Rapid battery deployment across Southeast Europe is expected to narrow the price spreads that support merchant arbitrage and lower prices for some balancing services. This raises the bar for long-term projects, as investors need revenue models that account for storage competition. Those models must remain viable if current arbitrage and ancillary-service prices fall materially.
Bulgaria’s storage fleet is estimated to exceed 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 as of 1 October, although the year was not specified. Hungary’s grid-scale storage capacity has surpassed 1 GW.
In Greece, the 330 MW / 790 MWh Larissa BESS in Thessaly was commissioned 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 state that the Thessaloniki project has been commissioned.
Battery deployment reshapes price spreads and balancing markets
Batteries charge during low-price hours, adding demand, and discharge during high-price hours, adding supply. As more capacity operates, it can make midday price troughs less pronounced and evening peaks less extreme. That can squeeze the spread between solar-heavy midday hours and evening demand peaks. The regional fleet is developing quickly enough to change the price curve within a single investment cycle.
Balancing services face a separate source of pressure: 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. However, investors need to test revenue assumptions against reductions in both arbitrage capture and ancillary-service prices.
Investment cases account for operating strategy and future spreads
Project design and operating strategy can create value beyond standalone arbitrage. Four- or five-hour batteries can compete in different time windows from one- or two-hour systems. Co-location with renewable generation can reduce curtailment and support shaped power purchase agreements, while industrial batteries can monetise demand optimisation and resilience. Portfolio batteries can also improve a trader’s imbalance position as standalone arbitrage margins shrink.
Projects entering service in 2028 or 2029 should not be valued using 2026 price spreads, according to the investment guidance in the regional outlook. The market is shifting from first-mover economics towards operating excellence. Long-term battery storage investment models that assume some erosion of current arbitrage opportunities are central to a credible investment case.