The electricity landscape in Southeast Europe is undergoing a significant transformation as the integration of renewable energy sources accelerates. This shift is particularly pronounced in the Western Balkans, where traditional power systems, historically reliant on coal-fired generation, are adapting to the increasing prevalence of wind and solar energy. The challenge lies not merely in the deployment of renewables but in addressing the operational implications of replacing synchronous thermal generation with inverter-based technologies.
Historically, the Balkan power system has been anchored by large lignite plants, such as Serbia’s Nikola Tesla A and B, Bosnia and Herzegovina’s Tuzla and Kakanj complexes, Bulgaria’s Maritsa East lignite basin, and Romania’s Oltenia plants. These facilities provided substantial synchronous capacity through heavy rotating turbines that stabilize grid frequency. In contrast, wind and solar installations connect to the grid via power electronics, offering limited natural inertia unless equipped with advanced grid-forming inverter technologies.
The rapid expansion of renewable projects is reshaping the generation mix across the region. For instance, Serbia has initiated auction rounds aimed at adding approximately 1.3 GW of new wind and solar capacity, while private projects in various development stages exceed 4 GW. Romania’s renewable pipeline has surpassed 15 GW, bolstered by contracts for difference schemes. Bulgaria is witnessing a solar boom with several gigawatts of photovoltaic projects either connected or pending approval. Montenegro is also advancing its renewable agenda with initiatives like the 54.6 MW Gvozd wind farm.
As these developments unfold, the share of renewable generation can exceed 50% during peak solar hours in some markets, particularly in spring and summer when hydropower output is also high. This increased reliance on inverter-based generation heightens sensitivity to frequency disturbances due to a diminished proportion of synchronous machines contributing to stability.
Transmission system operators—including EMS in Serbia, CGES in Montenegro, ESO in Bulgaria, and Transelectrica in Romania—are now facing a structural decline in system inertia. The transition from an “energy problem” to a “system services problem” reflects the need for enhanced frequency stability and voltage support as traditional baseload plants operate at reduced levels.
The operational impacts are evident in balancing markets where demand for frequency containment reserves and automatic frequency restoration reserves is rising. Battery energy storage systems are emerging as crucial assets capable of responding within milliseconds to stabilize the grid.
In Central Europe, ancillary services markets have become vital revenue streams for storage developers. Similar trends are beginning to materialize in Southeast Europe, where market analysts project that balancing and frequency services could generate an annual market value exceeding €300 million by 2030, contingent on renewable penetration levels and necessary market reforms.
Battery energy storage initiatives are proliferating throughout the region. Bulgaria has launched a national program for gigawatt-scale battery deployment supported by European recovery funds. Romania is approving storage facilities linked to renewable projects while Serbia prepares regulatory frameworks to facilitate storage participation in electricity markets. Montenegro is also considering storage integration within its broader renewable strategy.
Pumped hydro storage remains a key flexibility resource; for example, Serbia’s planned Reversible Hydropower Plant Bistrica aims to provide approximately 600 MW capacity to absorb excess electricity during high production periods and release it during peak demand.
The evolution of ancillary services markets signifies a shift towards more dynamic electricity system economics in Southeast Europe. Asset developers are increasingly focused on revenue from balancing services rather than relying solely on energy sales from day-ahead markets. Technologies such as batteries, pumped hydro facilities, and flexible gas turbines are poised to capitalize on this operational flexibility.
Regulatory frameworks must also evolve to accommodate these changes. Historically characterized by vertically integrated utilities and bilateral contracts, Balkan electricity markets require more dynamic balancing frameworks akin to those found in Western Europe. This includes adopting shorter gate closure times for intraday markets and enhancing cross-border cooperation among transmission operators.
Technological advancements like grid-forming inverters are gaining traction as they enable renewable plants or battery systems to emulate synchronous generators by providing synthetic inertia and frequency support. As these technologies become standard in future projects, they will play a crucial role in maintaining grid stability.
The ongoing transition marks a complex engineering phase for the Balkan energy sector. The focus is shifting from merely expanding generation capacity to effectively integrating this capacity into existing systems without compromising reliability. Investments will be necessary not only in renewables but also in storage solutions, grid enhancements, digital monitoring systems, and advanced market mechanisms.
The declining system inertia presents both challenges and opportunities within the evolving landscape of Southeast European electricity markets. As renewable penetration increases, the demand for fast-response flexibility assets will rise correspondingly. Technologies such as batteries and pumped hydro plants will become integral components of regional electricity systems as stakeholders adapt to this new paradigm.
