*1.1. Background*

The energy transition towards a renewable energy system that serves the demands of the electricity, gas, heat, and transport sectors is one of the most complex societal projects of our time. The green transformation of all energy-dependent activities touches all individuals, all economic activities, and administrations worldwide. While the first steps have been taken, the local, regional, and national roadmaps for the future energy system, e.g., in 2050, remain a constant challenge and need permanent scientific assessments, course corrections, and refinements.
