The European and International energy policy targets energy efficiency improvement and CO2reduction. Therefore, renewables are key players within our future energy supply system. In order to ensure security of energy supply and to avoid load peaks, highly interconnected power grids, also known as smart grids, have to deal with irregularities of phenomena such as sunlight, wind, tides and intelligently control these dynamic changes. Such a smart grid is denoted as a complex system. That is characterized by a large quantity of heterogeneous actors, collaborating within a dynamic and highly interconnected network. This results in big challenges in the steps planning, realizing and expanding such a system. These steps need to be based on a standardized description process to cope with the aforementioned challenges. In this paper, we combine the Smart Grid Architecture Model (SGAM) with the Use Case Methodology for describing processes in complex systems. Our new UC-SGAM Methodology exploits the benefits of both approaches and can also be applied to the Reference Architecture Model Industry 4.0 (RAMI4.0). The developed methodology is examined on two overload scenarios of the smart grid. It strongly enhances comparability and simplifies the visualization of complex use cases.