But 24 km per day is under ideal conditions (perfectly sunny day, mid-latitude, panels angled southward) and 500W requires 2 square meters of panels[1].

Unless you own a big American pickup truck, it's hard to see where those panels fit on the car. And if you do own a big American pickup truck, you will not achieve the 150 Wh/km assumed by the GP (it will be more like double that). GP also used quite optimistic loss figures for conversion.

It begs the question: Why not a Nissan Leaf and solar panels on your (home) roof?

[1] Only 1000 W of solar energy falls on each square meter of the earth's surface at noon. The best commercially available solar panels have about 25% efficiency converting light to low voltage DC. This means you need a flat surface of about 2 square meters directly facing the sun to collect 2000 W of light, which will achieve 500 W of electrical power.