Hydropower remains a key flexibility source for Southeast Europe, but Week 21 highlighted how uneven hydrological conditions can affect electricity pricing, cross-border flows and system-balancing needs. Regional hydro generation rose by 0.6% week-on-week to 3.95 TWh. Despite the small change at the regional level, national results diverged sharply.
Week 21 hydro generation changes across SEE markets
Croatia recorded the strongest weekly rebound, with hydro output increasing by nearly 86%. Türkiye raised hydro generation by 4.8% to 2.85 TWh. In contrast, Serbia’s hydro generation fell by 41.2%, while Bulgaria declined by 34.2%.
The same week also saw declines in other markets: Italy’s hydro output dropped by 9.7%, and Greece fell by 7.7% to 86.9 GWh. The spread of weekly outcomes across countries contributed to different local system conditions.
Hydro’s role in balancing and price formation
In Southeast Europe, hydro is described as the region’s main natural balancing instrument. When hydro output is strong, it can suppress prices, reduce thermal dispatch and ease import needs. When hydro weakens, systems can become more dependent on coal, gas, imports or storage.
Serbia’s position was highlighted by both generation and price movements. Even with a 41.2% hydro decline, Serbian prices fell to €81.24/MWh, down 16.7% week-on-week.
Implications for forecasting and market operations
The Serbian price drop occurred alongside factors including regional solar output, weaker demand and lower thermal costs, which were sufficient to offset domestic hydro weakness during Week 21. The same hydrological shortfall could have led to different outcomes in tighter weeks, including higher balancing costs, stronger imports and wider evening price spikes.
This pattern increases the importance of hydrology as a forecasting variable for traders and lenders. It also affects how developers assess revenue streams when market models rely on annual average prices rather than weekly and seasonal deviations.
Cross-border flows and interconnection constraints
Hydro volatility also influences cross-border electricity flows. During Week 21, regional net electricity imports decreased by 34.6% to 1.03 TWh, partly linked to improved renewable and hydro availability in several markets.
The uneven distribution of hydro output meant some countries strengthened export potential while others faced greater exposure to imports or thermal backup. Croatia’s rebound was associated with reduced pressure on imports, while Serbia and Bulgaria relied more heavily on softer regional conditions and renewable availability.
The developments also point to the role of transmission capacity in determining whether hydrological surplus in one market can offset weakness elsewhere. Where interconnections are constrained, surplus may not translate into support for neighboring systems.
Interaction between hydropower flexibility and solar growth
Hydro interacts directly with solar as additional solar capacity changes daily generation patterns. As solar grows, hydro plants can shift output away from low-price midday periods into higher-value evening hours.
This is particularly relevant for reservoir-based hydropower systems that can preserve water during solar-heavy hours and dispatch during evening ramps when solar fades and prices recover. For run-of-river systems with less flexibility, commercial options tied to shifting generation are more limited.
Renewables mix shifts and dispatch planning needs
The broader renewables trend in the same week showed solar rising across Southeast Europe while wind fell. Solar output increased by 8.1% in Week 21, while wind declined by 4%.
As solar becomes more dominant, flexible hydro is positioned as more valuable for balancing needs rather than less so. For policymakers, this raises operational questions because hydro dispatch extends beyond seasonal planning into daily balancing, congestion management, renewable integration and system-security strategy.
Investment considerations amid gas price levels
The investment implications include changes in how portfolios manage exposure to hydrological swings. Hydro volatility can increase the value of hybrid portfolios combining solar, wind, BESS and contracted industrial offtake compared with merchant assets relying only on average market prices.
Gas-fired balancing costs also remain a factor in the region’s flexibility economics. With TTF close to €50/MWh, gas-fired balancing is described as costly, which increases the relative value of hydro flexibility during periods when renewable output is weak or evening demand rises.
Narrowing from regional averages to national outcomes
The Week 21 results indicate that Southeast Europe’s hydro position cannot be assessed solely using regional aggregates. While the regional number appeared stable after a small week-on-week increase in total generation, national outcomes were markedly different across countries.
This divergence is expected to influence price spreads, import requirements, storage economics and balancing costs as hydrological conditions vary from one market to another within the region.