Slovenia’s power system is increasingly influenced by a weak hydrological year, with declining water availability reducing hydropower output in the opening months of 2026. Lower generation has contributed to a greater reliance on gas-fired electricity to cover domestic demand.
April hydropower deliveries fall below last year
The decline was most visible in April, when hydropower plants delivered 191.5 GWh of electricity to the transmission network. That figure was more than 49% lower than in the same month of the previous year. Reduced river flows across the country were reflected in the April performance.
The weakness extended beyond a single month, with hydropower facilities on the Drava, Sava, and Soča generating a combined 909.5 GWh over the first four months of 2026. This was 401.6 GWh less than during the same period in 2025, representing a decline of more than 30%. Output also fell below levels projected in national generation plans.
Domestic generation down as coal cannot fully offset hydro shortfall
The hydropower shortfall affected Slovenia’s overall electricity output between January and April. Domestic generation totaled 4,055.8 GWh, down 9.2% year-on-year. Coal-fired production did not fully compensate for reduced hydro output during the period.
The limits were linked to TPP Šoštanj’s role in ensuring district heating supply for the Šaleška Valley. Operating constraints reduced flexibility for electricity generation alongside heat obligations. As a result, thermal generation from gas increased its share of the mix.
Gas plants expand output as TE-TOL and TPP Brestanica rise
Natural gas plants took on a larger role in meeting demand as hydropower output remained weak. The largest increase came from Ljubljana’s TE-TOL facility, where a new gas-fired unit raised production significantly. In the first four months of 2026, TE-TOL generated 370.4 GWh, more than doubling compared with the same period in 2025.
Additional support came from TPP Brestanica, where electricity production rose by nearly 60% year-on-year to 15.4 GWh. Together, these changes show how additional flexible thermal capacity is being used to support system requirements under low hydro conditions.
Early-year hydro weakness points to below-average conditions
The figures indicate that 2026 could become one of Slovenia’s weakest hydrological years in recent history. Early-year hydropower performance is treated as an indicator for annual output trends based on current patterns described in the data.
With hydro generation running below projections and domestic supply relying more heavily on thermal sources, alternative generation continues to be used to maintain balance in Slovenia’s electricity system through the early part of the year.
