Hydropower remains one of Southeast Europe’s key flexibility resources, but Week 21 highlighted how uneven hydrological conditions can affect electricity pricing, cross-border movements and system-balancing requirements. Regional hydro generation rose by 0.6% week-on-week to 3.95 TWh, while national outcomes diverged sharply across markets. The same week also coincided with changes in net electricity imports.
In Week 21, Croatia recorded the strongest weekly hydro rebound, with output increasing by nearly 86%. Türkiye raised hydro generation by 4.8% to 2.85 TWh. By contrast, Serbia saw hydro generation fall by 41.2%, Bulgaria declined by 34.2%, Italy dropped by 9.7%, and Greece fell by 7.7% to 86.9 GWh.
Hydrological variation and its impact on balancing needs
The regional divergence matters because hydro is a primary natural balancing instrument in Southeast Europe. When hydro output is stronger, it can suppress prices, reduce thermal dispatch and ease import needs. When hydro weakens, systems can become more reliant on coal, gas, imports or storage.
Serbia’s market position was notable in Week 21. Even after a 41.2% decline in hydro generation, Serbian prices fell to €81.24/MWh, down 16.7% week-on-week. The price drop occurred alongside regional solar availability, weaker demand and lower thermal costs.
The same magnitude of hydro shortfall could have produced different outcomes in tighter conditions, including higher balancing costs, stronger imports and wider evening price spikes. This makes hydrological volatility a key variable for forecasting used by traders and lenders.
Cross-border flows shift as hydro availability changes
During Week 21, regional net electricity imports fell 34.6% to 1.03 TWh, partly linked to improved renewable and hydro availability in several markets. However, the distribution of hydro output was uneven across countries.
The differing hydro profiles meant some markets strengthened their export potential while others faced greater exposure to imports or thermal backup. Croatia’s rebound likely reduced pressure on imports and supported local adequacy, while Serbia and Bulgaria relied more heavily on broader regional market softness and renewable availability.
The role of interconnections also came into focus because hydrological surplus in one market can offset weakness elsewhere only where transmission capacity allows power to move between systems.
Hydro flexibility alongside solar growth
Hydro interacts directly with solar as solar output expands across Southeast Europe. As solar generation grows, hydro plants can shift production away from low-price midday periods toward higher-value evening hours.
This is particularly relevant for countries with reservoir-based hydro systems that can preserve water during solar-heavy hours and dispatch during evening ramps when solar fades and prices recover. In contrast, countries with less flexible run-of-river production have fewer commercial options.
Solar output across SEE increased 8.1% in Week 21 while wind fell 4%. With solar becoming more dominant, the value of hydro flexibility increases rather than decreases.
Policy operations and investment exposure to hydrology
For policymakers, the changing pattern affects how hydro dispatch is handled operationally beyond seasonal planning. Hydro dispatch increasingly feeds into daily balancing, congestion management, renewable integration and system-security strategy.
For investors, hydro volatility affects portfolio design across solar, wind and storage. A hybrid portfolio combining solar, wind, BESS and contracted industrial offtake can reduce exposure to hydrological swings compared with a merchant asset relying only on average market prices.
Gas-fired balancing remains costly with TTF close to €50/MWh. That cost level reinforces the relative value of hydro flexibility during periods when renewable output is weak or evening demand rises.
The Week 21 pattern also indicated that Southeast Europe’s hydro position cannot be evaluated only using the regional aggregate figure because national outcomes were sharply divergent. Those differences are expected to influence price spreads, import needs, storage economics and balancing costs.
Hydropower remains one of the region’s strongest assets but its volatility is among its most important risks.
