alt Hacker NewsThis might be exactly what you are asking for: low cost and low hanging fruit.
On paper, this should be pretty cheap. Normally, you need some mounting infrastructure to put the panels on, land preparation, etc. In this case, the train track provides the supporting infrastructure. You can bring in the panels via train wagons. Installation should be pretty quick and straightforward. And for cleaning, you could just do that from a rail wagon as well. Not having to truck in anything seems like it should be a big bonus here.
Durability might actually be fine. Solar panels are pretty reliable. And it's not like the train is in direct contact with the panels. The vibrations might be a challenge but presumably that would have shown up in the trials. It's something you could engineer solutions for. And so what if a small amount of panels fail?
Another issue with solar deployment is that there needs to be power cables that can consume the electricity.
But a train company practically always has running trains when the sun is shining. So they wouldn’t need to worry about disabling and losing money on the panels.
The real challenge is economically connecting the panels to a rail substation.