Southeast Europe’s power system in Week 23 was shaped by a classic early-summer balancing problem: demand rose, wind weakened, solar was insufficient to cover evening needs, and system operators leaned more heavily on hydro and thermal generation. The result was a sharp shift in the regional electricity mix, with hydro providing partial relief and thermal units filling the remaining gap.
Variable renewable generation fell 8.9% week on week, dropping from 3,377 GWh to 3,075 GWh. The decline was led by wind, which fell 15.5% across the region. Solar output decreased more moderately, by 5.1%. This was a significant movement because it came at the same time as regional electricity demand increased 8.2% to 15.15 TWh.
The largest renewable declines were recorded in Romania, Croatia and Serbia, mainly because of weaker wind generation. Bulgaria and Hungary also posted lower renewable output, with weaker solar performance. Greece recorded a 6.1% decline in total renewable generation, as a 16.5% fall in wind more than offset a 1.8% increase in solar. Türkiyewas the exception, where total renewable output rose 1.2% thanks to a 61.0% jump in solar generation.
The decline in wind was especially important for the hourly price profile. Solar can depress prices during midday, but wind helps across more hours and can reduce evening marginal pressure when available. With wind weaker, residual demand became more difficult to cover during non-solar hours. That helped explain why prices retained a steep evening ramp even where midday prices were softer.
Hydro generation provided the main renewable stabiliser. Regional hydropower output increased 10.1% week on week to 3.97 TWh. Türkiye was the key driver, with hydro rising 15.4%, or 356 GWh, to 2.66 TWh. Italy, Croatia and Serbiaalso recorded hydro increases of 7.5%, 73.6% and 30.8% respectively. These gains helped moderate wholesale prices in several markets by reducing the need for more expensive thermal generation.
The hydro picture was not uniformly positive. Bulgaria, Hungary, Greece and Romania all recorded lower hydro output, reflecting weaker inflows, dispatch choices or reservoir conditions. This uneven distribution is why SEE prices diverged rather than moved together. Hydro availability can change marginal pricing sharply at the country level, especially in systems where flexible hydro competes with lignite, gas or imports.
Thermal generation rose strongly across the region. Total SEE thermal output increased 24.5% week on week to 4.22 TWh, driven by both coal/lignite and gas-fired units. The largest contribution came from Türkiye, where thermal output more than doubled to 2.03 TWh. Turkish coal generation rose 55.7%, while gas-fired production jumped 278.1%. This was the clearest example of thermal capacity stepping in to meet a sharp demand increase.
Greece also increased thermal production, with lignite output rising 66.2%, even as gas generation declined modestly. Serbia recorded higher thermal generation as well, while Romania increased thermal output by 5.2%, supported by stronger gas-fired generation. Italy was the main exception, with thermal generation down 16.7% because lower gas-fired output outweighed a rebound in coal.
The interaction between hydro and thermal determined the price outcome. Where hydro rose and demand was softer, prices had room to fall. This helps explain the Serbian price decline of 5.8%, despite the broader regional bullish demand picture. Where demand was high, hydro was insufficient or gas-linked marginal pricing remained strong, prices moved higher. Italy’s €128.09/MWh weekly average reflected that premium structure.
The renewable decline also increased the value of dispatchable flexibility. Hydro, lignite, gas and interconnector access became more important during the evening ramp. This is the core operational issue for SEE markets as summer progresses. High solar penetration can create lower midday prices, but the evening system remains exposed when wind is weak and demand is cooling-driven.
For market participants, Week 23 offered a clear balancing template. Wind weakness tightened residual load. Hydro softened the impact where water availability improved. Thermal generation set the marginal tone where demand rose sharply or hydro was insufficient. Cross-border imports filled remaining gaps. That combination is likely to remain central through the summer period, especially if heat waves lift cooling demand and gas prices remain elevated.
The regional energy transition does not remove the need for dispatchable capacity. It changes when that capacity is needed and how it is priced. Week 23 showed exactly that. Variable renewables were material but weaker; hydro was valuable but uneven; thermal generation remained essential; and prices reflected the country-by-country balance between these forces.
