The increasing importance of flexible and large-scale green hydrogen production necessitates the accompanying modeling and simulation of these processes to optimize plant flexibility. State-of-the-art monolithic modeling approaches do not address the flexibility and interoperability expected from modular plants, as shown by (Mädler et al., 2022). Therefore, in this work, a new approach to the modeling of modular electrolyzers is proposed. Beginning with a steady-state equation system for the individual Process Equipment Assemblies (PEAs) it is later expanded to a detailed dynamic model. Instead of a single simulation flowsheet for the entire plant, this will result in a set of Functional Mockup Unit ready PEA models which can be combined depending on the plant assembly via co-simulation. This enables the user to generate models for various configurations and test the individual PEAs as well as the composite plant more efficiently. As a first step, a simple case study is presented where two steady state sub-models are developed and connected via co-simulation.