ACER’s 2026 assessment says the electricity price gap between Southeast European and Central European markets persisted throughout 2025 and into early 2026. The regulator links the pattern to structural weaknesses in flexibility, network utilisation and regional market integration. The assessment argues the crisis cannot be explained simply by temporary fuel costs or extreme weather events.
2024 summer conditions and post-sunset solar shortfalls
ACER reviewed extreme summer conditions in 2024, when average peak electricity prices in affected Southeast European markets reached around €350/MWh. The main pressure occurred after sunset as solar generation declined rapidly while electricity demand stayed elevated. ACER says the region lacked sufficient flexible resources to replace the lost solar output. Limited import capacity, including restrictions associated with planned network maintenance, prevented cheaper Central European electricity from fully covering the shortage.
Transmission availability, congestion and cross-zonal trade
ACER estimates that 147 of the most severe price spikes could have been avoided if an EU requirement to make at least 70% of relevant transmission capacity available for cross-zonal trade had been met. ACER notes this does not require every transmission line to run continuously at 70% of physical thermal capacity, because regulatory methodology includes reliability margins and contingencies. The regulator says the estimate points to domestic congestion and insufficiently coordinated operational decisions that can leave too little transmission capacity available to the integrated electricity market.
Markets affected and the Central Europe comparison corridor
The affected Southeast European markets identified by ACER are Slovenia, Croatia, Hungary, Romania, Bulgaria and Greece. For comparison, ACER cites Austria and Slovakia as Central European reference markets. ACER says electricity flows across the corridor are shaped by outages and network constraints that can arise far from national borders where transmission capacity is allocated. It adds that bilateral capacity figures cannot fully represent behaviour in a highly interconnected and meshed network.
Flow-based coupling, outage planning and grid-enhancing tools
ACER calls for full implementation of flow-based market coupling and stronger regional coordination. The regulator also requests improved outage planning, greater use of curative remedial actions and faster delivery of high-impact network investments. ACER supports wider deployment of grid-enhancing technologies, including dynamic line rating. It says dynamic line rating can increase available transmission capacity by more than 50% on certain constrained network elements under favourable conditions.
Evening supply needs beyond additional interconnection
ACER says stronger interconnection alone will not address the region’s evening supply problem. If several Southeast European countries experience the same post-sunset decline in solar generation, neighbouring markets may all attempt imports simultaneously. The regulator lists storage, demand response, flexible hydropower and fast-start generation as essential components for resilience. It also says cross-border trading can reduce scarcity costs by pooling available resources but cannot create surplus electricity when the entire region faces a simultaneous shortage.
Impacts on market value for flexibility and generation assets
ACER describes commercial implications from persistent price separation across markets. The pattern creates opportunities for battery storage and electricity traders while increasing costs for energy-intensive industrial consumers. It also weakens expectations that renewable expansion will automatically translate into cheaper electricity. ACER adds that it changes relative value between generation and flexibility assets, noting that a megawatt of flexible capacity near a congested border or within a constrained market can be more valuable than an equivalent megawatt in an unconstrained area.
Policy focus on operational coordination and integrated market rules
ACER says its findings shift debate away from simply building more transmission lines. The regulator argues Southeast Europe needs to use existing infrastructure more efficiently, coordinate network outages more effectively and apply common market rules consistently. It states operational reforms and additional flexibility could reduce price volatility while larger interconnectors and grid investments are developed.
The regulator frames the issue as increasingly a market-design and flexibility challenge as well as a generation challenge. ACER says closing the gap requires treating Southeast Europe’s electricity system as an integrated regional market rather than separate national grids.
