(a) Electricity storage energy capacity and (b) power capacity requirements as a function of variable renewable energy penetration. Capacity requirements are displayed relative to annual electricity or peak power demand respectively. Data based on a literature review of 30 studies modelling electricity storage requirements in low-carbon power systems in the US, Great Britain, Germany, and the EU.^{4,–6,9,–15,17,18,20,–31} Black lines show log-linear regressions and shaded areas the confidence intervals. Budischak scenarios: GIV—Grid-integrated vehicles, National Grid scenarios: CR—Community Renewables, TD—Two Degrees, SP—Slow Progress, CE—Consumer Evolution. Repenning scenarios: KS 80/95–80%/95% emission reduction.