I just use them on my sailboat. Mine are close to ten years old. I use a Link 20 monitoring system. I can see the rate they charge my batteries and in optimal light conditions they still produce more than 90% of what they did when new in optimal light conditions .
Regards
There is no mystery here.
I watched a 35kw bank installed 10 years ago.
I attached the Internet based telemetry system to them.
Never put out more than 5kw on the brightest summer day.
If they worked they would be in wide - spread use.
Mine are out rain and snow, from 80-100 F in the summer to -45f in the winter. They take a beating from the elements 365 days a year.
That’s why they don’t last very long. Nothing does.