Solar hits 84.44 TWh as hydro hits seven-summer low in ten systems

At 13:00, reservoir hydro output across Austria, Germany, Spain, Portugal, France and Italy averaged 247 MW this summer, down from 1,050 MW in 2020. At 21:00, it was almost unchanged: 1,483 MW in 2026 versus 1,500 MW in 2020. The daytime withdrawal is the clearest sign that Europe’s water-and-sun system is being operated differently, as solar generation reached 84.44 TWh while hydro fell to 31.65 TWh between June 1 and August 15.

The water shortage was real, but uneven. Reservoir stock across the ten systems stood at 88,499 GWh in week 31, 7.7% below the 2015–2025 median and the third-lowest reading in twelve years. France’s storage closed the period 23.4% below its median, while the Alpine group was 12.7% below and the Danube and South East Europe group 7.8% below. Iberia moved in the opposite direction: Spanish and Portuguese storage stood 96% and 137% above their levels during that summer in 2022.

Solar filled the continental accounting gap, but not necessarily the local one. Against the 2020–2025 average, hydro generation was 12.61 TWh lower in 2026, while solar was 34.74 TWh higher. Combined hydro and solar output reached 116.09 TWh, its highest level in the seven-year record and 47.0% above the 2022 drought summer. The increase was not caused by low rivers: solar capacity had been installed on a multi-year schedule, independently of this summer’s hydrology.

The operating change is visible in the hours of the day. Across the six systems, reservoir hydro’s share delivered between 10:00 and 16:00 fell from 25.6% in 2020 to 10.1% in 2026, while its evening share between 18:00 and 23:00 rose from 28.9% to 35.3%. Water can therefore be held back during the solar-heavy middle of the day and used more in the evening, when the solar contribution is lower. The continental balance still depends on interconnections and on whether surplus solar appears where and when the deficit occurs.

So what changes in practice? A dry summer no longer maps as directly onto a lower combined hydro-and-solar total: in this panel, solar covered the hydro shortfall nearly three times over. But the benefit is a system effect, not a guarantee for every region. Spain and Germany accounted for 54% of the solar increment, while the largest water losses occurred elsewhere. The immediate gain is flexibility—reservoirs shifting output toward evening—provided the grid can move power across the continent.