Extreme heat and exceptionally low Danube flows are tightening electricity supply across Southeast Europe. The constraints are curbing nuclear and hydro generation while increasing reliance on fossil plants and cross-border imports.
Hungary’s Paks outage and solar-driven daytime coverage
Hungary’s Paks nuclear plant, with a capacity of 2 GW, was forced to halt generation in early August. Low Danube levels restricted cooling, ending output from the plant. Paks normally supplies as much as 40% of national electricity.
Hungary has installed around 8 GW of solar capacity. Photovoltaic generation can cover as much as 80% of demand during some daytime periods. After sunset, the system becomes significantly tighter, requiring fossil plants to increase output and increasing pressure for regional imports.
Nuclear and hydro constraints in Romania and Bulgaria
Romania has faced similar problems at the Cernavodă nuclear plant. Bulgaria reduced production at Kozloduy Unit 5 by around 120 MW due to falling Danube levels. Bulgarian authorities have also moved to build a 250-300 metre structure near Kozloduy to protect water availability for the plant.
The combined nuclear constraints in Hungary and Romania have at times removed an estimated 4 GW of baseload capacity from the broader regional system. This reduction affects supply balance alongside lower hydro availability linked to river conditions.
Serbia’s hydrology impacts and evening pressure on supply
Serbia is 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. The lower inflows sharply restrict hydroelectric production.
The simultaneous constraints highlight growing interdependence across Southeast European electricity markets. Lower generation in one country can translate 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 becoming a stress test for individual generating assets and for the region’s ability to share limited flexible generation across increasingly interconnected markets.
