[oldtamiyaphile]

These are older tech panels with aluminium backing, they only bend in one direction. They also transfer a LOT of heat to the paint, steel and onto the car interior (depending on insulation). This may ruin nice shiney paint in time.

At best, you're likely to see 2A from one of these panels in full summer midday sun (depending on your latitude). The effect is about the same as switching the radio off.

Mounted on a car roof these panels get very hot and their efficiency drops, they really need and airgap to keep them cool. I currently have a 100mm (4") airgap under my panel and a heatsink setup underneath to keep the panel cooler. With the original 10-12mm air gap I found the underside of the roof got unacceptably hot, and running that A/C to compensate won't exactly help economy.

Can I see any gains from the panel? Not remotely. It does let me EOC knowing that as soon as I park it, the battery will be recharged to full within 15mins on a sunny day or half an hour or so when it's cloudy. I have one of the newer plastic backed panels that claims 22% efficiency, and an MPPT controller.