Models based on too many parameters are complex and burdensome, difficult to be adopted as a tool for sizing these technologies, especially when the goal is not the improvement of electrochemical technology, but the study of the overall energy flows. The novelty of this work is to model an electrolysis hydrogen production process, with analysis and prevision of its electrical and thermal energy expenditure, focusing on the energy flows of the whole system. The paper additionally includes investigation on auxiliary power consumption and on thermal capacity and resistance as functions of the stack power. The electrolysis production phase is modeled, with a zero-dimensional, multi-physics and dynamic approach, both with alkaline and polymer membrane electrolyzers. Models are validated with experimental data, showing a good match with a root-mean-square percentage error under 0.10. Results are scaled-up for 180 kg/day of hydrogen, performing a comparison with both technologies. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.