Southeast European power markets swung from near €200/MWh midweek to zero and negative prices during Sunday’s solar peak, while evening electricity still climbed above €225/MWh, highlighting a widening shortage of flexibility and transmission capacity.
Serbia’s SEEPEX market captured the sharp reversal, rising to €184.92/MWh on Sept. 3 before falling to €60.19/MWh on Sept. 6. Stronger renewable generation and weaker weekend demand replaced the nuclear-driven scarcity seen earlier in the week with pronounced daytime oversupply.
Hungary and Romania remained considerably tighter, however. Prices approached €197/MWh at the midweek peak, while evening prices exceeded €275/MWh, demonstrating that abundant renewable generation during daylight hours was not sufficient to eliminate scarcity after sunset.
The Aug. 31-Sept. 6 period provided one of the clearest demonstrations yet of the changing structure of Southeast Europe’s electricity market.
Constraints on firm generation, nuclear outages and stronger weekday demand tightened Central and Southeast European markets during the first half of the week. The subsequent increase in renewable output, combined with weaker weekend consumption, then triggered a sharp price reversal.
SEEPEX day-ahead baseload prices climbed 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.
The market subsequently eased to €149.76/MWh on Sept. 4, €114.47/MWh on Sept. 5 and €60.19/MWh on Sunday, leaving prices roughly two-thirds below Thursday’s peak.
Nuclear outages keep Central SEE markets tight
Hungary and Romania were substantially tighter during the middle of the week.
For Sept. 3 delivery, Hungary cleared at around €196.57/MWh, while Romania reached €196.82/MWh. Bulgaria, Greece, Croatia and Slovenia traded mostly within the €190-193/MWh range.
Romania’s continued loss of nuclear generation remained an important bullish factor. With Cernavodă unavailable, Romania had to rely more heavily on imports, fossil-fuel generation, hydro and renewables, increasing pressure on neighbouring markets, particularly Hungary and Bulgaria.
The impact was most pronounced during the evening peak.
Hungarian electricity reached approximately €276.5/MWh during the Sept. 1 evening peak, while Romania climbed to around €283/MWh.
Transmission constraints widen regional price gaps
A second defining feature of the week was increasing geographical fragmentation.
Germany became significantly cheaper than 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 the following day. Germany dropped to approximately €88.95/MWh, while Hungary remained at €179.78/MWh, creating a spread of almost €91/MWh.
The persistence of such a large premium pointed more toward transmission congestion than an outright shortage of electricity.
Solar oversupply reverses the market
By the end of the week, stronger solar generation and weaker weekend demand had completely reversed the market dynamic.
Hungary, Romania, Slovenia and Croatia all recorded negative prices during Sunday’s solar peak, while Bulgaria and Greece traded around zero for several consecutive daylight hours.
Hungarian electricity fell to approximately -€1.5/MWh around 13:00 before rebounding to roughly €227.7/MWh at 20:00.
Romania followed a similar pattern, falling to around -€1/MWh before recovering to approximately €228/MWh during the evening.
The simultaneous price movements show that solar-driven oversupply is becoming an increasingly regional phenomenon.
Interconnectors can redistribute surplus generation when individual markets are long, but their ability to absorb excess electricity is constrained when neighbouring systems experience strong renewable output at roughly the same time.
The same synchronisation operates in reverse after sunset, when multiple countries simultaneously compete for hydro, gas, nuclear generation, storage and imports.
This dynamic is increasing the value of flexible assets while placing additional pressure on the economics of standalone solar projects.
High daily baseload prices can increasingly overstate the value captured by photovoltaic generation because solar output is concentrated in the lowest-priced hours.
By Sunday, several regional markets had effectively zero-value solar periods even as evening electricity prices exceeded €225/MWh.
Serbia remains an important outlier
Serbia continued to trade differently from the Central SEE core.
SEEPEX briefly converged toward Hungarian price levels 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.
The sharp movement demonstrates that the Serbia-Hungary price spread is not a stable differential and can change rapidly depending on domestic generation, imports, cross-border schedules and network constraints.
Flexibility becomes the key market signal
The week reinforced two increasingly important investment signals.
Wide intraday spreads strengthen the economics of battery storage, reservoir hydropower and demand response, while persistent geographical spreads increase the value of interconnectors and transmission reinforcement.
For developers and traders, average baseload prices are therefore becoming less informative 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 capacity to deliver that energy where and when it carries the greatest value.
