Fingerprints on Solar Panels with Anti-Reflective Coatings (ARC)

[miracj]

I am currently in the installation process of Sunpower 345 W AC panels (micro-inverters built on the back Model SPR-X21-345-C-AC).

I was told that they have an Anti-Reflective Coatings (ARC) on the panels and thus should not be handled without gloves. Well the workmen from the solar installation company (a Sunpower elite dealer) got fingerprints all over them, and didn't use gloves (at least not initially).

Attached is a photo showing some of the panels with fingerprints (visible as light blue streaks on black sections, download file to see it in more detail), which is typical across many of the panels (possibly not all of them, but I need to examine them all carefully under the right lighting).

SolarPanelFingerprints.JPG

I have several questions.
1. Has anyone experienced similar installation issues?
2. How much do the fingerprints, affect the power output?
3. Can the fingerprints be cleaned off with out ruining the ARC, and if so, how?

Thanks!

[Mike90250]

2. How much do the fingerprints, affect the power output?
3. Can the fingerprints be cleaned off with out ruining the ARC, and if so, how?

Going to have to ask the Mfg as to the consequences. But with the prints, at least you know who to bill for the replacements.

FWIW - when I get new eyeglasses, I NEVER order any of the 6 flavors of "coatings" that you can get. They all show dirt and prints horribly and unless you keep them spotlessly clean, they look awful.

If I was in a communications free zone, I'd try regular window washing mix of water & ammonia 10:1 that cuts most grease. 2nd pass, I'd double the ammonia up to 20% Beyond that, you are looking at serious corrosion issues. Next try would be water & alcohol , no more than 20%
And wash in the cool of the day, don't shock the hot glass with cold water!

[miracj]

Going to have to ask the Mfg as to the consequences. But with the prints, at least you know who to bill for the replacements.

I spoke with Sunpower tech support today, and their response said that it does not affect solar production, and that rain was enough to keep them clean.

Of course, no rinsing with a hose or water when the panels are hot, but only after they have cooled off (early morning, late evening, cloudy day, etc). Based on google searches of cleaning eyeglasses with Anti-reflective coatings, they basically say collectively (for eyeglasses, not solar panels), and for what it's worth (and I'd love to find a more authoritative references though) to

1. Rinse as much dirt off 1st with water
2. Only clean when wet. Use either water, or water with a small amount of regular kitchen dish soap (no additives like citrius). Do not use ammonia, alcohol, Windex or any other liquids as a wetting agent.
3. Use a microfiber cloth (made of cotton or similar - never wood pulp like tissue paper) to clean with a light touch and only while it is not cleaning a dry surface. Keep cleaning surface of cloth clean, and rotate to clean area when soiled.

I'm still a bit uncomfortable with Sunpower's answer, but will go with it for now. I will see if the fingerprints change or disappear over time and report back after many rains or in the spring.

Thanks again!

[emartin00]

Finger prints aren't going to do any damage. To remove them, just use a damp cloth.

[cebury]

Expect to get much worse on them, like bird poop. My filthy panels, which were so dirty it was reducing production 20-30%, we're spotless after the first hard rain.

[miracj]

Expect to get much worse on them, like bird poop. My filthy panels, which were so dirty it was reducing production 20-30%, we're spotless after the first hard rain.

I'm kind of surprised that bird poop gets cleaned off. I have bird poop on my cars occasionally, that never seems to come off no matter how hard, or how long it rains unless you scrub them.

Have you inspected the panels close up or are you just looking at it from the ground?

Also, how do you determine your production changes by 20-30%? I can only see comparing days close to each other (so angle of sun is similar and trees with similar foliage) with cloudless days (so they do not factor in) with a before and after cleaning as a valid methodology.

Thanks!

[cebury]

I'm kind of surprised that bird poop gets cleaned off. I have bird poop on my cars occasionally, that never seems to come off no matter how hard, or how long it rains unless you scrub them.

Have you inspected the panels close up or are you just looking at it from the ground?

Also, how do you determine your production changes by 20-30%? I can only see comparing days close to each other (so angle of sun is similar and trees with similar foliage) with cloudless days (so they do not factor in) with a before and after cleaning as a valid methodology.

Thanks!

I've only had one pile of poop on mine in last 12 months and it's completely gone now.... from the roof view. That only proves that one bird's poop on that one day, it's obviously anecdotal so take it how you want.

I have 28 panels and let them get filthy and have solaredge monitoring. rinsed off half of them, didn't even scrub them, and the average between the dirty half was about 25% less than the clean half. the averages before hand were the same for each half since there was no shade. just an average and not scientific, but I can tell you for sure that before I did this test, when they were filthy, then one got replaced in the center, that one produced 30% more than the ones next to it everyday until i washed them. there was certainly a nondegradation + different at batch manuf tactors in there since it was new against the other 7 month old panels. But drop a couple % off 30 and back to 28% ish.

I was surprised it was that much since I was skeptical about those % claims made by solar companies charging for washing. But we got almost zero rain here 9 months, sometimes 10 months during drought.

[J.P.M.]

I've only had one pile of poop on mine in last 12 months and it's completely gone now.... from the roof view. That only proves that one bird's poop on that one day, it's obviously anecdotal so take it how you want.

I have 28 panels and let them get filthy and have solaredge monitoring. rinsed off half of them, didn't even scrub them, and the average between the dirty half was about 25% less than the clean half. the averages before hand were the same for each half since there was no shade. just an average and not scientific, but I can tell you for sure that before I did this test, when they were filthy, then one got replaced in the center, that one produced 30% more than the ones next to it everyday until i washed them. there was certainly a nondegradation + different at batch manuf tactors in there since it was new against the other 7 month old panels. But drop a couple % off 30 and back to 28% ish.

I was surprised it was that much since I was skeptical about those % claims made by solar companies charging for washing. But we got almost zero rain here 9 months, sometimes 10 months during drought.

Every location is different. I don't doubt what you write for one hot second, but 25% reduction is quite severe. Without rain, my array seems to foul at the rate of about 1%/week or so, and (going out on a limb here a bit) the performance degradation due to fouling seems to level off at somewhere between 7 - 10 % performance penalty vs. a clean array. That's more sketchy than the rest of my SWAGS on this because I've not had a rainless stretch beyond ~ 10 weeks since I started measuring the effect of fouling on my array. A decent rain restores about 3/4 the lost performance due to fouling.

As for cleaning/hosing, I've found that simple hosing in the A.M. before the P.O.A. irradiance gets much beyond ~ 100-150 W/m^2 seems to remove ~ 80-90% or more of the accumulated dirt and restore most all of the clean performance. FWIW, I've found 2 go rounds, top to bottom using a total of about 4-5 gal. of water per panel seems to get as much improvement as 10 gal./panel. 1-2 gal./panel just gets things wet and tends to cake the dust a bit for little improvement. A

Another result I've found is that water spots on a clean array do not affect performance. That is, I cannot detect a difference in performance between a clean array with wather spots and a clean array without water spots.

[cebury]

Yeah and every location is different. I'm sandwiched between very large trees in each side of me. they don't shade but do spread tons of fine pollen, combined with heavy construction a few doors down and yuk.

2016-09-14 13.56.50.jpg

here is the pic before I sprayed both sides.

[cebury]

I could get all my details together with graphic images of each side, before and after, and averages, etc. Been meaning to, haven't yet.

[SunEagle]

Yeah and every location is different. I'm sandwiched between very large trees in each side of me. they don't shade but do spread tons of fine pollen, combined with heavy construction a few doors down and yuk.

[ATTACH=CONFIG]n337981[/ATTACH]

here is the pic before I sprayed both sides.

I would say that the pollen on your panels is a little more concealing then normal dirt that collects on solar pv. It almost looks like someone spray painted them so I can believe a major increase of production just by cleaning them.

[miracj]

I have 28 panels and let them get filthy and have solaredge monitoring. rinsed off half of them, didn't even scrub them, and the average between the dirty half was about 25% less than the clean half. the averages before hand were the same for each half since there was no shade. just an average and not scientific, but I can tell you for sure that before I did this test, when they were filthy, then one got replaced in the center, that one produced 30% more than the ones next to it everyday until i washed them. there was certainly a nondegradation + different at batch manuf tactors in there since it was new against the other 7 month old panels. But drop a couple % off 30 and back to 28% ish.

With individual panel monitoring of solaredge, or micro-inverters systems (which I have), that makes perfect sense and is a good methodology. Depending on how you clean them, I can see washing every alternate ones (perhaps in vertical stripes) might return a better comparison if there might be shading on the panels.

If one had string inverters, washing one string vs another string (depending upon their location and similarity) might also allow power comparison.

But cleaning requirement also seems to be dependent upon location (dusty, bird population, tree pollen, etc) versus rain & wind frequency (maybe snow too, as it might pull the dirt off better than liquid water)

Also, do birds ever sit in the middle of a panel, or just the edges of an array? Are bird spikes needed or useful?

[J.P.M.]

Yeah and every location is different. I'm sandwiched between very large trees in each side of me. they don't shade but do spread tons of fine pollen, combined with heavy construction a few doors down and yuk.

[ATTACH=CONFIG]n337981[/ATTACH]

here is the pic before I sprayed both sides.

Understood. I'd hose it ~ 1X/month or as needed. Goes that swamp cooler off to the west cast much shade ?

[DanKegel]

I agree with Mike that antireflective coatings on glasses aren't worth it - the coatings just bother me. (But then I'm the kind of guy that prefers cars with hand crank windows and no radio... getting hard to find 'em these days )

[SunEagle]

I agree with Mike that antireflective coatings on glasses aren't worth it - the coatings just bother me. (But then I'm the kind of guy that prefers cars with hand crank windows and no radio... getting hard to find 'em these days )

Have you tried looking in Cuba. I believe a lot of the older US cars went down there.