Vattenfall has taken FID on a 254 MW battery at a decommissioned German nuclear site — but the number that changed since permitting isn’t the one you’d expect.
Vattenfall has taken the final investment decision on a 254 megawatt battery at Brunsbüttel, the north German town whose nuclear power plant the company has been dismantling since 2019. The battery will sit on land freed up by that decommissioning, connect into 50Hertz’s transmission grid, and is due online by the end of 2028 — one of the largest single battery storage projects announced in Germany this year, and Vattenfall’s biggest to date.
What’s easy to miss in that headline figure is how much it moved. When Brunsbüttel’s city council approved the development plan back in December 2025, the project was pitched at the same 254 MW output paired with 700 MWh of storage — a roughly 2.75-hour system. Nine months later, at FID, the power rating hasn’t budged, but the energy capacity has grown by more than 40%, to “up to 1,000 MWh,” pushing the battery toward a full four-hour design.
That shift tracks a broader repricing across German battery economics. Modo Energy’s 2026 investment outlook finds that a four-hour battery entering service in Germany this year is now expected to outperform a two-hour system on returns — a 13.7% unlevered IRR versus 12.2% — despite costing roughly a third more to build. The reason is where the revenue is coming from: frequency-regulation markets (FCR and aFRR) made up more than half of German battery income this year, but that market caps out around a combined 4.5 GW of capacity. As more batteries chase the same pool, those returns compress, and operators fall back increasingly on day-ahead and intraday trading — arbitrage that a longer-duration battery is simply better built to capture. Brunsbüttel’s extra 300 MWh looks less like scope creep than a developer re-sizing for where the money is actually going to come from.
“Batteries play a key role in the future energy system, balancing electricity demand and supply,” said Claus Wattendrup, Vattenfall’s head of solar and batteries. “As generation from solar and wind power continues to grow, powerful storage solutions are essential for strengthening energy security and reducing dependence on fossil fuel imports.”
Brunsbüttel will roughly double Vattenfall’s owned battery capacity, which currently stands at 150 MW in operation and 120 MW under construction, much of it co-located with wind and solar sites. The company is also building a separate business optimising batteries it doesn’t own on behalf of third-party asset holders, and is targeting a managed portfolio of up to 1,500 MW by 2029.
The timing points to a second story sitting underneath this one. Vattenfall’s own announcement cites transmission operators’ expectation that large-scale battery storage will exceed 80 GW by 2040 — but that figure is already looking conservative. Germany’s four transmission system operators opened public consultation on September 1 on a new joint planning scenario that puts 2040 battery capacity at 84.1 to 102.4 GW, roughly double the low end of their previous range. Official assumptions about how much storage the grid will need keep getting revised upward faster than individual projects like Brunsbüttel can be built — which may be the more durable story behind this week’s announcement.
