The energy landscape in Southeast Europe is undergoing a significant transformation as the growth of renewable energy capacity begins to exceed the capabilities of existing transmission networks, which were designed decades ago. This transition is particularly evident in the Western Balkans, where a historical reliance on synchronous thermal generation, primarily from large lignite plants, is giving way to an increasing share of inverter-based renewable sources like wind and solar. This shift raises concerns about grid stability and has prompted transmission system operators to explore new ancillary services markets and flexibility mechanisms.
The traditional power infrastructure in the region has been heavily reliant on coal-fired generation. Major plants such as Serbia’s Nikola Tesla A and B, Bosnia and Herzegovina’s Tuzla and Kakanj, Bulgaria’s Maritsa East lignite basin, and Romania’s Oltenia lignite facilities have collectively provided substantial synchronous capacity. These plants utilize heavy rotating turbines that help stabilize grid frequency by slowing down frequency deviations during supply-demand imbalances.
In contrast, wind and solar installations connect to the grid through power electronics rather than rotating machinery. As a result, while they contribute energy to the grid, they offer limited natural inertia unless equipped with advanced grid-forming inverter technologies. The increasing penetration of these inverter-based resources alters the dynamic stability characteristics of the electricity system.
The renewable energy pipeline across Southeast Europe is expanding rapidly. Serbia has initiated auction rounds aiming for approximately 1.3 GW of new wind and solar capacity, while private projects in various stages exceed 4 GW. Romania’s renewable development pipeline has surpassed 15 GW, bolstered by contracts for difference schemes and heightened investor interest. Bulgaria is witnessing unprecedented growth in solar capacity, with several gigawatts of photovoltaic projects either connected or awaiting grid approval. Montenegro is also advancing projects like the 54.6 MW Gvozd wind farm alongside additional solar initiatives linked to its state utility.
These developments are reshaping the generation mix significantly. During peak solar output periods, some Balkan markets report renewable generation exceeding 50% of instantaneous demand, particularly in spring and summer when hydropower production also peaks. This scenario heightens sensitivity to frequency disturbances due to a diminished contribution from synchronous machines.
Transmission system operators—including EMS in Serbia, CGES in Montenegro, ESO in Bulgaria, and Transelectrica in Romania—are grappling with a structural decline in system inertia. Engineers increasingly refer to this challenge as a shift from an “energy problem” to a “system services problem.” The core issue lies not with the electrons generated but rather with maintaining frequency stability, voltage support, and flexibility as traditional baseload plants operate at reduced levels.
The consequences of this transition are already visible within balancing markets. The value of frequency containment reserves and automatic frequency restoration reserves is rising as operators seek quicker responses to stabilize their systems. Battery energy storage systems are emerging as pivotal assets capable of responding within milliseconds to provide necessary services.
In Central Europe, ancillary services markets have become an essential revenue source for storage developers; similar trends are beginning to emerge across Southeast Europe. Analysts project that balancing and frequency services across the Balkan region could yield an annual market value exceeding €300 million by 2030—dependent on renewable penetration rates and market design reforms—indicating a significant shift in electricity system economics.
Battery storage projects are proliferating throughout the region. Bulgaria has launched a national initiative promoting gigawatt-scale battery deployment funded by European recovery funds. Romania is approving storage facilities linked to renewable projects while Serbia develops regulatory frameworks for storage participation in electricity markets alongside upcoming solar installations. Montenegro is also evaluating storage integration within its broader renewable strategy.
Pumped hydro storage continues to be a critical flexibility resource within this evolving landscape. Serbia’s planned Reversible Hydropower Plant Bistrica will have an anticipated capacity of approximately 600 MW designed specifically for renewable integration by absorbing excess electricity during high production periods and releasing it during demand peaks—essential for providing multi-hour storage and system inertia.
As ancillary services markets gain prominence within Southeast Europe’s electricity economics, developers are increasingly looking beyond traditional energy sales toward revenue opportunities from balancing services and grid stabilization mechanisms involving batteries, pumped hydro facilities, and flexible gas turbines.
This transition necessitates regulatory evolution; historically characterized by vertically integrated utilities and bilateral contracts, Balkan electricity markets must adapt toward more dynamic balancing frameworks akin to those found in Western Europe—encompassing shorter gate closure times for intraday markets and enhanced cross-border cooperation among transmission operators.
Another critical technological advancement involves deploying grid-forming inverters that enable renewable plants or battery systems to emulate synchronous generator behavior by providing synthetic inertia and frequency support—a technology expected to become standard as system operators tighten grid code requirements.
The implications of this transition extend beyond mere capacity expansion; they signal an engineering phase requiring substantial investments not only in renewables but also in essential infrastructure such as storage solutions, grid reinforcements, digital monitoring systems, and sophisticated market mechanisms necessary for ensuring reliability amidst growing renewable integration.
As Southeast Europe’s ancillary services market emerges as a new frontier within its electricity sector dynamics, developers who effectively combine renewable generation with storage or flexibility assets may find opportunities for additional revenue streams while mitigating curtailment risks. Utilities must adapt their operational frameworks accordingly to manage an increasingly complex grid environment.
The declining inertia represents both challenges regarding technical operations as well as economic opportunities within this transforming landscape; with rising renewable penetration rates enhancing the value of fast-response flexibility assets like batteries and pumped hydro facilities becoming integral components of regional electricity systems.
