Battery investment and rising intraday trading are expanding flexibility markets across Southeast Europe, while growing competition is beginning to narrow the exceptional returns available to early projects. Bulgaria is the most advanced market in the region, where storage operators can trade energy and provide system services at scale.
The IBEX intraday continuous market recorded 1.432 TWh of trading in October, its highest volume to date. Bulgaria’s battery fleet exceeds 6.2 GW of power capacity, allowing operators to buy energy, rebalance positions and provide system services. As more storage enters the market, competition is starting to reduce the exceptional revenues available to the earliest battery projects.
Croatia commissioned the Šibenik battery energy storage system on 4 November. The system has 60 MW of power capacity and 120 MWh of energy capacity, is connected at 110 kV and is integrated into HOPS’s automatic frequency restoration reserve framework. The project establishes a commercial and regulatory precedent for standalone storage on Croatia’s transmission system.
Romania is developing the region’s next large storage market. October figures put its battery energy storage system capacity at about 1.16 GW of power and 2.31 GWh of energy, with a project pipeline exceeding 9 GW. Greece has around 800 MW of storage connected and is using it to reduce renewable energy curtailment.
As these markets expand, cross-border balancing and intraday integration are expected to become more valuable. Local flexibility can be exported economically only where market rules and transmission capacity allow electricity to move across borders.
The Agency for the Cooperation of Energy Regulators (ACER) said its 2026 market-integration work shows day-ahead markets have largely moved to 15-minute products, while access to cross-zonal capacity remains weaker in intraday and balancing timeframes. Congestion-management costs reached 5.4 billion euros in 2025, strengthening the case for flexible assets and rules that enable electricity to move across time and space.
Battery financing needs to account for multiple accessible revenue sources and the risk of increasing competition for each. Energy arbitrage, balancing, renewable optimisation and contracted services should be assessed against the same physical operating limits.