Hydro generation across ten systems with complete records reached 31.65 TWh between June 1 and August 15, 2026, the weakest of seven summers and 6.0% below the 33.69 TWh recorded over the same calendar window in the drought summer of 2022, according to pv magazine.
The shortfall was concentrated in reservoir plants. Measured against each system's own 2020 to 2025 average, reservoir output over the same period fell 42.7% in Austria, 37.9% in Italy, 29.1% in Romania and 25.9% in France, pv magazine reported.
Solar filled the gap. Across fifteen systems in the sample, summer solar generation climbed from 34.1 TWh in 2020 to 88.7 TWh in 2026, per pv magazine.
The growth in daytime photovoltaic supply also rewrote pumped-storage operating patterns. The peak charging hour moved from around 04:00 to between 13:00 and 14:00, and the correlation between hourly solar output and hourly pumping rose from zero to 0.86 over six summers, according to pv magazine. Pumps that once drew cheap overnight power now run on midday surplus.
That re-timing matters because reservoir hydro and pumped storage are the flexible resources systems lean on when thermal margins tighten in summer. With reservoir output down by more than a quarter in four of the countries measured, the stored-energy buffer available for evening peaks is smaller than in any of the prior six summers in the dataset.
The solar figure is the counterweight: 88.7 TWh in 2026 is more than two and a half times the 34.1 TWh delivered across the same fifteen systems in 2020, pv magazine reported. The pumping correlation of 0.86 indicates how tightly the charging cycle now tracks that midday output.