No Cleaning - Installed Nine Years

[sabersix]

I'm in San Diego, CA. I recently had my roof replaced (lift and lay). I hired my original installer to remove and replace the solar panels which had been installed since 2015. I have never cleaned them. This is how they looked. I cleaned them before they went back on the house. I'm seeing a small bump, but not a lot.

Daily Data Picture.jpg

Full panel.jpg Panel Close Up.jpg Panel Close Close up.jpg

[J.P.M.]

Without more information it's hard to judge what type of improvement to expect from cleaning, especially over short periods of a month or two and with no information about the variables that control array efficiency and output, especially irradiance.
I'm in 92026 and as best as I can educated guess or estimate, my array's fouling penalty from not being cleaned seems to level off (become asymptotic) at somewhere around a 10 - 12% fouling penalty below clean performance.
Also, as best as I can calculate, my average annual performance decrement has been a bit less than the spec sheet figure of 0.40%/yr. relative to STC performance (~ 0.35 - 0.40%/yr).
The system has been active since 10/13/2013 and not missed a beat.

[nomadh]

I cleaned mine once and saw very little difference after cleaning

[J.P.M.]

I cleaned mine once and saw very little difference after cleaning

If you live in an area that gets a reasonable and/or regular amount of precipitation, you may not see much effect from cleaning simply because the array doesn't get that dirty.
There are other reasons as well.
Besides, one cleaning is not necessarily a good determiner of cleanliness.

[MGE]

Yeah I try to clean mine every month as I live in San Diego about a mile inland from the coast (Clairemont).
For me it does seem to make a difference in production, about 10% as JPM stated.
A couple of times I have cleaned only one of two panels that are side by side and get for the most part the same Sun exposure and conditions and the cleaned panel always outperformed the uncleared panel.
Access to my roof couldn’t be easier as all I have to do is go out on our upstairs balcony and step off.
My system went online back in May of 2013 and has been 100% trouble free.
Knock on wood.