Across Southeast Europe, solar-heavy midday electricity is increasingly becoming a feedstock for storage operators, who buy power and shift it for sale in later hours when the system values it more highly. Some output that was low-value or unwanted surplus is becoming a source of demand for batteries. Operators lose part of the electricity through battery efficiency losses before selling the remainder.
Bulgaria is the region’s most advanced example of the shift. The country had around 7.2 GW of installed solar capacity by October, and photovoltaic generation reached 1,165 GWh in August 2026. Its battery fleet exceeds 6 GW, creating a large structural source of demand during solar-generation hours.
Battery operators are becoming buyers of midday electricity alongside industrial consumers and exporters. They use storage to shift electricity from one time of day to another, buying during solar-heavy hours and selling the remaining power later when it is valued more highly. Battery efficiency losses reduce the amount available for later sale.
Serbia is at an earlier stage of the shift but has begun recording negative electricity prices. SEEPEX allowed negative prices from May 2026, and Serbia recorded its first negative day-ahead price hour on 10 May. Such prices can give storage operators a potentially negative acquisition cost for surplus electricity.
Negative-price hours should not be treated as a constant feature of project economics. As battery demand grows, it is expected to put a floor under some of the deepest solar-price collapses, but the supplied facts do not establish that such demand will remove price volatility.
Renewable developers can capture value by co-locating storage with generation and retaining the time-shifting margin. Instead of selling the cheapest hours to an external storage operator, they can store some generation and sell it later. This approach lets developers retain that margin as battery operators increasingly buy midday electricity across the region.
