The current energy transition towards a rising share of fluctuating and decentrally installed renewable power has introduced new challenges to the modelling of national and regional energy supply systems. More technologies are involved than in centrally designed energy systems, and the physical potential strongly depends on regional context factors. Furthermore, nontechnical factors such as social, economic, and legislative settings, may limit solutions that are technically feasible, and the

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... agement of multiple actors with varying interests at the local and national level is required. Empirical studies show the relevance of nontechnical factors, such as delays in the approval and installation of power plants, due to missing acceptance and knowledge [1] . Modelling and scenario analyses tools have a great potential to support such complex decision and management tasks. However, the available modelling and scenario analyses tools are mostly not suited to the needs of the local stakeholders managing the transition of their local energy system. The required simulation time horizon is in the range of decades due to the long planning, construction, and life times of the energy infrastructure, which hinders an intuitive understanding of the system. Additionally, the communication of models of this size and complexity is a barrier for the energy transition [1], as stakeholders in a decentrally organized energy system have very heterogeneous backgrounds, and cannot be expected to have a detailed system understanding. Current models of energy systems are bottom-up or hybrid models, thus often bound to the regions they have been developed for. A simulation model for the transition management of regional energy systems should cover the technical system within its socioeconomic and legal boundaries, and be accessible and comprehensible on the same time. This paper provides a detailed discussion of the available energy system models for Switzerland. Exemplary effects of social and legislative issues are demonstrated. We present the participative modelling environment TREES (Transition of Regional Energy Systems) that consists of a generic interdisciplinary model which is customizable to the specific application case.