Designing cost-effective storage portfolios in decarbonizing power systems: a deficit stretch approach

High wind and solar penetrations would make bulk energy storage increasingly important for electricity system reliability. We introduce a deficit stretch framework that relates the temporal structure of generation shortfalls to optimal storage configurations in a decarbonizing grid and links the intensity, duration, and frequency of deficits to storage needs and cost–reliability trade-offs. Using Karnataka (India) as a case study, we simulate wind–solar–demand scenarios to examine (i) drivers of deficit-stretch emergence, (ii) which wind–solar–storage portfolios align with available storage technologies, and (iii) how these choices map onto Pareto frontiers of cost versus reliability. We cluster deficit stretches to identify characteristic storage durations (across hours to seasons) enabling a direct mapping from variability patterns to feasible technology options. Results indicate that solar share largely controls the deficit stretch duration spectrum. The proposed framework offers an empirical approach leading from analysis of renewables variability to consideration of bulk energy storage portfolios amidst cost–reliability tradeoffs and is extendable to other regions as well.