“The solar cells provide us with more than 50% of our needs,” says Boubaker Siala, founder and CEO of Bako Motors. “For example, the B-Van, for commercial use, you can have free energy for about 50 kilometers (31 miles) per day… 17,000 kilometers (10,563 miles) per year. …….. The B-Van, which can carry 400 kilograms (882 pounds) of cargo and has a 100 to 300-kilometer (62 to 186 mile) range, is designed for logistics and last-mile delivery, with prices starting at 24,990 Tunisian dinar ($8,500)."
It varies widely by vehicle type, etc - but travelling 31 miles costs you in the ballpark of $3 in the US or €5 in Europe. So that's around $1,000/€1,800 of free fuel every year if you were using this vehicle most days. The B-Van is small, but perfect for local deliveries, especially if paired with swappable batteries.
You know what will never pay for itself with its self-generation fuel capacity? A gasoline combustion-engine car. Here's another pointer, they're rapidly becoming the transport option of yesteryear.
The solar-powered compact car driving Tunisia’s electric vehicle revolution
The energy provided by a car-roof-sized solar panel would be completely, totally negligible compared to how much is used by a typical electric car. The only reason it works here is because these cars are so tiny. For a standard 4-door model? It would be a waste of time, and better to just put that panel on a roof somewhere instead.