Extreme heat and exceptionally low Danube flows are tightening electricity supply across Southeast Europe, curbing nuclear and hydro generation and increasing dependence on fossil plants and cross-border imports.
Hungary’s 2-GW Paks nuclear plant, which normally supplies as much as 40% of national electricity, was forced to halt generation in early August as low Danube levels restricted cooling.
Hungary has installed around 8 GW of solar capacity, allowing photovoltaic generation to cover as much as 80% of demand during some daytime periods. The system becomes significantly tighter after sunset, however, forcing fossil plants to increase output and pushing Hungary toward regional imports.
Romania has faced similar problems at the Cernavodă nuclear plant, while Bulgaria reduced production at Kozloduy Unit 5 by around 120 MW because of falling Danube levels. Bulgarian authorities have also moved to build a 250-300 metre structure near Kozloduy to protect water availability for the plant.
Serbia is being affected through both domestic hydrology and tighter regional supply. Danube inflows at the Djerdap hydropower complex have fallen to around 1,400 cubic metres per second, sharply restricting hydroelectric production.
Reduced nuclear availability in Hungary and Romania has at times removed an estimated 4 GW of baseload capacity from the broader regional system.
The simultaneous constraints illustrate the growing interdependence of Southeast European electricity markets. Lower generation in one country increasingly translates into stronger import demand, congested cross-border capacity and higher prices elsewhere.
The pressure is particularly visible during evening hours, when solar generation disappears but cooling demand remains elevated.
The summer of 2026 is therefore becoming a stress test not only for individual generating assets but also for the region’s ability to share limited flexible generation across increasingly interconnected markets.
