I was in the mountains of North Carolina a few weeks ago. There was a NCHP car sitting in a work zone. It was covered in dust and no one in it. Looks like it had been sitting there for a while. The lightbar was on as is normal, to warn motorists. On the trunk, was a huge solar panel. It covered the whole trunk lid. Was really a strange set up. The lightbar was a strobe bar so I doubt that solar panel was running the bar, but who knows. Im thinking it may be used to supplement the charging of the battery, as the alternator at idle for extended periods of time may not be able to keep up a good charge.