Hopper cars and solar panels

[AmtrakPDX]

On a recent trip, we passed quite a few hopper cars. I noticed that many (most?) had what looked like solar panels, about the size of 3-4 sheets of notebook paper, up high on one corner of the car. It seemed that they were in a very vulnerable location but I was also wondering what they were powering. Any ideas?

 

[PetalumaLoco]

Patent application title: Acoustic monitoring of railcar running gear and railcars

See paragraph 23.

 

[PetalumaLoco]

 

[transit54]

I believe they're actually used to power equipment to determine where ballast needs to be released. See the latter part of the discussion on this thread:

http://www.zealot.com/forum/showthread.php?t=165072