[jacquesm]

I think you should factor the savings on AC in the summer and heating in winter as well into your calculation. For that to be most efficient the air would need to be trapped behind the panel, I don't think you need to worry about overheating so much because they are going to be running at a low fraction of their theoretical capacity. There is a fair chance that including savings on heating and cooling it will actually work out but I haven't run the numbers in detail. But it certainly is an intriguing proposition, even if it would work only on South facing walls.

[Phenomenit]

We don’t have AC installed so our only major energy cost during the summer is hot water . Yeah it’s definitely worth doing som maths. One major pain point though is that we need a permit for vertical panels because it affects the look of the house.

[jacquesm]

> we need a permit for vertical panels because it affects the look of the house

That's fairly common, but usually only on the front of the house. And on extra buildings like a garage or a garden shed such restrictions may not apply. This is pretty trick and it varies enough from one place to another (even within the same country, province or state) that it is worth researching before embarking on such a project.