[Christ]

Originally Posted by Daox

Back when I built the panel, I had it sitting in my living room on a cloudy day and it was generating over 12V. I don't think its being filtered. I'm thinking there is perhaps some tabbing material shorting across some of the cells. I cleaned some of the excess up, but left some too thinking it probably wouldn't hurt anything. All the jostling around in the car may have moved the tabbing and is causing current to bypass some cells.

Also possible. I only suggest filtering because your car's windows are designed with a layer of plastic between two layers of tempered glass, and are at a fairly odd angle.

However, your idea sounds more likely to create that much of a drop.