Southeast Europe’s power market is entering autumn with more frequent zero-price solar hours alongside persistent evening scarcity above €200/MWh. The pattern followed a summer in which drought, nuclear constraints and grid congestion widened the gap between daytime abundance and evening flexibility needs. The change was visible across the region during July and August, with the most pronounced shift occurring late in summer.
Serbia’s midday slump and evening spikes
Serbia’s SEEPEX baseload price increased from an average of €109.43/MWh in July to €136.70/MWh in August, a rise of almost 25%. The August average masked a larger hourly spread. Serbian electricity averaged about €66/MWh around midday when solar generation was strongest, then rose to €210.97/MWh at hour 19, €243.65/MWh at hour 20 and €240.25/MWh at hour 21.
The resulting evening level was nearly four times the midday value. This hourly pattern coincided with the broader regional shift toward weak daytime prices during periods of strong photovoltaic output. It also aligned with later-month moves in other central markets where negative or near-zero pricing appeared during solar peaks.
Romania’s day-ahead tightness and Danube-driven outages
Romania saw a tighter August in its day-ahead market, averaging 793.19 lei/MWh, or roughly €150/MWh, about 25% higher than July. Low Danube flows reduced hydropower production and contributed to prolonged restrictions at the Cernavodă nuclear plant. At times, those constraints removed both roughly 700 MW units and about 1.4 GW of low-marginal-cost generation from the market.
The same hydrological conditions affected Hungary’s Paks plant and Bulgaria’s Kozloduy nuclear station during parts of August. Danube water availability therefore became a variable for multiple national systems rather than a single-country factor.
Hour-by-hour scarcity alongside solar oversupply
Across Europe, installed generation capacity was sufficient and ENTSO-E identified no general continental adequacy threat. Despite that, Southeast Europe experienced scarcity during individual hours because firm capacity, hydro availability and cross-border transfer capability were not enough to fully offset the evening decline in solar output. Solar simultaneously created the opposite effect during daylight periods.
Negative prices during solar peaks in multiple markets
Greece, Bulgaria and increasingly Serbia recorded very weak midday prices during periods of strong photovoltaic production. Hungary, Romania, Croatia and Slovenia followed the same direction when weather conditions aligned across the region. By Sept. 6, Hungary, Romania, Croatia and Slovenia were posting negative prices during the solar peak, while Greece and Bulgaria cleared around zero for several consecutive intervals.
Only hours later, Hungarian and Romanian electricity returned to roughly €225-230/MWh. The shift reflected a structural change seen across summer 2026 trading patterns rather than a single-day anomaly.
Batteries expand while storage remains smaller than peak needs
Southeast Europe’s market is increasingly characterised by too much electricity in some hours and too little in others rather than only overall capacity scarcity. Daily baseload averages therefore became less representative of what individual technologies capture across different time blocks. Standalone solar was described as the most exposed case: a photovoltaic project could run when baseload averaged €150/MWh, but sell most output during hours worth €20/MWh, €10/MWh, or zero.
The impact intensifies when more solar is added unless storage, flexible consumption or export capacity expands at a similar pace. Romania reached around 1.1 GW/2.3 GWh of operating battery storage by the start of September and opened a €150 million programme targeting at least another 2.17 GWh. Developers are also moving toward longer-duration systems intended to cover several hours of the evening ramp rather than focusing only on short balancing services.
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Nuclear restrictions, reservoir hydropower and transmission bottlenecks
The summer problem extended beyond flexibility supply into weak reservoir and river conditions across parts of the region. Reservoir hydropower retained a competitive position where operators could preserve water during weak-price solar hours and dispatch after sunset to capture a flexibility premium. However, low river conditions limited that option for multiple systems during August.
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Cross-border spreads remain wide despite cheaper generation elsewhere
Transmission constraints became another major driver of price divergence within Southeast Europe. Central SEE markets traded far above Western Europe even when cheaper electricity was available in Germany. On Sept. 3, Hungary traded almost €63/MWh above Germany; on Sept. 4 the gap widened to nearly €91/MWh, even as power flows from the west increased.
The spreads indicated that additional cheap generation elsewhere does not automatically reduce SEE prices when cross-border corridors are saturated. Batteries address shifts between hours while interconnectors move power between countries, so both were described as necessary elements for managing the summer pattern.
A September baseline for volatility; October shifts with daylight decline
The outlook for September points to continued high volatility but potentially softer average conditions than the tightest August periods. Cooling demand should decline while solar generation remains strong enough to produce recurring midday oversupply, particularly during weekends. In that base case, central SEE baseload markets such as Hungary and Romania frequently trade in a broad range of €130-180/MWh, while southern and Western Balkan markets can fall materially below that level when solar and hydro conditions are favourable.
to about >€60/MWh by Sept. 6>, illustrating how quickly its basis can change with domestic supply conditions, imports, renewable forecasts and border constraints.
This made the Serbia-Hungary spread an increasingly important exposure for traders within regional price formation dynamics.
Daily shape matters more than any single forecast price level
The autumn outlook was framed around forecasting how each day’s profile develops rather than relying on one headline price level for all hours within a month. September was expected to keep cheap solar hours paired with expensive evenings, while October should have fewer zero-price intervals but potentially firmer baseload and peak values as daylight shortens.
Assets linked to both hour-to-hour shifts gain value under the pattern described for 2026 summer-to-autumn transition period
The assets gaining most value from that structure were listed as battery energy storage systems (BESS), reservoir hydropower, flexible thermal generation, demand response and cross-border transmission capacity. Summer 2026 demonstrated that Southeast Europe can experience ample electricity overall while still seeing scarcity at specific times within daily schedules.
