Title: Vattenfall Approves 1 GWh Brunsbüttel Battery at Former Nuclear Site

Vattenfall has taken a final investment decision to build the Vattenfall Brunsbüttel battery at the site of the former Brunsbüttel nuclear power plant in northern Germany, moving the project from planning into an approved investment. The company announced the decision on September 10 and now expects the battery and a new grid-connection substation to be operating by the end of 2028.

The standalone system is planned at 254 MW with up to 1,000 MWh of storage, about four hours of energy at its rated output. That is 300 MWh more storage than Vattenfall described when Brunsbüttel’s city council approved the project’s development plan in December 2025, while the 254 MW power rating remains unchanged.

Final investment decision clears a key project hurdle

Vattenfall’s September 10 project announcement says the company will build the battery on the decommissioning nuclear-plant site and connect it to the 50Hertz 380 kV transmission system. Vattenfall describes it as its largest battery project to date.

The investment decision is materially different from the project’s earlier milestones. In December 2025, Vattenfall said the city council had approved the development plan, but construction remained subject to a final investment decision. A Schleswig-Holstein environmental notice later recorded a June 2026 permit for a substation and battery installation.

Independent reporting by pv magazine Deutschland also confirmed the final investment decision and noted that the energy capacity has increased from the previously announced 700 MWh to 1,000 MWh.

The battery is larger in energy capacity than the 2025 plan

The revised configuration keeps the project’s power rating at 254 MW while increasing storage capacity by roughly 43% from 700 MWh to 1,000 MWh. At the stated ratings, dividing energy capacity by maximum power gives a duration of about 3.9 hours. The precise usable duration can differ from that simple ratio depending on operating limits and system design.

Vattenfall has not disclosed the battery supplier, chemistry, construction cost or expected annual dispatch profile in the current announcement. Those details remain important for assessing the project’s economics and technical configuration.

Brunsbüttel reuses a major power-system location

The Vattenfall Brunsbüttel battery is planned on the grounds of a nuclear station that has been permanently shut since 2007 and is being dismantled. The site retains access to high-voltage transmission infrastructure, making the project another example of new flexible resources being developed at legacy power sites.

Microgrid Media has separately examined how batteries can use existing power-plant interconnection capacity to reduce some of the grid-connection barriers facing new resources. The regulatory structure in Germany is different from PJM’s, but the underlying infrastructure question is similar: established power sites can have valuable land and grid access after the original generating asset closes.

Vattenfall says its current battery portfolio comprises 150 MW in operation and 120 MW under construction. The company expects the new Brunsbüttel project, once operating, to nearly double its owned battery power capacity.

What happens next

The final investment decision means the project has advanced beyond the conditional planning stage, but the battery is not yet operating. Vattenfall still has to build the storage facility and new substation, complete the transmission connection and commission the system.

If the current schedule holds, the Vattenfall Brunsbüttel battery will enter service by the end of 2028 with 254 MW of power and up to 1,000 MWh of energy capacity. Construction progress, equipment selection and commissioning will be the next independently verifiable milestones.