cells is achieved with randomly textured superstrates (TCO and/or glass). Due to a continuous and broad variation of occurring structure sizes in such textures, their optical simulation is challenging. In this paper we introduce an approach to establish a methodology for 3D optical simulation of silicon thin-film solar cells on randomly textured superstrates. The approach includes three steps. In a first step a fabricated structure is analysed to identify its typical geometric features. In a second step the single geometrical features are optically simulated using the rigorous coupled wave analysis (RCWA). The third step includes an investigation of how the results of the single features can be combined to describe the optical characteristics of the complete random structure. In this paper we concentrate on the first two steps. We introduce the analysis of an exemplary superstrate structure and investigate the optical properties of the single structure features. Preliminary results of this investigation are shown and a proposition of how to optimise the structure geometry is presented.