South-East Europe’s grid overhaul shifts the bottleneck from generation to transmission corridors

South-East Europe’s electricity system is entering a decisive phase in which transmission infrastructure—not generation capacity—is becoming the primary constraint and the key determinant of value. As renewables scale up across the Western Balkans, investors are finding that where power can physically move through the grid may matter as much as how much renewable capacity is installed.

A corridor-based architecture replaces isolated national systems

The shift underway is not simply an expansion of supply. It represents a structural reconfiguration of how electricity moves across the region, moving away from a traditional model in which national systems operated largely in isolation with limited cross-border exchange. In its place is an emerging corridor-based design anchored in high-voltage transmission and increasingly shaped by renewable generation patterns.

At the center of this transformation is the Trans-Balkan electricity corridor, which is evolving into a regional backbone rather than remaining a single project. Announcements spanning 2025 to 2026 indicate it is being developed as a multi-country infrastructure platform linking Serbia and Montenegro with Bosnia and Herzegovina and extending toward EU markets.

400 kV investments aim to unlock cross-border transfers—and relieve congestion

The next phase of development is defined by interconnected 400 kV projects intended to increase transfer capacity and support larger electricity exchanges. A double 400 kV overhead line linking Pljevlja in Montenegro, Bajina Bašta in Serbia, and Višegrad in Bosnia and Herzegovina is designed to complete the core Trans-Balkan loop. The plan also includes enabling flows toward Italy through an existing submarine cable.

Additional interconnections—including Gacko–Brezna (Bosnia and Herzegovina–Montenegro) and Brezna–Sarajevo 400 kV links—are being advanced to reduce congestion and support renewable integration across western Balkan systems. The projects are explicitly framed as infrastructure that can absorb rising wind and solar volumes, particularly in mountainous and coastal areas where grid capacity has historically lagged development potential.

Further east, the Kosovo–North Macedonia 400 kV corridor is emerging as part of a broader east–west transmission axis, strengthening connectivity toward Albania and supporting a more balanced regional dispatch structure. Albania’s own grid transformation—new 400 kV interconnections with Kosovo and Greece alongside upgrades to substations such as Fierza—is positioned within this wider effort, with the country described as moving toward a future renewable export role.

Storage becomes part of the transmission equation

Transmission buildout alone is not presented as sufficient for renewables growth. The article points to system flexibility as an increasingly necessary complement to stronger interconnections, highlighting that variability requires both time-shifting capability and corridor capacity to prevent congestion from undermining integration.

A key project cited is the proposed Moglice pumped-storage expansion in Albania, described as having up to 1,620 MW of capacity and around 30 GWh of storage. If developed, it would provide balancing capability across multiple national systems—an explicit recognition that flexibility needs to be built alongside network reinforcement.

Renewable pipelines are increasingly tied directly to grid constraints

The link between transmission investment and renewable development is becoming more explicit in project design. In northeastern Albania, new 400 kV infrastructure is being planned specifically to enable integration of more than 1 GW of wind capacity while also relieving pressure on existing 220 kV lines.

Montenegro provides another example: a developing partnership between EPCG and Masdar targets large-scale solar, wind, and hybrid projects with an objective of exporting green electricity through Montenegro’s existing interconnection with Italy. In this framing, transmission capacity functions as a monetisation channel for renewables rather than a passive asset.

Serbia reinforces internal bottlenecks while replacing aging assets

Serbia remains described as the central node within this evolving network. Its internal grid—particularly its 400 kV network linking Belgrade, Kragujevac, Kraljevo and Niš—is being reinforced with investments estimated at EUR 200–300 million. The stated aim is reducing internal bottlenecks and improving north–south transfer capacity.

New lines such as Kragujevac–Kraljevo and Obrenovac–Bajina Bašta are also being constructed to replace aging 220 kV infrastructure and strengthen Serbia’s role as a regional transit hub.

Legacy voltages still constrain real-world outcomes

Despite acceleration at higher voltage levels, the broader system remains constrained by legacy infrastructure. The article highlights that the 220 kV network—still widely used across SEE—is increasingly identified as a bottleneck. It cites rehabilitation work on the Trebinje–Perućica–Podgorica–Vau Dejës corridor as an example of efforts needed simply to maintain operability under higher load and greater renewable penetration.

At 110 kV level, constraints are described as even more acute because many renewable projects connect there. Congestion, transformer limitations and local network constraints can determine real output levels; without reinforcement at these lower voltages, expanded high-voltage corridors may not translate into effective delivery from generation sites.

A “three-speed” grid shapes market behavior

The result described is a three-speed grid: expanding integration at 400 kV; selective rehabilitation stabilizing parts of the 220 kV layer; and increasing stress at 110 kV driven by decentralised generation. This layered dynamic influences not only physical flows but also market behavior.

Electricity markets across SEE are beginning to reflect these structural realities. Cross-border capacity expansions are increasing trading volumes and reducing price spreads in well-connected corridors—particularly between Serbia and Hungary or Romania—while congestion persists elsewhere, contributing to persistent regional price divergence and arbitrage opportunities.

The article also points to negative pricing mechanisms and expanding balancing markets as factors accelerating change. As price signals become more granular and more reflective of physical constraints, weaknesses in parts of the network become more visible—and flexibility becomes more valuable economically. Storage options, hybrid generation models, and proximity to strong transmission nodes are highlighted as emerging determinants of project economics.

By mid-decade: interconnected corridors without full market convergence

Looking ahead to 2030–2035, South-East Europe is unlikely to converge into a fully unified electricity market comparable with Western Europe. Instead, it suggests an interconnected transmission landscape coexisting with local bottlenecks and uneven investment conditions.

The article describes three investment geographies taking shape: a northern belt linking Hungary, Romania and northern Serbia where strong interconnections support relatively stable conditions; a transitional central layer including Serbia’s internal grid plus parts of Bosnia (and Bulgaria mentioned) where reinforcement continues but remains incomplete; and a southern or western periphery including Albania, Montenegro and parts of North Macedonia where large renewable potential emerges alongside still-developing transmission infrastructure.

Transmission corridors become economic arteries for capital allocation

Taken together, these developments suggest that South-East Europe is moving from fragmented national systems toward a corridor-driven regional market where transmission infrastructure, renewable generation plans and storage capability are tightly linked. For investors evaluating renewables across SEE now—and through the next phase—the value proposition increasingly depends on network position: access to 400 kV corridors, exposure to congestion risk at lower voltages, and whether flexibility can be integrated alongside generation growth.