The challenges are what makes them impractical. The company has investment it needs to repay, so it obviously wants to tell you it's not a big deal. It's much more cost efficient and solar efficient to install them on roofs of homes and building, create shelters from them, or simply just make a field of them. Things like "solar railways" should be a last resort, after we have already covered the obvious solutions.

the panels are protected by the rails,

Think a little harder.

Yeah by a long shot. Railroads spend 1-3% of the capital cost on maintenance. So if it cost $3 million to build a km of track they spend roughly $30-90k/year. It might not look like it since tracks are just kind of always "there" but there is a decent amount of work you need to do pretty much constantly.

The stones underneath the tracks and sleepers is called ballast and it needs to be rough, angular rock of a certain size. It's an engineered fill material that's designed to lock together and hold the rails in place. Every train that passes by does a couple of things at once. It cyclically loads the ballast and breaks down those sharp edges that lock it together. At the same time the force of the wheels on the rails contributes to fatigue causing microcracks to form on the rail surface.

If you leave rails unmaintained long enough (by gross tonnage BTW. Rail can last a long time if it's hardly used at all) the track will start pumping, where it compresses and expands as each axle passes over it. You'll start lifting the subsoil up into the ballast ruining its ability to hold the track in alignment even more. Also, microcracks can combine enough that the railhead begins spalling and eventually the cracks can combine enough that the rail itself can fracture well before it's service life tonnage.

To fix this you have to tamp ballast every X number of tons, grind the railhead every Y tons, and replace the ballast every Z tons .etc

Basically every part of the permanent way is some kind of wear item that needs maintenance. Mind you, only mainline track needs to be perfect. As long as speed limits are low enough along with an inspection, you can run on degraded secondary rails or spurs safely. It just wears it out even faster.

An American rail section that last saw maintenance when reagan was elected

or just put panels on flat top buildings and cover parking lots.