The next major energy constraint in Southeastern Europe will not be generation. It will be transmission.
The first half of May 2026 showed a regional power system already moving toward congestion-led market behavior. Prices increased sharply even though demand fell. Solar output rose, but it did not prevent higher system prices. Cross-border flows shifted materially, while several corridors showed signs of tightening, reversal or structural imbalance. The data points to a market where electricity value is increasingly determined not only by how much power is produced, but by whether it can physically reach the right market at the right hour.
This is the beginning of a congestion decade.
The regional figures are already telling. Net exports across the broader HU+SEE system deteriorated from -767 MW to -1,170 MW, meaning the region became more import-dependent during the observed period. Flows toward Italy reversed from +310 MW to -148 MW, while the Bulgaria–North Macedonia–Albania flow position toward Greece worsened to -1,129 MW.
That movement is commercially important because the Balkans have historically relied on cross-border flexibility to smooth national generation imbalances. Hydro-rich systems exported during favorable hydrology. Coal-heavy systems provided baseload. Greece, Italy, Hungary and Romania acted as price anchors depending on season, weather and fuel spreads.
That structure is becoming less predictable.
The region is now dealing with several simultaneous pressures. Solar capacity is growing faster than grid reinforcement. Coal plants are becoming less reliable. Nuclear outages have stronger price impact. Hydro output is less consistently monetizable. Gas is returning as the marginal balancing fuel. CBAM is altering buyer behavior for Western Balkan electricity. At the same time, cross-border capacity remains limited by old network design, slow permitting and fragmented national investment planning.
The result is a market in which congestion becomes both a risk and a revenue source.
For traders, congestion creates spreads. For developers, it creates curtailment risk. For banks, it creates uncertainty around captured prices. For TSOs, it creates operational stress. For governments, it creates political pressure as renewable projects wait for grid access while consumers face higher wholesale volatility.
This is already visible in the regional price map. Romania’s OPCOM averaged €115.88/MWh in the first half of May, trading at a €7.65/MWh premium to Hungary’s HUPX. Bulgaria’s IBEX averaged €104.98/MWh, Croatia’s CROPEX €105.77/MWh, Slovenia’s BSP €103.85/MWh, Serbia’s SEEPEX €101.61/MWh, Montenegro’s BELEN €98.76/MWh, and Albania’s ALPEX €98.60/MWh.
These differences are not large enough to indicate a fully fractured market, but they are wide enough to show that national and corridor constraints are increasingly shaping value.
Romania is a key example. It combines major generation resources, large renewable potential, nuclear exposure, hydro flexibility and cross-border links toward Hungary, Bulgaria, Serbia, Moldova and Ukraine. Yet it also faces network connection disputes and regulatory pressure around new grid access rules. The May data showed Romania at the top of the SEE price stack, above Hungary, Bulgaria and Serbia. That premium reflects not only generation conditions but also the difficulty of translating regional supply into smooth price convergence.
Bulgaria offers another version of the same problem. The country is rapidly becoming a solar and battery storage hub, but storage growth itself is a response to grid pressure. A system with too much uncontrolled solar and insufficient transmission capacity begins to experience curtailment, negative-price risk and local congestion. Batteries reduce the problem, but they do not replace the need for stronger transmission corridors.
Greece is the clearest warning sign. Strong solar growth, increasingly visible curtailment pressure and low-price uncertainty for small investors show what happens when renewable deployment outruns system flexibility. The May flow data, where northern flows toward Greece deteriorated sharply, points to a market still heavily dependent on imported balancing under certain conditions, even as domestic solar can depress prices during other hours.
That contradiction will become more common across SEE.
Countries may simultaneously experience renewable oversupply in one zone and scarcity in another. A solar-heavy region can produce negative prices at noon while the national system still needs expensive imports in the evening. This is not a failure of renewable generation. It is a failure of grid timing, flexibility and spatial coordination.
Serbia sits directly inside this emerging congestion map.
Its geographic position gives it strategic importance between Hungary, Romania, Bulgaria, Bosnia and Herzegovina, Montenegro, Kosovo and North Macedonia. It can become a regional balancing corridor, but only if transmission investment, market coupling, grid-code enforcement and renewable connection planning keep pace with project development.
If not, Serbia risks becoming a congestion buffer between stronger surrounding markets rather than a value-capturing hub.
The same logic applies to Montenegro. Its hydropower and wind resources have strong regional value, but export monetization increasingly depends on access to premium corridors. EPCG’s reported €13 million Q1 export revenue impact from CBAM-related market effects shows that even low-carbon generation can lose value when trade rules and corridor economics change. Add physical congestion to that regulatory pressure and the value gap becomes larger.
Bosnia and Herzegovina faces a different but equally serious constraint. Aging coal assets, delayed hydropower projects and fragmented institutional governance create uncertainty around future supply reliability. Projects such as HPP Dabar, HPP Mrsovo, Poklecani wind farm and Vlasic wind farm all illustrate the difficulty of moving from resource potential to bankable grid-connected capacity.
For investors, this changes due diligence priorities.
A renewable project in SEE can no longer be evaluated only by resource quality, EPC cost, permitting status and PPA price. Grid location is becoming a primary bankability variable. The key questions are now more specific: which substation, which voltage level, which congestion zone, which neighboring market, which curtailment probability, which balancing access, which cross-border spread, which TSO reinforcement timeline.
A 100 MW solar project with excellent irradiation but weak grid access may be less bankable than a smaller project near a strong transmission node with lower curtailment risk and better industrial offtake options.
This is a material shift in capital allocation.
The next generation of SEE renewable investment will likely favor projects that are designed around grid value rather than land availability alone. Developers that secured cheap land in weak-grid zones may face declining financing appetite. Developers with access to robust nodes, industrial consumers, storage integration and documented connection rights will command stronger valuation.
Banks will respond accordingly.
Lenders are likely to demand more detailed grid studies, TSO correspondence, curtailment scenarios, congestion sensitivity models, power-flow analysis, dispatch simulations and independent technical review before committing long-term debt.
This will also increase the value of Owner’s Engineer and technical advisory roles. Transmission risk is not easily understood through legal documentation alone. It requires integrated engineering, market and financial analysis.
The congestion decade will also reshape battery storage economics.
Storage is valuable not only because it shifts solar output from noon to evening. It is also valuable because it can reduce congestion at specific nodes, support grid stability and participate in balancing markets. The best storage locations will therefore be defined by network stress, not simply by co-location with generation.
This creates a new locational investment class: congestion-relief batteries.
A strategically placed battery near a constrained renewable cluster can generate revenue from arbitrage while also supporting grid reliability. In more advanced market designs, such assets may eventually receive regulated or semi-regulated compensation for grid services.
SEE is not yet fully there, but the direction is clear.
Transmission congestion also affects industrial policy. Industrial buyers exposed to CBAM will increasingly need traceable low-carbon electricity. But renewable electricity is only commercially useful if it can be delivered, documented and balanced. A factory cannot rely on a distant renewable asset if congestion prevents credible physical supply or hourly matching.
This means grid constraints may directly influence industrial relocation, export competitiveness and PPA bankability.
A CBAM-exposed manufacturer in Serbia or Montenegro will prefer renewable supply linked to credible network delivery paths, metering systems and balancing arrangements. Low-cost renewable generation stranded behind congestion will not solve the compliance problem.
This is why electricity-market congestion is becoming an economic development issue, not just a power-sector issue.
Governments across SEE will need to decide whether transmission investment remains a slow regulated utility function or becomes a strategic industrial policy priority. The difference will determine whether renewable capacity turns into export competitiveness or stranded production.
The most attractive future energy zones in SEE will likely combine four characteristics: strong renewable resources, robust transmission access, nearby industrial demand and storage potential. Areas with only one or two of those features may struggle to attract bankable capital.
Cross-border coordination will be equally important.
No single SEE country can solve congestion alone because the region’s electricity economics are corridor-based. Flows between Bulgaria and Greece, Serbia and Hungary, Romania and Hungary, Montenegro and Italy-linked markets, and Bosnia with Serbia and Croatia all interact. Reinforcing one national grid without aligning cross-border capacity can simply move congestion from one border to another.
The May data is therefore more than a short-term market snapshot.
It shows the early shape of a structural transition in which transmission becomes the central scarce asset. Generation remains essential, but grid access increasingly determines price capture, financing quality and strategic value.
The winners of the next decade will not necessarily be the countries with the most renewable megawatts.
They will be the countries that can move electrons efficiently, document their origin, balance their volatility and connect them to the highest-value consumers and export corridors.
Elevated by Energy.Clarion.Engineer