Near Reims, France's Largest Battery Is Inaugurated

On a three-hectare site near Reims, 140 Tesla Megapacks now form the largest electricity storage battery in mainland France. It has just been inaugurated, with a power rating of 240 MW and a capacity of 480 MWh. Construction took just fifteen months.

The problem this installation addresses is simple to state and hard to solve. Solar power is produced mainly during the day, while demand often peaks in the evening. The grid must therefore absorb production that does not coincide with needs. The battery acts as a buffer: it captures electricity when there is plenty, then releases it when the grid needs it most. This is precisely what the new installation is meant to allow RTE, the transmission system operator, to exploit better than before.

The size of the facility matters, but so does its flexibility. RTE can call on this battery at any time to continuously balance consumption and production, but also to help regulate voltage and frequency, which keep the current within expected limits. Before it, the largest installation of this kind was in Nantes, with 200 MWh, commissioned by Harmony Energy in August 2025. The gap is clear, but it is measured above all in operating hours: as of September 23, the battery had completed 145 charge and discharge cycles in 125 days and fed more than 70 GWh of electricity back into the grid. These figures come from the operator and were published at the inauguration; they have not yet been checked against an independent measurement, and several more months of data will be needed to assess their consistency.

For RTE, the benefit lies less in the advertised power than in availability: equipment that can be called upon at any moment, in the evening or in the middle of the night, becomes a grid-regulation tool on a par with a power plant. For the partners, TagEnergy and Banque des Territoires, the facility is a starting point. They have signed a three-year agreement to fund several other storage installations in France, although the number and timing of these projects have not been specified at this stage. The next step will therefore be judged on projects yet to come, and on whether this model can be replicated elsewhere in the country.