Short-term renewable energy forecast errors in Europe: Spatial dependence and smoothing potential

Renewable energy forecast errors result in costly countermeasures, including countertrading, redispatch, and increased operating reserves. Correlated regional forecast errors increase risks in renewable energy portfolios, yet their spatial dependencies are poorly understood. Therefore, we derive site-specific correlation lengths and assess the potential for spatial smoothing of forecast errors across Europe for intraday up to two-days-ahead lead time. By increasing site separation beyond 150 km, weather-driven renewable energy forecast errors effectively become uncorrelated, reducing mean absolute errors and extreme forecast error events by over 33% for wind energy and approximately 25% for solar energy at day-ahead lead times. Additionally, accounting for principal error directions can reduce the necessary site separation for effective error mitigation. Finally, we evaluate current and planned renewable energy sites in Europe based on these findings and identify regions with elevated forecast errors. This study provides a characterization of renewable energy forecast errors in Europe and offers actionable insights for decision-makers designing resilient renewable energy portfolios.