Comment by mixermachine

It exists and does degrade panels but the time horizon is pretty wide. Real world data shows something like 0.5% to 0.7% degregation per year on average. At the start the degregation is higher and but it slows down with age.

So a 20 year old panel might be at around 80% in the worst case. Often they are in much better shape. This seems like a pretty good deal to me.