Rapid battery deployment across Southeast Europe is expected to compress merchant-arbitrage spreads and lower prices for some balancing services, raising revenue risks for long-term projects. The regional outlook says storage models must test whether returns remain acceptable after material reductions in arbitrage capture and ancillary-service prices.
Latest estimates put Bulgaria’s storage fleet above 6.2 GW of power capacity and 19 GWh of energy capacity. Romania had 1,162 MW of storage power capacity and 2,312 MWh of storage energy capacity at 1 October; the year was not specified. Hungary has moved above 1 GW of grid-scale storage capacity.
Greece commissioned the 330 MW / 790 MWh Larissa BESS in Thessaly in October 2026. A separate 100 MW / 200 MWh battery project is located at HELLENiQ ENERGY’s facilities in Thessaloniki; the available information does not say it has been commissioned.
Competition changes market revenues
Batteries charge during low-price hours, increasing demand, and discharge during high-price hours, adding supply. As deployment grows, that activity is expected to make midday price troughs less deep and evening peaks less extreme, squeezing the spread between solar-heavy midday hours and evening demand peaks. The regional fleet is being built quickly enough to change the price curve within a single investment cycle.
Balancing markets face a separate risk: relatively small amounts of fast-response capacity can saturate high-value services and push clearing prices lower. A narrower spread does not necessarily make new storage uneconomic, but it changes what investors need to model.
Investors look beyond standalone arbitrage
Long-term battery energy storage system models should assume competing storage will erode part of today’s arbitrage opportunity. A credible investment case requires revenues to remain acceptable after a material reduction in both arbitrage capture and ancillary-service prices. Projects entering service in 2028 or 2029 should not be valued using 2026 price spreads.
Project duration and configuration can open different revenue opportunities. Four- or five-hour batteries can compete in different time windows from one- or two-hour systems. Batteries co-located with renewable generation can reduce curtailment and earn value through shaped power purchase agreements, while industrial systems can monetise demand optimisation and resilience.
Portfolio batteries can improve a trader’s imbalance position even when standalone arbitrage margins shrink. The market is shifting from first-mover economics toward operating excellence, making revenue diversification and competition assumptions central to long-term project models.