Southeast European power markets swung from nearly €200/MWh midweek to zero and negative prices during Sunday’s solar peak, while evening power still climbed above €225/MWh, exposing a widening shortage of flexibility and transmission capacity.
Serbia’s SEEPEX market captured the reversal, rising to €184.92/MWh on Sept. 3 before falling to €60.19/MWh on Sept. 6, as firmer renewable output and lower weekend demand replaced nuclear-driven scarcity with daytime oversupply.
Hungary and Romania remained much tighter, however, with prices near €197/MWh at the midweek peak and evening hours above €275/MWh, showing that surplus renewable generation was not eliminating scarcity after sunset.
The week from Aug. 31 to Sept. 6 produced one of the clearest examples yet of the region’s changing power-market structure.
Firm-generation constraints, nuclear outages and higher weekday demand tightened Central and Southeast European markets through the first half of the week. Rising renewable output and lower weekend consumption then pushed prices sharply lower.
SEEPEX day-ahead baseload rose from €132.21/MWh on Aug. 31 to €166.25/MWh on Sept. 1, €173/MWh on Sept. 2 and €184.92/MWh on Sept. 3.
Prices then fell to €149.76/MWh on Sept. 4, €114.47/MWh on Sept. 5 and €60.19/MWh on Sunday, a decline of roughly two-thirds from Thursday’s peak.
Hungary and Romania were considerably tighter during the middle of the week.
For Sept. 3 delivery, Hungary cleared at around €196.57/MWh and Romania at €196.82/MWh, while Bulgaria, Greece, Croatia and Slovenia were clustered mostly between €190 and €193/MWh.
Romania’s continued loss of nuclear generation was an important bullish factor.
With Cernavodă unavailable, the system had to rely more heavily on imports, fossil-fuel generation, hydro and renewables, increasing pressure on neighbouring Hungary and Bulgaria.
The impact was particularly visible during evening hours.
Hungarian power reached about €276.5/MWh during the Sept. 1 evening peak, while Romania climbed to around €283/MWh.
The second major feature of the week was widening geographical fragmentation.
Germany became significantly cheaper than the Central SEE markets even as west-to-east electricity flows increased.
For Sept. 3 delivery, German day-ahead baseload fell to around €133.62/MWh, leaving Hungary almost €63/MWh higher.
The divergence widened further a day later, when Germany fell to about €88.95/MWh while Hungary remained at €179.78/MWh, producing a spread of almost €91/MWh.
The persistence of that premium pointed to transmission congestion rather than an absolute shortage of electricity.
By the end of the week, rising solar production and lower weekend demand had reversed the market.
Hungary, Romania, Slovenia and Croatia all recorded negative prices during Sunday’s solar period, while Bulgaria and Greece traded around zero for several consecutive daylight hours.
Hungarian electricity fell to around -€1.5/MWh near 13:00 before rising to roughly €227.7/MWh at 20:00.
Romania followed a similar pattern, falling to around -€1/MWh before climbing back toward €228/MWh in the evening.
The move showed that solar-driven oversupply is becoming increasingly regional.
Interconnectors can absorb surplus generation when individual markets are long, but their effectiveness falls when neighbouring systems experience strong renewable output at roughly the same time.
The same synchronisation works in reverse after sunset, when several countries compete for hydro, gas, nuclear output, storage and imports.
That is increasing the value of flexible assets while weakening the economics of standalone solar.
High daily baseload prices can overstate the value actually captured by photovoltaic plants because their output is increasingly concentrated in the lowest-priced hours.
By Sunday, several markets had effectively zero-value solar periods even though evening electricity exceeded €225/MWh.
Serbia continued to trade differently from the Central SEE core.
The country briefly converged toward Hungary during the midweek tightening, but the discount widened again as renewable availability increased.
SEEPEX fell from €184.92/MWh on Thursday to €60.19/MWh on Sunday, while Hungary remained structurally firmer.
That volatility shows that the Serbia-Hungary spread is not a stable basis and can shift quickly with domestic generation, imports, cross-border schedules and network constraints.
The week therefore reinforced two increasingly important market signals.
Wide intraday spreads favour battery storage, reservoir hydro and demand response, while large geographical spreads favour interconnectors and transmission reinforcement.
Average baseload prices alone are becoming less useful for developers and traders than hourly spreads, captured prices and cross-border basis.
The week ended with Southeast Europe demonstrating both surplus and scarcity within the same market cycle: abundant renewable electricity during the day, but insufficient flexibility and transmission to deliver it where and when it carried the most value.