Why not larger solar panels above the electricity lines? I've seen some rather heavy-looking metal bars for holding up the electricity lines, maybe they could also support some panels, with minimal extra material use for mounting. Up there they would provide some shade (which should be good for the grass if there is any between the tracks, given that way too dry + hot summers are becoming the norm), and require much less cleaning to stay efficient.

Unlike solar roadways, this actually makes sense. Lots of tram systems also use DC, eliminating the need for inverters. And yes, panels are so cheap it's not too bad that they're horizontal; vandalism is a greater issue.