Would be nice if we started with the actual marginal land and not the marginal land in real estate terms. Roofs for a start. Parking lots next. Really no reason why any and all industrial land shouldn't look like a pure sea of solar from orbit. Every square inch is low hanging fruit no one would complain about a solar panel going in there.
But it's literally not low, it's up on a roof. The ground installs are preferable because they are low and easily accessible.
They still do rooftop solar like I say, it is just at a scale that seems to only pay for the lights in the building and not generate surplus. So a guy still has to be up there no matter what every now and then even right now.
The best land for solar farms tends to be in the desert where there isn’t enough water for industrial use.
But we already have land set aside for industrial use, why not make use of it? Desert isn't free land either. There is a whole ecology there.
Desert ecologies are often boosted by solar (turns out animals spend lots of time in the shade so they aren’t roasted, and solar panels are shade). Industrial areas, at least where I live, tend to be pretty dynamic with respect to structures, I guess you could do it, but you would have to redo it a lot.
Manatees like when you leave a freshwater hose leaking into the saltwater. Ecologist tell you it is bad though because the animal develops a dependency towards human intervention that might not be a long term phenomenon.
Where I live the industrial areas are pretty much two elevations across the entire lot. You get the warehouse where it is a massive building with a flat roof of a single height. And you get where the trucks pull in and back into the warehouse, also a bunch of flat cement with fixed height requirements one could trivially deck with solar.
And when I looked at industrial areas in denmark, or at least in the vicinity of copenhagen, I saw pretty much exclusively that outside actual oil refineries. Just a ton of warehouses, flat roofs, truck yards. Again already with some solar, just only implemented to the extent to supplement a buildings utility bills, using only a small fraction of that massive flat roof, not to produce an excess of energy. I dare say most industrial property the world over looks more or less like that: rectangular building, flat roof, truck yard.