Here is some long term experience in Scottsdale AZ:
1995: Installed a PV system with 40 ea 75W Siemens (ex Arco Solar) modules (3000W) with two Trace SW4024 inverters with batteries, but utility connected.
2007 New owner, poor performance of the system. Inverters and modules out of warranty. Two problems: Inverter setpoints drifting such that one inverter was selling to the utility because battery was full charge voltage, other inverter was charging the battery, even from the utility at night. Adjusted setpoints, but same problem developed. Owner decided to replace the two inverters with one SW3000 and of course no battery. In rewiring the array to 20 series modules and checking the modules, found that about half of the modules were degraded to about 50% of initial power. No similar size modules available, so repositioned to make two strings of modules, one "good", one "poor". Noted that the "poor" modules were much darker backskin.
2017: Addition to the residence. Essentially no output out of the "poor" string that was in parallel with the "good" string on the single input inverter. Installed 16 ea 300W PV modules (4800W) in the original area and 7200W on the addition. Old PV modules were donated to the PV testing lab at Arizona State University as they were interested in the differences between "good" and "poor" modules.