Hear me out put them on the cars, it can be a little rough up there as well but no where near as hazardous to the panels as in between the things like auto carriers tanks and a variety of hoppers you get like 200sqft per car just on the top empty a car is 30-40 ton so adding another 2% for panels and energy storage isn’t a big deal the extra operating cost to the train is minimal on flats trains run like 1.0-1.6 HPT (horsepower per ton) to maintain 60 mph, the engines are already diesel electric just spend the payout through the engine and the added wind will help keep the panels free of debris.

I reckon you could top and side the cars and guarantee solar production from top and one side at a time 100 cars on a double set train x400sq ft top and one side =40,000 sq feet of solar panel x 20 watts =800,000 watts / 750 watts per hp it’s a bonus 1000+hp in the sunlight pretty good considering 100loaded cars can be pulled by 8800hp.