Why a reactor depends on a river
The Paks plant stands on the bank of the Danube and in ordinary conditions produces 40 per cent of Hungary's electricity. The drought has pulled the river down far enough that operators shut seven of the plant's eight turbines for the first time in its history. In Romania, naval engineers blew up a rock outcrop so that more water would reach the Cernavodă plant, and Slovenia and France have closed reactors because of high temperatures and low water.[1]
The link between them is thermal: a thermal or nuclear plant releases part of the heat it turns into work through water passing across the condenser. When flow falls, both the volume that can be drawn and the permitted discharge temperature start to bind. Two Copernicus Sentinel-2 images released by the European Space Agency place the same stretch about 45 km north of Budapest side by side on 9 August 2025 and 4 August 2026; in the second, sandbanks lie exposed. According to the agency's note, lows at this level have been documented since 2018.[1], [2]
Supply falls while demand climbs
Demand can climb by about 20 per cent during a heatwave, most of that rise coming from homes running air conditioning. Supply narrows at the same moment: hydropower generation in Europe fell in July to its lowest level in more than a decade, according to Ember, while 32 per cent of Italy's gas fleet is exposed to a shortage of cooling water, according to Montel, and wind speeds are low as well.[1]
The one piece of good news came from solar. Ember recorded record European Union output in June, and in Hungary solar covered as much as 80 per cent of the country's electricity during daylight. The gap, though, opens in the hours after the sun goes down while air conditioning keeps running, and without storage the daytime surplus cannot be carried into them.[1]
Where the lever actually sits
Because the gap has a time of day, the lever has a place. Two things touch the evening peak: storage and shifting demand. Both are procurement and network decisions rather than weather, which means they can be changed in the months before next summer. Adding fresh generating capacity does not reach that same hour to the same degree.[1]
If the drought runs through another summer, the number to watch is this: the battery capacity connected in the Hungarian and Romanian systems by next August, set against the turbine-hours lost to cooling limits. If storage grows while thermal constraints stay at the same level, the evening peak stops being the binding constraint. The river's level, meanwhile, will keep being read from Copernicus Sentinel-2 images alongside gauge data.[1], [2]