Globally, all nations agreed to reach net-zero greenhouse gas emissions by 2050. This requires a drastic change in the energy system, including a shift towards intermittent renewable energies, the need for sector coupling, flexibility, and efficiency.

Flexibility and sector coupling are two concepts widely discussed in the literature, however, a common understanding is missing. In this report, we propose definitions and quantitative metrics for both concepts. Flexibility refers to managing the variations in energy supply and demand at different time scales. While sector coupling describes the interconnection of energy supply and demand sectors such as electricity, heat, gaseous fuels, liquid fuels, and solid fuels to shift loads across them.

The application of definitions and metrics are demonstrated for scenario assessment in Switzerland in the PATHFNDR project by using them as inputs or outputs of simulation models as well as policy and market analyses.