Transmission Grid Operation and Congestion Management in Future Renewable-Dominated Power Systems

The ongoing transformation of the European energy system, driven by ambitious decarbonization targets and the rapid expansion of renewable energy sources (RES), places increasing operational and structural stress on electrical transmission grids. Fluctuating generation patterns, declining dispatchable conventional capacity, and rising electricity demand exacerbate congestion, challenge security of supply, and increase reliance on costly redispatch measures. To address these issues, this thesis develops a comprehensive and highly customizable alternating current optimal power flow (AC-OPF) framework designed for large-scale, real-world power system simulations with a particular focus on congestion management. The model incorporates detailed representations of conventional grid components as well as flexible network elements such as Flexible AC Transmission Systems (FACTS), and supports both optimal dispatch and optimal redispatch calculations. Modules for simplified market simulation and expansion planning, time coupling dynamics for storage systems, detailed cost formulations, and interfaces to external models further extend the applicability of the framework. The model is evaluated on standard test systems and subsequently applied in two major case studies involving the German and European transmission networks for the period 2025–2050. The analyses are based on, and further develop, a comprehensive and high resolution data set of the European transmission system, ensuring a detailed and consistent representation of network topology and generation capacities. The results highlight substantial challenges for future system operation. In scenarios with high RES penetration, security of supply risks may arise during extended periods of low wind and solar availability, emphasizing the continued need for firm capacity and demand flexibility. Grid congestion in Germany is expected to intensify, particularly due to concentrated wind generation along the North and Baltic Sea coasts and limited north–south transfer capability. The analyses further show that high-voltage direct current corridors and cross border exchange are crucial for ensuring resource adequacy and reducing system costs. In addition, the deployment of FACTS devices appears to offer considerable potential to reduce redispatch volumes, associated costs, and occurrences of forced load shedding. For Germany, the simulations suggest that redispatch costs could be reduced by up to 30% by installing 40 FACTS devices. A comparison of market simulation outcomes with grid constrained optimal dispatch underscores that integrating network constraints earlier in the decision chain yields significant cost reductions, chiefly by improving the allocation of RES curtailment. Market‑based instruments such as bidding zone splits and dynamic, temporally and spatially differentiated grid fees further demonstrate the potential to reduce redispatch requirements, although they may introduce side effects such as influencing wholesale prices or creating distributional effects for plant operators. Overall, this thesis demonstrates that a combination of targeted grid reinforcement, flexible network elements, and market designs that internalize network constraints offers a credible pathway to reduce redispatch needs and system costs while maintaining security of supply in a European power system with a high share of renewable energy sources.