Electric Vehicles

This is a very common idea when it comes to EVs, and the conclusion we've come to time and again is that the juice isn't worth the squeeze. Even overcoming technical hurdles like how to actually get the power from your panels to the batteries, and installing the panels into the van so it is still aerodynamic, you still have the problem that you simply need more panels in order to get a non-negligible amount of charge in a reasonable period of time. Your calculations are assuming the panels produce 800W of power all the time - but that is the maximum amount they can produce. As soon as anything changes to make power generation less than ideal - change in sun angle, dust accumulation, clouds, etc - you lose power from your calculation. And for the amount of time and money you would spend on this project, your break-even point on electricity cost savings would likely be infinite.

For reference, this is what a solar car designed for the purpose of running off its own electricity looks like:

https://en.wikipedia.org/wiki/Tokai_Challenger

The solution is to simply charge the car from your home solar array. Hopefully your utility/government pays you or gives you credits for excess power you generate, so you can generate during the day when you drive and charge at night. Or you could get a home battery bank. If you don't want to do a full home solar install, you could build a car port out of 2x4s and mount a few panels on top of that as a DIY project.