Hydropower remains one of Southeast Europe’s most valuable flexibility assets, but Week 21 highlighted how uneven hydrological conditions can affect electricity pricing, cross-border flows and system-balancing needs. Regional hydro generation rose only 0.6% week-on-week to 3.95 TWh, while national outcomes diverged sharply.
Week 21 hydro output changes across Balkan markets
Croatia recorded the strongest weekly hydro rebound, with output rising by nearly 86%. Türkiye increased hydro generation by 4.8% to 2.85 TWh. In contrast, Serbia’s hydro generation fell 41.2%, Bulgaria declined 34.2%, Italy dropped 9.7%, and Greece fell 7.7% to 86.9 GWh.
The same regional aggregate therefore masked a fragmented picture across markets during Week 21. Hydro availability shifts how systems are balanced and how other resources are dispatched. When hydro output is strong, it can suppress prices, reduce thermal dispatch and ease import needs.
When hydro output weakens, systems become more dependent on coal, gas, imports or storage. In that context, Serbia’s market outcome was notable because its hydro decline did not prevent lower power prices. Even with a 41.2% hydro fall, Serbian prices dropped to €81.24/MWh, down 16.7% week-on-week.
Hydro volatility as a forecasting input for trading and financing
The Serbian price move occurred alongside factors including regional solar output, weaker demand and lower thermal costs that were sufficient to offset domestic hydro weakness during the week. However, the price decline was not presented as an ongoing protection against hydrological risk. In tighter weeks, a similar hydro shortfall could instead raise balancing costs, increase imports and widen evening price spikes.
This pattern makes hydrological volatility a key forecasting variable for traders and lenders. It also affects how market participants assess revenue stability from renewable assets and storage. Renewable developers often use annual average prices for SEE power markets, but hydrology can drive sharp weekly and seasonal deviations.
A solar project’s captured price, a wind project’s balancing exposure or a BESS project’s arbitrage value can change depending on reservoir conditions and hydro dispatch behavior . These sensitivities feed into investment assumptions where cash flows depend on short-term market dynamics rather than long-run averages.
Impacts on cross-border flows and interconnection needs
Hydro volatility also influences cross-border electricity flows. 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 . At the same time, uneven hydro distribution meant some countries strengthened export potential while others faced greater reliance on imports or thermal backup.
Croatia’s hydro rebound likely reduced pressure on imports by improving local adequacy . Serbia and Bulgaria, by contrast, had to rely more heavily on softer regional market conditions and renewable availability when their own hydro output declined . The episode illustrates how interconnections become important when transmission capacity determines whether hydrological surplus in one area can offset weakness elsewhere.
Interaction between flexible hydropower and solar generation
Hydro also interacts directly with solar as generation mixes shift across the region. As solar output grows, hydro plants can gain additional value by shifting production away from low-price midday periods into higher-value evening hours . Flexible hydropower can therefore operate in a way that resembles storage functionality within daily market cycles.
This is especially relevant for countries with reservoir-based systems that can preserve water during solar-heavy hours and dispatch during evening ramps when solar fades and prices recover . Countries with less flexible run-of-river production have fewer commercial options to adjust output in response to intraday price patterns.
The broader generation trend during Week 21 showed solar rising across SEE by 8.1%, while wind fell by 4%. With solar becoming more dominant, the role of hydro flexibility increases rather than decreases .
Policy operations and market design considerations
For policymakers, the operational role of hydro extends beyond seasonal planning. Hydro dispatch is increasingly tied to daily balancing requirements, congestion management, renewable integration and system-security strategy . This connects hydrology-driven generation changes to real-time grid constraints across multiple markets.
For investors, hydrological volatility can increase the value of hybrid portfolios that combine different revenue drivers. A portfolio combining solar, wind, BESS and contracted industrial offtake can reduce exposure to hydrological swings compared with a merchant position relying only on average market prices . Gas-fired balancing costs remain elevated with TTF close to €50/MWh, reinforcing the relative importance of flexibility from hydro during periods of weaker renewables or higher evening demand .
The Week 21 outcomes also show that Southeast Europe’s hydro position cannot be assessed only at the regional aggregate level. The regional number appeared stable while national results were sharply divergent . Those differences are expected to influence price spreads, import needs, storage economics and balancing costs as hydrology varies across countries.
Hydropower remains one of the region’s strongest assets, but its volatility is becoming one of Southeast Europe’s most important risks .
