Also, you usually crush and shred the materials in solar panels for recycling, so no one cares if replacing a panel means smashing it to quickly get it out between the tracks. Train tracks move far more than most people would expect, so the panels are already going to have a built-in buffer zone in which you can quickly and easily place a panel. As someone else said, something riding on the rails would likely be leveraged for installation.

Rails have a fairly consistent width when measured on a rough scale, as does the vehicle riding the rails have a fairly consistent center point. As long as the electrical leads are robust enough, and the contacts forgiving enough towards slop, the panels could be designed to just drop in. If curves are too difficult or expensive to accommodate, only install at the flats.

As with any program like this, as long as the overall energy output exceeds the cost of installation, then it's totally a net positive, even at the lowest levels of efficiency. And if parts break, but you're still netting positive, then little or no maintenance should be considered over the lifetime of each hardware deployment.

The key thing is ensuring that contracts with suppliers and workers are reasonable and benefit local communities. But that's just about the biggest difficulty with any transaction these days, isn't it?