European electricity companies and Japanese carmakers are working to develop services that allow power stored in electric vehicle batteries to be sold back to the grid.

E.ON, EDF and Nissan are now trying to persuade European carmakers to follow suit, Reuters reads.

With millions of electric cars expected on European roads over the next decade, utility firms see both an opportunity to sell drivers more electricity and a risk that surges in charging at peak times could destabilize stressed power grids.

That’s why E.ON is working with Nissan to develop so-called vehicle-to-grid (V2G) services, including software for aggregating and marketing charging data so the German power company can predict peaks and troughs in electricity demand.

Nissan’s idea is that if you charge your electric vehicle (EV) at off-peak times and are prepared to sell power back to the grid when it’s under strain, you could effectively charge for free.

French utility EDF has teamed up with San Diego-based V2G technology specialist Nuvve to build the first commercial-scale V2G charging network in Europe for vehicles made by Japan’s Nissan and Mitsubishi.