Hydropower remains a key flexibility source in 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, while national outcomes diverged sharply.
Croatia recorded the strongest weekly rebound, with hydro output up by nearly 86%. Türkiye increased hydro generation by 4.8% to 2.85 TWh, while Serbia saw hydro output fall by 41.2%. Bulgaria declined by 34.2%, Italy dropped by 9.7%, and Greece fell by 7.7% to 86.9 GWh.
Hydrology’s impact on balancing, dispatch and imports
The regional pattern matters for market operations because hydro is used as a balancing instrument in Southeast Europe. When hydro output is strong, it can suppress prices, reduce thermal dispatch and ease import requirements. When hydro weakens, systems can become more reliant on coal, gas, imports or storage.
Serbia’s market position was notable during Week 21 despite the 41.2% hydro decline. Serbian prices still fell to €81.24/MWh, down 16.7% week-on-week. The move coincided with factors including regional solar availability, weaker demand and lower thermal costs.
The same hydrological shortfall could have produced different outcomes in tighter conditions, including higher balancing costs, stronger imports and wider evening price spikes. This makes hydro volatility a variable that traders and lenders need to incorporate into forecasting.
Renewables variability and cross-border flow adjustments
Hydrology also affects how developers model revenue from renewable assets in SEE power markets. Projects are often assessed using annual average prices, but weekly and seasonal deviations tied to reservoir conditions can change captured prices and balancing exposure. The value of solar, wind and BESS outcomes can therefore shift depending on hydro dispatch behavior.
Cross-border flows were also influenced during Week 21 as net electricity imports fell by 34.6% to 1.03 TWh. The decline was linked in part to improved renewable and hydro availability across several markets. However, the uneven distribution of hydro output meant some countries strengthened export potential while others relied more on imports or thermal backup.
Croatia’s hydro rebound likely reduced pressure on imports, while Serbia and Bulgaria had to depend more on broader regional market softness and renewable availability. The role of interconnections becomes more prominent because hydrological surplus in one market can offset weakness elsewhere only where transmission capacity allows transfers.
Solar growth increases the value of flexible hydro
Hydro output interacts directly with solar generation as solar expands across the region. With more solar on the system, hydro plants can shift production away from low-price midday periods toward higher-value evening hours. Flexible hydro therefore functions as a form of operational flexibility alongside other storage-like resources.
This is particularly relevant for countries with reservoir-based hydropower systems that can preserve water during solar-heavy periods and dispatch during evening ramps when solar fades and prices recover. Where production is less flexible due to run-of-river constraints, commercial options tied to shifting output are more limited.
The broader generation mix moved further in this direction during Week 21, with solar output up by 8.1% across SEE while wind fell by 4%. As solar becomes more dominant, the flexibility contribution from hydro becomes more important for balancing needs.
Policy operations and investment implications amid gas cost sensitivity
For policymakers, the changing role of hydropower affects operational planning beyond seasonal generation schedules. Hydro dispatch increasingly links to daily balancing requirements, congestion management, renewable integration and system-security considerations.
For investors, hydro volatility can increase the rationale for hybrid portfolios that combine multiple revenue streams such as solar, wind, BESS and contracted industrial offtake. A merchant approach relying only on average market prices faces greater uncertainty when hydrology shifts week-to-week.
TFF-linked gas costs also reinforce the importance of flexibility because gas-fired balancing remains costly when TTF is close to €50/MWh. In such conditions, hydro flexibility can be especially relevant during periods when renewable output is weak or evening demand rises.
The Week 21 outcomes also show that Southeast Europe’s hydrological position cannot be assessed solely using regional aggregates. While the regional figure appeared stable, national results differed markedly, affecting price spreads, import needs, storage economics and balancing costs.
[No additional facts provided beyond these points.]
