What about vibration? Any issues there? I would worry that if you drove on a long washboard road that wires could start to break. Also could the panel get damaged if you slam the hood too hard when closing it?
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I could see rigging up some kind of a mounting system where as soon as you stop, the panels come out and get attached to the hood - that seems to make sense to me. But I don't think I'd want them there all the time. Potential of damaging the panels (rocks kicked up by other vehicles, hail, etc) and also glare off the panel (flat surface = mucho glare. I know that because I owned a 1990 Montero with a very flat hood! Driving towards the sun was very unpleasant!)