Designing a sector-coupled European energy system robust to 60 years of historical weather data.

As energy systems transform to rely on renewable energy and electrification to mitigate climate change, they encounter stronger year-to-year variability in energy supply and demand. Yet, most infrastructure planning relies on a single weather year, risking a potential lack of robustness. In this paper, we optimize capacity layouts for a European energy system under net-zero CO emissions for 62 different weather years. Subsequently, we fix the layouts and optimize their operation in every other weather year to assess resource adequacy and CO emissions. Our analysis shows a variation of  ± 10% in total system costs across weather years. Layouts designed for years with compound weather events prove more robust, achieving resource adequacy of 99.9% and net-negative CO emissions of -0.5% per year relative to 1990 levels. CO-emitting backup generation regulated by a CO tax offers a cost-effective measure to enhance robustness. It increases emissions only marginally, keeping average emissions below 1% of 1990 levels over all layouts. Our findings underscore the need for policymakers and energy stakeholders to account for interannual weather variability in future infrastructure planning.