Southeast European electricity prices are expected to stay fragmented through September and October as transmission constraints limit the ability of cheaper Central European power to reach Hungary, Romania and the Balkans during tight hours. Summer trading showed that adding generation does not automatically lead to price convergence across the region. Cross-border flows can increase without eliminating regional price differences.
Hungary-Germany spread and separate zones during summer trading
On Sept. 4, Hungary traded almost €91/MWh above Germany even as west-to-east imports rose. Serbia, Bulgaria and Greece frequently operated as separate price zones, with outcomes tied to renewable availability and border capacity. The pattern indicates that regional market coupling is constrained during specific hours.
ACER points to cross-zonal capacity and evening flexibility
The ACER assessment cites insufficient cross-zonal capacity and evening flexibility as structural causes behind earlier SEE price spikes. ACER urged grid operators to apply an EU requirement to make at least 70% of transmission capacity available for cross-border trade. The regulator said these factors affect how electricity can be moved between bidding zones when demand peaks in the evening.
The issue is expected to become more visible in autumn. September is forecast to continue delivering strong solar output and occasional regional surpluses, while October brings shorter daylight hours and an earlier evening ramp. These seasonal shifts change the timing of supply availability relative to peak demand periods.
Autumn optimisation roles across Hungary, Romania, Bulgaria, Croatia and Slovenia
Hungary is likely to remain the main regional optimisation hub, taking in electricity from Austria, Slovakia and Romania before redistributing supply toward Serbia, Croatia and Slovenia. Romania’s position will depend heavily on nuclear and hydro availability. Bulgaria’s export potential is expected to be stronger when Kozloduy operates normally.
Croatia and Slovenia are described as structurally more dependent on imports during periods of weak hydro. Serbia’s market role can switch between importer and exporter within days, contributing to volatility in the SEEPEX-HUPX spread. The risk highlighted for autumn focuses on operational constraints rather than overall generation levels.
Main autumn risk: limited ability to move lower-priced power into SEE
The main autumn trading risk is not a lack of electricity across Europe. Instead, it is insufficient capacity to move lower-priced electricity into SEE during the hours when the region needs it most. This constraint aligns with the broader expectation of persistent price fragmentation through September and October.
