Electricity production from Slovenia’s major river-based hydropower plants fell sharply in 2025, reflecting less favorable hydrological conditions compared to 2024. Plants on the Drava, Sava, and Soca rivers delivered just over 3.8 TWh to the transmission network, a decline of almost 25% from the previous year, which had been exceptionally strong. Despite the drop, actual output remained close to official projections, lagging the national electricity balance forecast by only 2.4%.
Data from the national environmental agency show that river flows across Slovenia were below average throughout the year. Total water volumes in 2025 were over 5% below the long-term average for the 1991–2020 reference period, with conditions gradually worsening from the southwest toward the northeast. The Mura and Drava rivers recorded their third-lowest average annual flows since 1981.
Hydrological conditions were most favorable early in the year. March was the wettest month, while January also saw above-average water levels. From June onward, river flows consistently remained below average, though Slovenia did not experience prolonged or extreme droughts. These patterns directly impacted hydropower production, with the largest year-on-year drop recorded on the Drava, where HPPs supplied 2,162.5 GWh, roughly one-third less than in 2024. Output from plants on the upper and lower Sava also declined by about 15%, totaling 875 GWh.
By contrast, Soca river plants benefited from comparatively favorable conditions, producing 793 GWh, up 2.7% from 2024 and exceeding initial production forecasts by about one-third.
Across all domestic generation sources, Slovenia supplied 11,786.4 GWh to the transmission network in 2025, a 14.7% decrease compared to the previous year. This decline was heavily influenced by the Sostanj thermal power plant, where output fell more than 39%, dropping from 3,021.4 GWh in 2024 to 1,836.2 GWh.
Part of the shortfall at TPP Sostanj was offset by increased generation at the TE-TOL plant, where a new gas-fired unit nearly tripled output, rising from 186.7 GWh to 549.2 GWh year-on-year.