A row of tall white boxes by the side of a Sierra foothills highway could represent a key piece of California’s future electric grid. Made by Tesla, the boxes contain thousands of battery cells — the same cells that power Tesla’s luxury cars. But at this installation, at a Pacific Gas and Electric Co. substation in Browns Valley (Yuba County), the batteries soak up electricity whenever it’s cheap and feed it back onto the grid when demand hits its daily peak.

The project, operational since the start of the month, represents a collaboration between PG&E and Tesla on one of California’s biggest energy goals: storage.

SFGATE