[RedDevil]

I have a small solar panel on the inside of the trunk window of my Insight; it is hidden from view (from the rear view mirror) by the roof beam between the C pillars so it is not in the way.

The purpose is to keep the 12V battery charged up while parked. The Insight has a not insignificant draw and would deplete the 12V battery in a couple of weeks otherwise; it killed my first battery within the warranty and its replacement wasn't very good so to avoid further trouble I added the panel.

It should help with economy too (a tiny bit) as the car has to charge the battery less while driving as it is almost always near full - especially in these COVID times with long pauses between drives and mostly short errands.

The panel can get fairly hot in the sun, but the light would hit the interior anyway so I guess it has little effect on the overall temperature inside.

I believe it is useful. I'm pretty sure it helped extend the life of my 2nd 12V battery by a couple of years.