As South-East Europe navigates a transformative phase in its energy landscape, the integration of long-duration energy storage (LDES) is becoming essential for maintaining power system stability. The region has seen a significant uptick in renewable energy capacity, with installed wind and solar resources surpassing 34 GW by the end of 2025. This increase, which includes over 11 GW added in just four years, is primarily driven by Serbia, Romania, Greece, Croatia, and Bulgaria. Meanwhile, countries like Bosnia and Herzegovina, North Macedonia, and Montenegro are beginning to deploy utility-scale solar and wind projects that are expected to reshape their energy dynamics.
By 2030, projections indicate that variable renewable energy sources will contribute more than 45% of the region’s annual electricity generation, a dramatic rise from under 25% a decade ago. However, this rapid growth highlights vulnerabilities within existing power systems, particularly as flexibility resources remain predominantly reliant on conventional hydropower and thermal generation. While hydropower plays a critical role in countries like Serbia and Bosnia and Herzegovina, it is increasingly challenged by seasonal variability and hydrological uncertainties. Additionally, aging thermal fleets are under pressure from rising fuel costs and regulatory changes.
The limitations of short-duration batteries have become apparent as they provide only intraday balancing capabilities but cannot address multi-day renewable shortfalls. LDES systems—defined as those capable of delivering power for 8 to 72 hours or longer—are positioned to fill this gap effectively. System modeling suggests that by 2030, South-East Europe could face between 5–10 multi-day low-renewable events annually, where renewable output drops below 20% of installed capacity for over 48 hours. Currently, these deficits are managed through lignite use, gas imports, or emergency cross-border balancing—strategies that carry increasing economic risks.
The economic implications of LDES are significant. A single unit with a capacity of 1 GW / 24 GWh can replace approximately 1.3–1.6 GW of open-cycle gas turbines based on loss-of-load probability assessments tailored to South-East European load profiles. If each country were to deploy between 10–15 GWh of LDES capacity, it would enable most Western Balkan systems to manage critical multi-day deficits without relying on fossil fuel dispatch during peak periods—potentially reducing peak imports by 20–35%.
The stability benefits provided by LDES also extend to grid operations. The transmission networks in South-East Europe operate with lower inertia than those in Western Europe, particularly during high renewable output periods when thermal units are offline. This results in frequency fluctuations and voltage instabilities that impose costs on transmission operators through redispatch actions. Configured for grid services, LDES can deliver sustained frequency control and ramping capabilities over extended durations. Studies indicate that each gigawatt of LDES could lower annual balancing costs by €35–55 million by mitigating prolonged imbalance periods.
The integration of renewables further underscores the economic rationale for LDES adoption. In certain areas of South-East Europe, curtailment rates for utility-scale solar reach between 6–10%, primarily due to midday oversupply against limited export capacities. Although wind curtailment is less frequent on an annual basis, it can spike during extended high-wind conditions followed by grid congestion. By absorbing surplus generation over longer periods rather than just daily peaks, LDES can significantly reduce curtailment rates—modelling suggests that adding 1 MWh of LDES per 1.5–2 MW of solar capacity could decrease curtailment by over 60%.
The cross-border implications are also noteworthy as South-East Europe’s market remains partially coupled with limited interconnector utilization during stress events. Deploying LDES across jurisdictions can alleviate peak export and import pressures during critical hours while easing congestion across shared corridors. Coordinated deployment efforts totaling around 40–50 GWh could potentially reduce cross-border emergency flows by 25–30%, enhancing overall system resilience.
The demand from industrial sectors adds another dimension to the conversation around LDES implementation. Energy-intensive industries in Serbia, Romania, and Bulgaria face growing exposure to fluctuating power prices alongside carbon compliance costs. By utilizing long-duration storage solutions, these industrial consumers can shift their electricity demand towards economically advantageous stored renewable energy during deficit periods—potentially lowering annual procurement costs by between 8–12%.
Adequacy considerations further bolster the case for integrating LDES into regional power systems as many Western Balkan nations currently operate with reserve margins below 15%, limiting their ability to absorb outages or renewable shortfalls effectively. A strategic portfolio comprising around 5–7 GW of LDES by 2035, could facilitate the retirement or reduced operation of at least 3–4 GW of inefficient thermal capacity while simultaneously cutting emissions by approximately 6–9 million tonnes of CO₂ annually.
The barriers hindering the widespread adoption of long-duration storage technologies are largely structural rather than technical; these systems often remain overlooked in national adequacy assessments and regulatory frameworks across the region. Revenue models tend to be fragmented while permitting processes frequently treat storage as secondary infrastructure rather than essential components for stability enhancement.
Cumulatively addressing the flexibility gap in South-East Europe necessitates an investment ranging from €18 billion to €25 billion in long-duration storage solutions by 2040. This financial commitment parallels the ongoing maintenance costs associated with aging thermal fleets but promises vastly improved outcomes concerning emissions reduction and enhanced security of supply.
The implementation of long-duration energy storage thus represents a pivotal shift for the power systems across South-East Europe; it enables the transition from dependence on volatile renewables towards a more controllable resource base while redefining grid stability from a challenge into a service-oriented solution.
