[HuntingHawk]

Debris that normally strikes a vehicle that you think little about would seriously damage the solar panels. Even dirt or sand kicked up by wind will degrade the panels.

 

[HuntingHawk]

The panels need to be point towards the direct sunlight. So if they are on top of the car they would only be working at 100% at noon. Suppose you could open or close the hood and trunk every couple hours.

Even then it may not be 100% because of the longitude of the sun changing from month to month.

 

[HuntingHawk]

You miss one important point in your thinking. That is the battery voltage of the car. Seems 96VDC is common. So if you are talking 350 watt panels (assuming 12V panels) you would need 8 in series to get the 96 volts & still only be adding 350 watts maximum.

 

[HuntingHawk]

This maybe alittle off topic, but there is an older couple out where I live that have a 48VDC electric golf cart. They use the cart for checking their mail at the end of the road & such. They have a pair of 240watt 24VDC panels set up for solar charging their cart.