Grid-scale

France’s largest battery storage system powers up

The 100 MW/200 MWh battery energy storage system (BESS) is connected to the grid with a charge and discharge voltage of 63 kV. It is expected to be fully operational by the end of 2025.

By

Marie Beyer

Aug 22, 2025

UK-based renewables developer Harmony Energy recently switched on its battery energy storage system (BESS) at the port of Nantes-Saint-Nazaire. With 100 MW of power outut and 200 MWh of storage capacity, the facility is the largest of its kind in France.

The project is connected to the Réseau de Transport d’Électricité (RTE) transmission network with a chare and discharge voltage of 63 kV, which is considered an ideal configuration for the grid balancing services for which it is intended. The BESS is equipped with Tesla Megapack batteries and the Autobidder control system to manage charging and discharging in a smooth and optimized manner.

“The operational lifespan is expected to be around fifteen years, but it can be extended by upgrading the equipment,” a Harmony spokesperson told pv magazine France , adding that the project should be fully operational by the end of 2025.

The project is located on a site previously occupied by the Cheviré power station, which was operational from 1954 to 1986 and fuelled by coal, gas and oil.

“Energy storage is much more than a technical link in the energy system: it is a fundamental pillar for building a new low-carbon, reliable, competitive and more sustainable model. The Cheviré storage park is an emblematic achievement for the energy transition in France. It illustrates how we can convert former industrial sites into assets for the future, serving the electrification of our energies,” said Andy Symonds, CEO France of Harmony Energy.

From pv magazine France

Written by

Marie Beyer

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