Multi-decadal climate variability and capacity planning of off-grid hybrid renewable energy systems

Off-grid hybrid renewable energy systems are critical for decarbonizing remote regions, yet their long-term design is strongly shaped by climate-driven variability and change in wind and solar resources. This study investigates how multi-decadal weather variability shapes the optimal capacity mix and the trade-offs between cost, reliability, and emissions in an off-grid solar–wind–diesel–pumped-hydro system. Using 45 years of hourly meteorological data for an island power system, we perform multi-objective capacity optimisation under different curtailment constraints and storage capacities.

Results show that designs based on a single “typical” year systematically mis-estimate optimal sizing, especially for high-renewable, high-curtailment configurations. Across the 45-year ensemble, mean optimal capacities remain broadly stable but exhibit pronounced inter-annual deviations that intensify as curtailment limits are relaxed, with wind and solar capacities fluctuating much more than diesel backup. Relaxing curtailment simultaneously lowers levelised cost of electricity and carbon intensity by enabling higher variable renewable penetration, but with diminishing marginal benefits beyond moderate curtailment levels and storage sizes.

These findings demonstrate that capacity planning for off-grid hybrid systems cannot be decoupled from long-term climate variability. Robust, cost-effective decarbonisation requires multi-decadal resource assessment, explicit treatment of curtailment and storage design, and integrated techno-economic-environmental evaluation rather than single-year analyses. We explicitly compare single-year and multi-year designs to quantify these impacts and discuss implications for planning resilient low-carbon island and remote microgrids.