If it's about using wasted land, why not put them beside the rails, which would make access easier? There is usually a generous margin beside the tracks.
This would also allow bigger panels to be used.
And the RightOfWay is already maintained to keep thin grasses & trees away that may fall on a line.
Often the line is already built-up for flood prevention.
In some (most? All?) countries, the railway has free reign and doesn’t need to answer to city/municipal/states/provinces for approvals on anything.
A main “downside” is the poor production in winter/mornings/evenings on ground-parallel panels. e.g. France has huge solar capacity, they tend to be heavy electricity exporters in summer and heavy importers in winter. One of their new tariffs offers discounts except for 22 days in winter.
https://www.rte-france.com/en/data-publications/eco2mix/powe...
0 degree panels produce the most when electricity is valued the least.
Output should be measured in currency, not MWh.
augur cars overturn the soil and lay pipe but now the fiber optic lines would compete with the solar.
meanwhile track lines are untapped, and often use electricity or having wiring for local induction loop