At the French port of Dunkirk, a mothballed oil refinery represents both the legacy and the future of the energy giant TotalEnergies.

The French company shut down the refinery in 2010. Rather than abandon the site, the company is finding new uses for it.

Earlier in the decade, it installed more than two dozen industrial-scale batteries on a strip alongside the rusting tanks and pipes. Some longstanding refinery employees now make the rounds at the battery farm, making sure the devices are functioning properly.

The batteries, housed in white, rectangular containers, are connected to the power grid. They kick in with almost instant bursts of electricity when needed, such as when a nearby aluminum plant, a huge consumer of power, fires up.

Every time a large industrial company starts a machine, “the grid goes down, so you need more power on it,” Damien Grosseau, the head of development and projects at the site, said in an interview at its 1970s-style Dunkirk offices.