Okay, finally some valid points.

The problem is that it's just better to put the panels some meters on the side, or better yet, elsewhere. Electronics and solar panels just don't like the vibrations from 1000 tonne trains making them vibrate all day long.

I also think you wildly underestimate the simplicity to have some sort of automatic, or semi automatic "train" installing those panels. Removing the bad ones etc.

It all boils down to, is it economically viable?

It just adds costs, the cost of setup, the cost of running it, also it will most probably not function as many years, when they are dirty they will produce less. So only more expensive.

Also, how are you going to transport the electricity along hundred of kilometers of panels laid out as a string? Low voltage is secure but lossy. Have power stations that inject it in the 20.000 volt lives overhead? More costs.

If we lived on a very small planet filled with trains, maybe Solar Trainways TM would have a chance, here on planet earth, not so much.