Trendlines for flexibility power capacity requirements relative to peak power demand as a function of wind, solar and nuclear power penetration for the GB power system. Trendlines in (a) are given for data series with more than two data points and coefficient of determination of R2 ≥ 0.85. Trendline formulas are rearranged so the negative offset gives the x-axis intercept (i.e. the share of capacity above which flexibility is needed). Bulk generation capacity consists of wind, solar, nuclear, coal, gas (combined cycle), biomass, geothermal, waste, and wave. Flexibility capacity consists of electricity storage, interconnectors, demand-side response, gas (open cycle), hydropower, oil, and diesel. Grouping used in (b): Industry and Government: BEIS (2018), BNEF (2018), Carbon Trust (2016), CCC (2015), National Grid (2018). Academia: Heuberger et al. (2018), Pfenninger et al. (2015), Price et al. (2018), Zeyringer et al. (2018).
