Could something be wrong ? Some year over year comparisons

[rhedayi]

I check my solar output daily......I had my panels installed last year. 16 sunpower 327s with a SMA6000 inverter. The daily outputs last year were higher than this year. I know the panels degrade at 0.5% but the difference seems more like 5%. I washed the panels a month ago so they are clean (cleaner than the same time frame last year as they were not washed)
Here are some numbers...I chose days that were sunny without drop off through the day. Could this be normal output variation based on weather etc ? Almost seems like one panel may not be performing..... I called my dealer they came and said the voltages were fine (tested in the inverter). Then I called sunpower and they said, you are performing about the estimated amount for the months so it is fine. Is there a better way to check on this ? I recall a different website for SP monitoring, but dont recall details or if it would be more helpful.

[sensij]

5% from one year to the next doesn't sound like much. Have you accounted for differences in temperature, wind, and air quality? If it has been a month since washing, a few percent could be coming from soiling, and the first year degradation will typically be higher than the 0.5% you might expect later (even for Sunpower).

[rhedayi]

I have not checked the temperature, humidity etc. I think the daily temps are similar but who knows. Panels were never washed since this year so they were dirty the whole time last year.