The Impact of Transmission Development on a 100% Renewable Electricity Supply: A Spatial Case Study on the German Power System

In this paper, we analyze the interdependence between the structure of transmission infrastructure and the electricity mix, applied to the case of Germany today and into the future. In particular, we are interested in how an energy system based on a high share of distributed renewable sources operates under different transmission regimes, for example, copper plate or more constrained network topologies. We develop a stylized model of optimal generation and storage investment and operation, under different transmission expansion scenarios (current state, 2035 with and without HVDC lines, and copper plate). We take real data of the German electricity system, characterized by a particularly high share of distributed renewables, and select an extreme value for the future, that is, 100% renewable. Results suggest that the system can accommodate the high share of renewables, by installing a large amount of short-term and long-term storage capacities. Renewable electricity capacity investment is inversely related to the state of transmission expansion, and so is storage investment. The high level of granularity of the model also allows for a spatial allocation of renewable capacities, where wind is placed mainly in the north and solar PV rather in the south. The few cases of transmission congestion suggest that by expanding the grid modestly, a high share of renewable can be accommodated. The paper ends with a discussion of model constraints and further research ideas.