In systems with high shares of weather-dependent generation, forecast uncertainty is increasingly recognized as an important driver of balancing needs, particularly in future system configurations where conventional thermal generation is expected to be progressively displaced by VRE.

This paper evaluates the impact of sector-coupling on VRE forecast-error-driven imbalance (FEDI) in future Nordic power systems. A large-scale, long-term, multi-sector energy-system optimization model is run with lead-time-aware, spatiotemporally correlated day-ahead wind and solar forecasts across multiple weather years, so that the operational representation reflects a forecast-based day-ahead schedule rather than a perfect-foresight schedule. Nordic VRE FEDI is derived as real-time VRE availability minus the day-ahead schedule, thereby capturing how forecast uncertainty changes the VRE position between scheduling and delivery. The resulting distributions are analysed using probability density functions, standard deviations and P05/P95 quantiles.

To examine how future system structure reshapes these imbalance statistics, the analysis considers four sector-coupling scenarios: (i) a fully coupled system including electricity, heat, hydrogen and transport; (ii) electricity, heat and transport; (iii) electricity and heat; and (iv) electricity only. These alternatives lead to vastly different electricity demands and represent distinct renewable-integration pathways, resulting in different VRE portfolios and consequently, different VRE-imbalance characteristics. The analysis shows that in 2045, VRE accounts for 55–79% of installed electricity capacity across the assessed sector-coupling pathways, while the Nordic VRE FEDI standard deviation ranges from 2.49 to 8.29 GW and the P05–P95 interval expands from approximately ±4.1 to ±13.5 GW.