Interesting analysis, Louis!
As I live on the first floor, the possibility of installing a vertical panel in one of the windows is still something that doesn't appeal to me very much, because as my monthly electricity consumption is under 50 euros, the savings would have to be considerable for the initial investment.
Your post has aroused my curiosity, and maybe one of these days I'll stop by one of the electricity distribution companies to get a simulation of the initial cost.
It's always good to see investments that pay for themselves and end up being a profit after a few years.