Proton exchange membrane (PEM) electrolysis technology appears as a key technology in the development of hydrogen-energy market applications such as energy storage or fuel for mobility. Its coupling with renewable electrical sources involves some issues related to the intermittent operation of PEM electrolysis systems. Within this framework, modelling is an essential tool to understand these issues, provide a thorough analysis and suggest some design optimization. A bibliographic analysis was carried out to identify existing models. State of the art highlighted that, although it is critical for the conception of such systems, only a few models take into account the dynamic of the whole system including balance of plant. Therefore, in this paper a new dynamic and multiphysic model of a proton exchange, membrane electrolysis system is presented. It was first developed under a graphical modelling formalism: the bond graphs (BG). Regarding dynamic and multiphysic modelling of complex systems, the BG have many advantages: it involves four levels of modelling using only one tool; it is a unified multiphysic approach; the parameters used have a physical meaning; the BG model can be refined very easily by adding new elements without having to start again the modelling process. Finally, because of its causal and structural properties, BG is suitable for modelling but also for control, sizing and diagnosis analysis. The model was then transcribed systematically into block diagrams in modular fashion for reutilisability of model libraries components. After a validation process, the model was proved to describe accurately the dynamic behaviour of a semi-industrial PEM electrolysis system (25 kW). The dynamic model can now be used to achieve some analyses through BG structural properties and simulations. Thus, it is a powerful tool to improve the design of PEM electrolysis systems powered by intermittent electrical sources. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.