Talking about solar cells on a roof to generate power.. Blackfriars rail station in London was refurbished to have entrances either side of the river Thames.
The new roof is covered in solar cells. The power they generate powers the lights for the station. All well and good of course.
But 100 ton trains need a good deal more power than that. I would expect the same thing for data centres. You might be able to power the lights and staff areas, but not racks of servers using roof mounted solar cells.