Transient thermal behavior of alkaline electrolyzer with integrated waste heat recovery and thermal storage for sector coupling

The hydrogen industry is expanding rapidly due to the growing demand for clean fuels. However, enhancing energy efficiency is crucial to keeping technology costs competitive. This challenge is particularly significant for electrolysis, where a substantial portion of the electrical energy input is lost as heat because of overpotentials and irreversible processes within the electrolyzer. One promising approach is to recover and utilize the waste heat generated by electrolyzers to improve overall system performance. This paper presents a transient model developed in MATLAB's Simscape for a 2 MW alkaline electrolyzer integrated with a thermal storage tank and a district heating network, aimed at enhancing operational flexibility and energy efficiency. The unique contribution of this study lies in the application of a transient model capable of capturing and analyzing the thermal transient behavior of the system. This insight is essential for enabling effective sector coupling between the electrolyzer and the district heating network. One innovative aspect of this study is the comparison between non-stratified and stratified thermal storage tank models to investigate how thermal stratification affects storage performance. In general, the thermal storage tank increases heat utilization by storing excess thermal energy during periods when heat generation exceeds demand. This reduces thermal waste and improves the overall integration between the electrolyzer and the district heating network. Simulation results indicate that the electrolyzer operates at 80°C, while the district heating network requires a supply temperature of 70°C. The small temperature difference poses challenges for both heat transfer and thermal storage, limiting the useable temperature range of the thermal tank to 72–75°C. After 12 h of operation and consuming 24 MWh of electricity, the electrolyzer generates 4.4 MWh of recoverable heat, which is equivalent to 18% of the electricity used. A thermal storage tank with a capacity of 200 m 3 can store up to 25% of this heat. These results demonstrate that the proposed system can increase the overall efficiency of hydrogen production facilities by up to 18% compared to conventional hydrogen-only production through the recovery, storage, and utilization of waste heat in district heating applications.