How significant is the “Dunkelflaute” risk in Bulgaria and Southeastern Europe?

The term Dunkelflaute (literally “dark doldrums”) describes multi-day periods of low wind and solar generation, a concern particularly in Northern and Central Europe. In Germany, such events occur 1–2 times per year and can last up to 5 days. In Bulgaria and Southeastern Europe, however, the risk is less pronounced because of the region’s more favorable renewable resource mix. Bulgaria benefits from a balanced profile: strong solar output in summer, decent wind in coastal and mountain areas, and significant hydropower (about 6–7% of annual supply, with pumped storage for flexibility).

Periods of low solar and wind do occur, but they are generally shorter and less severe than in Northern Europe. During these times, the system can rely on hydropower dispatch, imports from neighbors like Greece and Romania, and increasingly, battery storage. Modeling in the Bulgarian Resource Adequacy Assessment (BGRAA 2023) shows that covering Dunkelflaute through flexible resources is far more cost-effective than maintaining oversized coal or nuclear plants that would sit idle most of the year. Thus, while Dunkelflaute should not be ignored, in Southeastern Europe it is a manageable challenge rather than a structural barrier to high renewable shares.