Bulgaria is leading Southeast Europe’s shift of solar-hour electricity into storage, with its battery fleet exceeding 6 GW. Serbia is also beginning to record negative prices as solar-heavy midday supply is increasingly bought and moved to later hours. This allows some surplus generation to be stored instead of being sold when it has little or no value.
Batteries absorb midday solar supply
Bulgaria had around 7.2 GW of installed solar capacity by October, and photovoltaic generation reached 1,165 GWh in August 2026. The battery fleet in the country creates a large, structural source of demand during solar-generation hours. Storage operators buy electricity in the middle of the day, absorb some losses through battery inefficiency and sell the remaining power later, when it is valued more highly.
Alongside industrial consumers and exporters, storage operators are becoming buyers that shift electricity between times of day. As battery demand grows, it is expected to put a floor under some of the steepest solar-price declines. Renewable developers can also capture value by co-locating storage with generation, keeping the time-shifting margin instead of selling the cheapest hours to an external storage operator.
Serbia records its first negative day-ahead price
SEEPEX began allowing negative prices in Serbia in May 2026, and the first negative day-ahead price hour occurred on 10 May. Such prices can give storage operators a potentially negative acquisition cost for surplus electricity. However, negative-price hours should not be treated as a constant feature of project economics.
