Co-optimizing transmission and active distribution grids to assess demand-side flexibilities of a carbon-neutral German energy system.

In modern power system planning and operation, the relevance of distributed power generation units and demand-side flexibility options grows. As a consequence, smart planning and operation routines become necessary also in the distribution grid. We therefore develop a co-optimization framework to consider transmission and distribution system constraints and their interactions together. This enables bidirectional flows between both systems, supporting a consistent and cost-efficient overall energy system. The key feature of this paper is an automated coupling of two independently and modularly defined systems. It allows a bottom-up modelling approach of energy demands, conversion and storage technologies from both system levels. However, this approach increases the model size significantly. Thus, timeseries aggregation methods are applied to reduce the computational complexity. The results for the optimal planning of the coupled German energy system show that the electrification of heat and mobility sectors in the distribution grid is not only beneficial to achieve carbon neutrality in 2050, but also to particularly make use of additional flexibility potentials. Our results underline a significant positive correlation between a smart operation of heat pumps and charging stations with the maximum integrable capacities of low-cost rooftop photovoltaics in the distribution system. • Open-source framework to couple transmission system and active distribution grids. • Co-optimization of both system levels enables a holistic model with a global optimum. • Case study: German energy system with the carbon-neutrality target by 2050. • Electrification of residential heat and mobility sector to unlock flexibilities. • Gained flexibilities promote 20% higher PV capacities and reduce system costs by 7%. [ABSTRACT FROM AUTHOR]