Looking at that roof, it looks like it's about 3m x 1.5m, for 4.5 m^2. Typical solar panel gets about 200W/m^2 at max sunlight.
So that's a peak generation of 900W. With a 24 hour day and a capacity factor of 10%, that's about 2.16 kWh of energy per day. For a van like that, with the weight and aerodynamics of a bulky solar system on the roof and the systems for storing that energy in another battery and cleanly providing that power in a way that the car charging system can accept? I'd be skeptical that's good for more than 8km per day, on a sunny day.