A vehicle-mounted generator is powered by relative wind produced by the combination of ambient wind and motion of the vehicle, or by movement of water when mounted on the hull of a water-borne vehicle. A rigid cylindrical housing forms an enclosed interior chamber. Wind asymmetrically enters the chamber through an inlet located on one side of a central longitudinal drive shaft, and exits through an outlet located at the top of the housing. A spiraling parabolic deck forms a floor of the interior chamber, and spirals around the central longitudinal shaft from the bottom of the housing to the outlet at the top. A turbine mounted on the drive shaft within the outlet converts energy of the exiting wind to mechanical energy. An electrical generator converts the mechanical energy into electrical energy for recharging a battery or powering an electric motor.