Impact of renewable energies to European energy systems under historical and future climate conditions

The development of the Earth's climate is expected to be one of the greatest threats to mankind and nature in the 21st century, with hardly predictable and perhaps irreversible consequences for future generations. Hence, it appears essential that societies worldwide try to tackle the emerging challenges with all possible means and need to undergo substantial changes, in particular, for resource management. Energy transition from fossil-based to renewable energies may play a major role contributing to climate change mitigation via drastic CO2 reductions. Here, a key is to better understand the variable renewable energies' (VRE) characteristics for present and future conditions, in order to strike a new path towards CO2-free energy systems and a more sustainable world. The emerging corresponding research field is highly complex and interdisciplinary. The Energy Transition and Climate Change project, hosted by the University of Cologne, aims to establish an interdisciplinary framework to tackle various research questions as well as to raise new ones. The present thesis is embedded in the project and benefits in particular from the exchange of knowledge between meteorology and economics. Three main studies are related to the project and are subject to this thesis, as well as in parts to publications. Study I aims to reduce the gap of available, reliable and comprehensive wind power data sets for follow-up investigations by generating a novel long-term European wind power time series based on a high resolution reanalysis by the German Weather Service (COSMO-REA6). Hereby, the improvement of a comprehensive understanding of the unique VRE power characteristics and their potential role for energy systems in Europe is supported. Analyzing this data base reveals strong variations in annual wind productions as well as of frequencies of extreme situations in Europe and Germany. In addition, results show high potentials of balancing effects within Europe and in particular for Germany, emphasizing the promising potential of VRE to help realizing the energy transition. Reanalyses products, such as COSMO-REA6, are often used as a meteorological basis for subsequent energy system studies including high shares of VRE. Since reanalyses contain considerable biases, the question of their impact to energy system models arises. Study II shows that energy conversion as well as energy system models are highly sensitive to initial errors associated with the meteorological input data, in particular under high shares of VRE. In this context, impacts on the overall composition of German electricity system as well as allocation effects of VRE capacities are observed. Such an uncertainty evaluation is a novelty in energy system modeling. Finally, Study III investigates the impact of climate change on a simplified European electricity system under strong decarbonization targets until the end of the 21st century. Here, the focus is on effects with respect to VRE technologies. For this purpose, simulations based on historical and future climate change scenarios, under strong CO2 emission assumptions, from the EURO-CORDEX project are compared. Simulations exhibit, that the system on the one hand adapts to climate change by pronounced shifts within VRE capacities and on the other hand by substantial local allocation adjustments, in order to fulfill the demand side while meeting the decarbonization target. The outcomes further show that, although European VRE potentials decline and their variability increases in the future climate change scenario, no substantial changes in the overall system (costs, ratio between VRE and non-VRE, electricity price) can be observed. This adaption strategy emphasizes the need for sufficient investments in transmission capacities, the urgency of a common and joint European approach and corresponding adequate actions from this day forward