Sizing for survival: Building resilient off-grid LVDC PV-storage systems against long-return-period climate events

The increasing severity of extreme weather events demands enhanced resilience in off-grid photovoltaic and energy storage systems. This study aims to integrate quantitative risk analysis into the system sizing process to quantify and mitigate the probability of operational failure under long-return-period weather extremes, under the hypothesis that risk-based sizing can improve reliability without disproportionate cost escalation. A surrogate model is constructed from real and synthetic performance data to efficiently explore the design space and identify a Pareto frontier of robust system configurations. A Monte Carlo simulation is then applied to a case-study building in Bilbao, evaluating 100 candidate configurations against 100 bootstrapped weather patterns, representing 120 years of historical and projected climate data. The results show that fewer than 25% of the investigated systems maintain continuous operation under the most extreme conditions considered. The most cost-effective configuration achieving 100% reliability for a 100-year return period event combines an 80% oversized photovoltaic array with a 20% undersized storage system. These findings provide actionable sizing guidelines for resilient off-grid DC systems and underscore the significant economic trade-offs associated with designing for full climatic reliability in future applications and standards development.