How Technology and Modelling Choices Shape European Wind and Solar Energy Droughts and Stress Events

In highly renewable power systems, weather-related variability increasingly translates into system stress. Dunkelflauten are multi-day to multi-week periods of unusually low wind and solar that can span multiple countries. These renewable energy droughts significantly shape storage needs, installed capacity, and transmission requirements, far more so than average conditions. Yet, simulated renewable output is highly sensitive to assumptions regarding meteorology, spatial layout, and plant‑level effects, complicating the detection of these extremes.

We address this by quantifying renewable output in a one-at-a-time sensitivity analysis varying bias-correction methods, spatial representation, technology settings, and wake-loss assumptions. Using hourly reanalysis data, we compute country‑aggregated wind and solar generation for 80 historical weather years to evaluate impacts on annual capacity factors, drought frequency and duration for wind and solar separately. These drought metrics are then linked to system outcomes by running PyPSA‑Eur for five critical weather years under a net-zero scenario, assessing changes in optimal capacities and system‑defining stress events. We find that capacity factors are driven mainly by technology specification, with bias correction exerting little influence on solar means and a moderate effect on wind, while spatial capacity layouts appear negligible for solar but more consequential for wind. Quantile‑mapping bias correction modestly improves energy drought detection, and certain technology configurations reduce risk of low‑generation. At the system level, these differences re‑order stressful periods and shift optimal capacity across technologies and regions.

By identifying the modelling choices that have the greatest impact on energy‑drought detection and associated system stress, this study helps strengthen power system resilience to weather extremes and can improve resource‑adequacy planning for a fully renewable European system