogen storage demonstrates comprehensive advantages, particularly compact size and reduced energy consumption. Furthermore, appropriately increasing the coupling ratio between solid and gaseous capacities can achieve the even smaller storage volume. These findings can provide valuable theoretical and engineering guidance for implementing such hydrogen production and storage systems.