No, it would work, but as time wore on and the cars (Which we all know go through some rough weather) went places, it would get less and less efficient due to use. For the first week it would be great. ;D
The only other alternative I can think of is using this stuff that my dad uses on the car every now and again, when we go on long road-trips to protect the windshields. We could use that on the solar panels. Hydrophobic glass polish, or something like that.
Other than that, it would just require some simple, extra maintenance to keep it clean. Personally, if I don't have to use gas, or I have to clean my car more instead of going to the gas station, I'm cool with it. Haha.
Perhaps even make it that much simpler and allow them to be removable to clean.
My only concern then is after a crash or accident. You'd have to spend thousands to get new solar panels. Doesn't sound appealing.