Electrolysis systems are the key technology to produce hydrogen from renewable energy sources. The modeling and simulation of proton exchange membrane (PEM) electrolyzers and the connected power grid are a challenge due to highly fluctuating loads in the available electrical power. Our study focuses on the modeling of the electrolyzer and its balance of plant with varying loads resulting from different energy sources. The balance of plant contains a water supply system, the electrical power supply and processes for treating the produced hydrogen, in particular drying. The electrolyzer model is validated using steady-state and dynamic data from the literature. Thereby, it is shown that the developed model accurately represents the measurement results from the literature. Furthermore, we implement an empirical degradation model to assess the effects of different use-cases on the efficiency of the electrolyzer.