Improving commercial-scale alkaline water electrolysis systems for fluctuating renewable energy: Unsteady-state thermodynamic analysis and optimization

Storing renewable electricity as hydrogen through water electrolysis is a pivotal strategy for achieving global energy transitions and net-zero emissions. However, the intermittency and fluctuation of renewable energy pose challenges on the operation of the water electrolysis systems, underscoring the need for in-depth analysis and optimization of their dynamic performance. This study evaluates the unsteady-state thermodynamic performance of a commercial-scale alkaline water electrolysis (ALK) system for integration with renewable energy sources. A mechanism-based model rooted in electrochemical principles and the laws of heat and mass transfer is firstly developed, which predicts the voltage and temperature within maximum discrepancies of 3 % and 5 %, respectively. The model is then employed to evaluate the dynamic performance of ALK under different system configurations, heat dissipation rates, startup frequencies and operation durations. Results reveal that integrating a heat storage tank and minimizing heat dissipation can reduce ALK's cold start-up time by 25 %, favoring the integration with renewable energy. Additionally, sustaining a high stack temperature of 365 K boosts the overall energy efficiency by 2.4 %, which can be achieved by using the model predictive control (MPC) method. These findings highlight the importance of thermal management and control optimization in improving the performance of large-scale ALK systems when driven by renewable energy sources.