The largest energy storage facility in France has been commissioned
In August 2025, the largest battery energy storage system in France was energized at the port of Nantes-Saint-Nazaire.
The Cheviré project was developed by British company Harmony Energy. The installation has a total power output of 100 MW and a capacity of 200 MWh.
Cheviré: From Fossil Fuels to Clean Energy
The system was built on the site of the former Cheviré power plant, which operated between 1954 and 1986 and used coal, gas, and oil. Its location next to transmission operator RTE’s substation enables optimal integration with the national grid at a charging and discharging voltage of 63 kV.
Cheviré is a two-hour energy storage facility. This means that at full charge it can deliver 100 MW of power for two hours, supplying electricity to about 170,000 households—more than the population of Nantes itself.
Tesla Megapack and Autobidder
Harmony Energy deployed containerized Tesla Megapack batteries equipped with the Autobidder energy management system. This solution allows for dynamic optimization of charging and discharging depending on market conditions and grid needs. The system’s lifetime is estimated at 15 years, with the potential for extension through technological upgrades.
Construction began in the summer of 2024, and within one year the project reached the energization phase. Full commercial operation is expected by the end of 2025.
“The Cheviré project demonstrates how knowledge, experience, and teamwork can accelerate the transition to a zero-emission energy system,” emphasized Andy Symonds, Director of Harmony Energy France.
Environmental and Social Aspects
The investment is not just about technology. Harmony Energy states that the project also includes measures for biodiversity and local communities, funded in part through a social benefits fund. Such initiatives help strengthen public acceptance and ensure the smooth integration of large infrastructure projects with their surroundings.
Harmony Energy is one of Europe’s leading BESS developers. In addition to Cheviré, the company delivered the Bumpers system in the UK (198 MWh), which until recently was Europe’s largest. Today, even larger projects are operational on the continent—such as Bramley BESS (331 MWh) and Blackhillock in Scotland (400 MWh, with a target of 600 MWh). The company has also developed projects in Poland, including a 200 MW/400 MWh storage facility sold in 2025 to EDF Renewables Polska.
Market Outlook
Although Cheviré is currently the largest operational energy storage system in France, it will soon be surpassed by TagEnergy’s investment in Cernay-lès-Reims (Marne). This project, with an impressive capacity of 240 MW/480 MWh, is scheduled to connect to RTE’s grid at the end of 2025. That’s nearly five times the capacity of Cheviré. Developed in partnership with Tesla, the TagEnergy BESS will aim to stabilize the grid and secure energy supply during peak demand periods.