Energy systems describe the techno-socio-economic interactions and relationships between the production, consumption, storage, transformation and distribution of energy in the different forms of electricity, heat and fuels. In this research area we focus on better understanding these energy systems. In particular, we investigate the impacts and interplay of different technologies (e.g. solar PV, electricity based mobility, hydrogen storage, etc.) with current and future energy systems and vice versa. Due to the different scales (buildings, districts, cities, regions, countries) of energy systems, we apply both top-down and bottom-up approaches. With a bottom-up approach we utilize our group’s expertise of district and building energy systems modelling, while for top-down approaches we rely on a large variety of data and models from other domains (meteorology, hydrology, economy, ecology, geography, sociology, etc.). Due to the high spatial and temporal complexity of the challenges in the energy systems, we apply tools from geographical information systems (GIS) along with data-driven (statistical & machine learning) and physical models.