Sector coupling for an integrated low-carbon energy transformation : a techno-economic introduction and application to Germany

While the first phase of the energiewende, focusing on the electricity sector, was largely successful, the second phase needs to focus on all energy usage, especially heat, transportation, and usage as a raw material in the chemical industry. In that context, intensified "sector coupling" will be required, accompanied by a further shift from fossil fuels to renewable ones. This chapter provides an overview of the upcoming challenges in the next phase of the energiewende, by focusing on the technical and economic challenges of coupling electricity, heat, and transportation, in an attempt to advance the low-carbon transformation. We apply the concepts to the ongoing energiewende in Germany. By intensifying the links between the sectors, one can harvest "low-hanging fruits" in terms of flexibility and fuel switching from fossil to renewable energies. This is a precondition to attain the ambitious targets of the energiewende with respect to CO2 emission reductions. While this chapter focusses on Germany, the technical and economic arguments are valid at a broader scale, and apply to other transformation processes as well. Section 9.2 describes the basic idea of "sector coupling", until recently a widely unknown concept, including a schematic stylized scheme. In Section 9.3 we describe how sector coupling might evolve in the transportation and heating sectors, and that far-reaching electrification is at the core of the process. Section 9.4 provides some concrete quantitative scenarios for sector coupling for the case of Germany to 2030 and to 2050, based on a rapidly growing body of recent literature. While there is consensus on the feasibility of reaching ambitious decarbonization targets, different models suggest different pathways of reaching them. The role of synthetic fuels (domestic and/or imported) is controversially discussed. Section 9.5 concludes.