Comment by footydude

> How common is it that these industrial/commercial buildings have roof-top solar? If not common, what stops it?

One factor is weight - a lot of low-cost industrial units may well need modifications to the roof to strengthen them to be able to take the additional weight of solar panels.

Certainly where I work (science research facility in the UK) our business has only been able to install roof-top solar on a comparatively small proportion of our total roof space because a large amount of the seemingly viable space would require substantial works to make the roof strong enough for solar.