I'm really torn with this LauraNorder. It has set MrM and myself talking about it. He's lived off grid here in Cornwall for nearly 40 years.
My answer would be yes - roofs where possible but there are constrictions about where solar panels can go.
We are surrounded by woodland (ours). Our panels are ground mounted and sited by the power house (batteries) for one reason. The panels must face south and our little cottage/workplace doesn't have a south facing roof. We are now building a home here for our old age (we're both in our 70s). The cottage is something like out of Poldark! We both see renewables as the way forward so our build faces south and will harness the sun's thermal qualities in a variety of ways. If we didn't already have our PV, the panels would be on the roof but they will stay on the ground. Instead, we are using the roof for solar thermal panels and glazing. My wish is that all new houses had both - photovoltaic and thermal panels - on their south facing roofs. I still see new houses going up not having a south roof. Planners should insist on this.
Thinking of large scale use of solar panels as in the question, they need to be at an angle and if mounted high above the ground, protection will be needed all around them. The struts would need good anchorage or weighting because the gale force winds, we now get, would lift the panels and perhaps even the struts. Same applies with putting them on roofs. It is done, but they can't lie flat and have to be part of the structure of the building (rock solid anchorage). Many of the buildings mentioned have flat roofs. We've all seen the damaged caused by the winds over the past few winters.
To put them onto factories, barns and schools would be at the expense of the owners of these buildings. The power produced benefits that building first and then any left over can be fed back into grid and the owners are paid for this.
It is totally different when looking at the installation of a solar farm. We have one close to us. In this instance the land was not suitable for agriculture. The farmer leases the land to a solar company, who built the solar farm around the few existing trees, which are very short, and nothing on the land was disturbed.
Planners here in Cornwall do turn down applications for solar farms. One quite recently. Objections all related to loss of agriculture land and it's an AONB. Farmers and landowners don't sell their land to the solar companies, the lease it and can make more from leasing their land than farming it.
However, Cornwall could be getting two more solar farms which will be a total size of 150 football pitches. The amount of power generated will feed 24,000 existing homes and any surplus will be fed back into the national grid. I believe one of these is on land totally unsuitable for agriculture or growing trees. It's in our Clay Pit area. The amount of waste from mining in Cornwall has had a huge effect on usable land for agriculture. Some of the land has been put to good use: Eden Project. It's very common place for Phase 1 and 2 mining surveys to be done for Planning Permission.
40% of Cornwall's energy is produced by renewables and it's growing. I hope sources of renewable energy will continue to grow to help with the reduction of carbon emissions.
Much of what I write has come from MrM. All questions will be forwarded to him ?.