Battery investment and intraday trading are expanding flexibility markets across Southeast Europe, with Bulgaria’s battery fleet exceeding 6.2 GW and its intraday market recording October trading of 1.432 TWh. Growing activity creates more ways for storage operators to earn revenue, but competition is beginning to reduce the exceptional returns available to the earliest projects.
Bulgaria is the region’s most advanced market. The IBEX intraday continuous market’s October volume was its highest to date, allowing operators to buy energy, rebalance positions and provide system services at scale. As more batteries compete for these opportunities, financing needs to account for the potential for revenue sources to become more contested.
In Croatia, the Šibenik battery energy storage system was commissioned on 4 November. The 60 MW, 120 MWh installation is connected at 110 kV and integrated into HOPS’s automatic frequency restoration reserve framework. It establishes a commercial and regulatory precedent for standalone storage in Croatia’s transmission system.
Romania is developing the next large storage market, with about 1.16 GW of battery power capacity and 2.31 GWh of energy capacity reported for October. Its project pipeline exceeds 9 GW. Greece has around 800 MW of storage connected and is using it to reduce renewable energy curtailment.
Market access shapes storage revenues
As regional markets scale, 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 permit it, limiting the revenue opportunities available to storage operators.
The Agency for the Cooperation of Energy Regulators (ACER) said its 2026 market-integration work found that day-ahead markets had largely moved to 15-minute products, while access to cross-zonal capacity remained 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 allow electricity to move across time and space.
Battery financing should assess energy arbitrage, balancing, renewable optimisation and contracted services as separate accessible revenue sources, while accounting for increasing competition for each. Each source must also be assessed against the same physical operating limits of the battery.