Published: 1 Feb 2021, 13:00 By: Andy Colthorpe The project in Dunkirk, France, with the three or four transformer "building blocks" connected to the PCS units, surrounded by battery storage containers. Image: Total / Omexom. The biggest battery energy storage system (BESS) in mainland France went into operation in late January, and will provide grid-balancing services to national transmission system operator RTE. France-headquartered multinational energy company Total was contracted by RTE for the project, which has 25MWac rated output and 25MWh of storage capacity. It has been built at the site of a former oil refinery operated and owned by Total in Dunkirk, in northern France.