“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
Day or night? As a kid we used to heat with wood - every morning I'd wake up and start the first and then take my shower... The fire was out by 9am, but the house was noticeably warmer at 12 than 9am anyway from solar, and we didn't need to light the night fire until 7-8pm (the sun went down around 4pm), and it would burn on low all night.
The coldest days tend to also be clear skies. Cloudy days did not get nearly as much solar heat, they needed less, but we would have to light a fire again at noon to get through the day.
Which is to say you can get more than enough solar to save your life if there is a reasonable amount of insulation in the car if it is daytime - but it wouldn't be enough to get through the night when you need the heat most.