Furthermore, a corresponding upper threshold is estimated to be around 40% for the share of intermittent generation capacity in both a 2030 and 2050 perspective (with 5% uncertainty). Beyond this share, costly additional preventive measures will have to be taken in order to guarantee power system stability. While these objectives do not yet have the force of law, they provide the basis for current discussions about the contours of the European electricity sector.5 Attaining the decarbonisation of the electricity sector with a majority of production stemming from intermittent renewables seems to pose very considerable technical and commercial challenges at the current state of technology as 100% of dispatchable back-up would frequently need to be mobilised in time frames of less than 24 hours.