Slovenia’s electricity system is increasingly being shaped by a weak hydrological year, as declining water availability significantly reduced hydropower output in the opening months of 2026 and forced a greater reliance on gas-fired generation to meet domestic demand.
The decline was particularly pronounced in April, when hydropower plants delivered just 191.5 GWh of electricity to the transmission network. This represented a drop of more than 49% year-on-year, underscoring the severity of reduced river flows across the country.
The weakness was not limited to a single month. Hydropower facilities on the Drava, Sava, and Soča rivers generated a combined 909.5 GWh during the first four months of the year, which is 401.6 GWh less than in the same period of 2025, a decline of more than 30%. Production also fell significantly below levels projected in national generation plans.
This shortfall had a clear impact on Slovenia’s overall electricity output. Between January and April, domestic generation totaled 4,055.8 GWh, marking a year-on-year decrease of 9.2%. At the same time, coal-fired generation was unable to fully compensate for reduced hydro production, as TPP Šoštanj operated under constraints related to its role in ensuring district heating supply for the Šaleška Valley, limiting its flexibility in electricity generation.
As a result, natural gas plants played a significantly larger role in the generation mix. The strongest increase came from Ljubljana’s TE-TOL facility, where a new gas-fired unit substantially boosted output. During the first four months of 2026, the plant produced 370.4 GWh, more than doubling its generation compared to the same period in 2025.
Additional support came from TPP Brestanica, which also recorded strong growth, with electricity production rising by nearly 60% year-on-year to 15.4 GWh. These developments highlight the growing importance of flexible thermal capacity in maintaining system stability.
Overall, the data reinforce concerns that 2026 could become one of the weakest hydrological years in recent history for Slovenia. Given that early-year hydropower performance is often a key indicator of annual output, current trends suggest continued below-average generation, increasing reliance on alternative sources to ensure electricity system balance.
