Comment by SideburnsOfDoom

The 5-10% number is completely invented. I doubt it's half as high as 5%, but until and unless someone does the maths, there's no point in speculating.

The math has been done many times for solar panels on the roof of cars, and it's not worthwhile. Ships are not the same though.

At any rate, it's inevitably far more sensible to put a larger solar panel + battery installation at a fixed place on land, and charge vehicles from that.