HALLERED, Sweden — The plume of white smoke from Volvo’s fuel cell truck matched the white clouds in the Scandinavian sky. Stand too close and you feel the descending mist of water vapor.
The hydrogen tanks sweat just droplets at first. Then comes the release of about a liter of water, approximately the amount the 100-kilowatt fuel cell produces per kilometer traveled.
On a spin around the track at Volvo’s high-security proving ground about an hour east of its Gothenburg headquarters in southern...