Dynamic and transient modelling of electrolysers by renewable energy sources and cost analysis of electrolytic hydrogen

Hydrogen energy sector has gained significant attention worldwide but one of the key enabling components for its success would be cheaper and sustainable hydrogen production. Hydrogen could be produced directly from natural gas or coal etc; alternatively it could be produced by electrolysis of water powered by renewable energy sources, nuclear energy or fossil fuel. Wind energy is growing rapidly, which can produce cheap hydrogen. Electrolysers can be employed to control the frequency of the electricity grid while also making fuel as a by-product. This thesis concerns the intricacies of hydrogen production by electrolysers from renewable energy sources. A generalised, input-based mathematical model of the electrolyser has been developed for various subsystems, such as current-voltage, Faraday efficiency, gas production, gas purity, differential pressure, temperature subsystem, parasitic losses, gas losses and efficiencies at various stages of operation. Some empirical equations have been developed and some adjusted parameters have been used in the model. The model has been tested and verified against the experimental measurements. A generic method has been developed for modelling the Faraday efficiency. Model simulations have been carried out to investigate the sensitivity of the results to the value of the capacitance and how this affects the dynamic response of the electrolyser. A new sizing method of the electrolyser has been developed for a stand-alone energy system such as the HARI project. The electrolyser model has also been simulated for maximum and efficient hydrogen production in a directly coupled mode of electrolysers with solar PV arrays without the maximum power point (MPP) tracker, which leads to an interesting finding that "electrolysers should not be operated at MPP". It has also been found that the dynamic and intermittent power supply from renewables can damage the stability of electrolysers and reduce the energy capture. This is especially true for pressurised electrolysers, which are favoured by the industry at present. The in-depth theoretical and practical analysis of several aspects confirms - contrary to industry trends - that "Pressurised electrolysers are less energy efficient, less durable, more costly and not adequately compatible for renewable energy powered operation, especially in the stand-alone energy systems, compared to atmospheric electrolysers".