TagEnergy and Banque des Territoires officially opened France’s largest operating battery facility on October 1. Creating a new example of grid-scale energy storage studies, the Cernay-lès-Reims facility offers 240 MW power and 480 MWh energy capacity. The facility has been operating commercially since May; The event in October marks the official opening.
The project in the Marne region is connected to RTE’s 225 thousand volt electricity transmission network. In addition, there are 140 battery containers in an area exceeding approximately three hectares. Partners use the system to contribute to the stability of the network with frequency and voltage regulation services.
The values 240 MW and 480 MWh here describe different features. The power value shows the transfer capacity at a certain moment, and the energy value shows the total amount that can be stored. When we divide the nominal values we get approximately two hours; The actual operating time depends on the load, available energy and operating conditions.
For this reason, the facility should not be treated as a production power plant that constantly provides electricity to the same number of homes. The battery stores the energy produced by other sources and returns it when needed. Thus, it can provide flexibility to the electricity system in the face of concentration of production and consumption at different times.
Battery plant contributes to frequency and voltage regulation
According to PV Magazine’s project information, the installation uses Tesla Megapack battery systems. The facility completed the necessary simulation, testing and certification stages before starting network services. Eiffage handled the construction and electrical works, and Tewa Solar provided project support from development to commissioning.
Initial operating results cited by TagEnergy show that 70.5 GWh of energy was returned to the grid in four months. In addition, the company states that it completed 145 full cycles in a 125-day period. These figures provide information about the usage of the storage system; It does not refer to new energy production such as solar or wind power plants.
Banque des Territoires participated in the project with a 49 percent share in 2025; TagEnergy remained the majority shareholder. The facility also marks the first joint investment of the two organizations in their three-year partnership. In addition, the partnership aims to support the financing of other large battery projects in France.
The financing was provided by the banking group consisting of ABN AMRO, NORD/LB and Caisse d’Épargne CEPAC. On the other hand, the official statement does not announce a separate electricity tariff or household subscription service for consumers. The direct function of the project is to respond to the balancing need in the transmission network by using the stored electricity when necessary.