Even when they are not exposed to any light and not producing power, solar panels will glow and move as if they were. I think when they're not producing power they should just looked like they do when they're disabled or have no wire connected to them like the one on the left in this image:
Steps to Reproduce
Build a solar panel in an area where it does not receive any light and connect it to a wire
This issue has not been confirmed by a developer yet.