Renewable energies are at the core of the social and political debates on the future of our energy supply system and current system security developments. How many new grid lines are necessary and why? What happens on windy days in the grid? How can system reliability be assured while integrating high shares of renewable energies? Will the new grid system be an extension of the actual or is it necessary to build a completely new one? What electricity transmission data can and should be disclosed to enable an integrative discussion on the future grid system?