As the global energy transition accelerates, transitioning away from fossil fuels has become critical to assist the mitigation of climate change. Hydrogen, with its dual role as both an energy carrier and fuel, holds great potential for this transition. However, its large-scale production, particularly for industries like chemicals and transportation, still relies heavily on fossil fuels, posing a challenge for sustainable development.

This research focuses on advancing green hydrogen production, specifically through alkaline water electrolysis, a technology associated with zero greenhouse gas emissions. A key aspect of this work is addressing a gap in large-scale electrolysis modeling, with an emphasis on a modular system design. Modularity, as opposed to traditional single-unit scaling, offers improved operational flexibility and safety. This approach is especially relevant when electrolysis systems are powered by renewable energy sources, another critical component of the energy transition.

This thesis presents an investigation into the performance optimization of a modular alkaline water electrolysis system, designed to handle fluctuating renewable energy inputs. A physics-based numerical model was developed in Python, to simulate a large-scale AWE system composed of multiple modular units, capturing critical parameters such as temperature evolution, gas purity, and energy losses. The model was built progressively, starting from the cell level, incorporating a thermal model for temperature development and a mass transfer model for gas purity estimation. These combined elements formed a robust tool for simulating and optimizing the performance of modular electrolysis systems.

After validating the model against existing numerical and experimental data at the cell level, it demonstrated a strong ability to accurately capture the behavior of a single-cell system across all modeled parameters, including cell potential, temperature, and gas impurities. The differences between the simulated values and experimental data were minimal, further confirming the model's accuracy and reliability. This validation provided confidence in the model's predictive capabilities and laid the foundation for extending it for a larger modular system.

Following this, a scaling analysis was conducted to evaluate the model's performance when applied to a modular system. The simulations were carried out under both steady and varying power inputs, reflecting realistic operational conditions, particularly when coupled with renewable energy sources. The results highlighted the model's capacity to predict temperature evolution and gas impurity levels in such a scaled system. These findings indicated that the model not only captured the thermal and mass transfer behavior but also provided valuable insights into the effect of system scaling on overall performance and safety.

The outcomes of this research demonstrate that the developed model could act as a valuable tool for optimizing the performance of modular alkaline water electrolysis systems. The model successfully predicts the thermal behavior, gas purity, and energy losses across a range of operational conditions, including fluctuating power inputs typical of renewable energy sources. By enabling the fine-tuning of operational parameters prior to system deployment, this model provides a significant advantage in designing safe, efficient, and scalable hydrogen production systems. Future work could extend the model's capabilities by incorporating additional factors such as degradation mechanisms and detailed component-level interactions, ensuring even more robust predictions over long-term operation.

The utilization of water electrolysis for hydrogen production is expected to increase significantly in the upcoming decades. Modular system design offers great advantages for emerging markets, whilst providing the necessary flexibility in capacity that intermittent renewable energy sources require. Literature research reveals little information regarding modular water electrolysis systems. However, their availability on the consumer market proves that there is demand for such systems. To facilitate the emerging hydrogen market, a modular engineering design approach is used to develop a containerized alkaline water electrolysis system. This containerized system achieves a high degree of modularity by utilizing multiple modular sections. Each section functions as a stand-alone hydrogen production station, containing all necessary components required for safe hydrogen production. These components include heat exchangers, gas-liquid separators, modular alkaline electrolyzers, and a novel component called flow panels. In conjunction with the Dutch company XINTC, the design of the modular sections and their components is presented. Significant capital expenditure reduction is achieved by operating at atmospheric pressure, allowing for cost-efficient material selection and their corresponding manufacturing methods; both of which are discussed. Thermal, hydrodynamic, and particle dynamic models from literature are presented and evaluated. The proposed hydrogen separator is expected to achieve a separation efficiency of over 99.8%. A thermal system analysis concludes that the system is capable of operating at maximum capacity for ambient temperatures of up to 35 C. Additionally, a hydrodynamic system analysis shows that the pressure drop inside the system is dominated by that of the heat exchanger, and is in conformity with the Pressure Equipment Directive.

This study focuses on water electrolysis and aims to provide suggestions for the company XINTC Global, for the design of the electrolyser and the accompanying flow network. The most important parameters for this project are the dimensions of the cell, the geometry of the piping network, the electrode gap, the volumetric flow rate and circulation velocity. These parameters influence the performance of the cell. As a result, the production of hydrogen is optimized by fine-tuning these parameters. In addition, the performance in different electrolyser geometries is maximized assuming free circulation of the electrolyte. The geometries differ in the number of cells and the stacking arrangement and they are the single cell, single module and horizontally stacked geometries. The performance indicators are the flow velocity through the electrode gap and the volumetric velocity through the electrode gap, which is a product of the velocity, electrode gap and electrode depth. Furthermore, suggestions on the other dimensions are given, with the aim to maximize the flow rate or velocity. To study the behaviour of the electrolysis system, I developed a Python code that simulates the flow through the electrolysis cell and channel network. This numerical model is compared to an analytical model and experimental data from the literature. Finally, the simulations predicted that the optimum electrode gap width is dependent on the total number of cells. The results with the turbulent flow model, showed that the optimum electrode gaps were 1.85 mm 0.250 mm and 0.250 mm for a single module configuration with 1, 60, and 240 electrolysis cells, respectively. Moreover, the horizontal stacking arrangement of the modules, resulted in larger optimum electrode gaps, for the same number of cells.