Cleaning solar panels

[littleharbor2]

I bought and removed a system off a house in San Jose that had nearly flat, level panels. I imagine the wanted the system removed because it wasn't working. It included a Trace SW 4048 inverter, two Trace charge controllers, A Trace metal, outdoor rated enclosure that housed all the equipment , Batteries and about 36 solar panels. It was obvious to me why the system had stopped working. Being oriented almost level they were so covered in dirt you couldn't tell they were solar panels.

The inverter is working to this day. The enclosure is housing new batteries and I'm sure the charge controllers are still working as well.

[J.P.M.]

I bought and removed a system off a house in San Jose that had nearly flat, level panels. I imagine the wanted the system removed because it wasn't working. It included a Trace SW 4048 inverter, two Trace charge controllers, A Trace metal, outdoor rated enclosure that housed all the equipment , Batteries and about 36 solar panels. It was obvious to me why the system had stopped working. Being oriented almost level they were so covered in dirt you couldn't tell they were solar panels.

The inverter is working to this day. The enclosure is housing new batteries and I'm sure the charge controllers are still working as well.

Yea, horizontal panels are little more than shallow sandboxes after a short operation time.
But filling up with dirt and turning into a shallow sandbox, while bad, is probably not (IMO only) the biggest problem.
While sand and dirt can often mostly blow away if dry, dew often collects on panels, even in dry climates, particularly in areas with clear nite skies and low effective radiant sky temps that are well below the ground level dew point temps.

With low gravity induced runoff force due to low or close to zero slope, the dust and dew mixture never runs off completely, dries up in the morning, cements itself onto the glazing, builds up quickly and is mostly not removed when a regular rain comes along. The small (~ 1/16" or so high frame edge lip around most panels is all that's needed to trap any condensate in low slope applications.
I believe that condensate situation is also responsible for the bathtub ring that's often seen on the lower quarter or third of a lot of 20 degree or so sloped panels. The condensate runs down the panel but as it takes some of the accumulated dust with it on the way, the mixture viscosity goes up and the liquid doesn't flow as well and tends to slow down of stop on the lower portions of the panel, and the cycle continues.

So, overall, it may be dew mixed with dust that's the bigger fouling problem which is not to say that it's the only problem.
I've got a couple of owl boxes on my property and owl skrocks on panels need special treatment, especially when they contain what appear to be gopher guts.
strafing runs by buzzards aren't much fun either.

Also, I'd suggest that the rate of panel fouling is perhaps a relatively strong function of panel slope. For example, windows which are usually vertical then to stay relatively clean. Clear skylites tend to get dirtier. Translucent skylites probably get just as dirty but hide it better.

[foxxxnick]

I often wait for rain to clean up. Never hired a professional cleaning staff.

[J.P.M.]

I often wait for rain to clean up. Never hired a professional cleaning staff.

Which is the usual and common way to keep an array reasonably clean.
But if it doesn't rain for half a year in any appreciable quantity as is common in the SW U.S., hitting the array ~ 1X/month with tap water from a hose can go a long way toward cleanliness.
Paying to have a residential array cleaned is a non-cost effective ripoff.

[SolTex]

Second, the hard water spots left behind by tap water and drip drying may seem unsightly but do not seem to inhibit performance restoration in any way I've been able to measure. In other words, using D.I. or distilled H2O is a waste of money and resources.
It also turns out (perhaps serendipitously) that films of Group II chemicals that are responsible for most hard water and hard water spots (mostly Magnesium and Calcium) are pretty transparent to wavelengths of sunlight below ~ 1.15 or so micrometers - about the same cutoff wavelength for silicon hole pair formation - which in plain language means water spots don't matter for PV production if silicon bases cells are used.

Many thanx to J.P.M. for the explanation of why hard water spots are not a problem.
We live in desert West TX and our panels are ground mounted out behind our house, facing true south and tilted 25 degrees from horizontal. We have no trees near the panels so no problem with tree sap or leaves. Other than some infrequent bird poop, the only thing that fouls our panels is blowing dust. I have been depending on the occasional rain shower to help clear the panels, and so far it has worked pretty well. I have avoided trying to wash our panels because our (private well) water is VERY hard. I was afraid that it would leave the panels covered with spots. But now, having read (above) that the spots would not be a problem, I feel better about trying a wash job some time...perhaps in the fall when it is cooler.

[littleharbor2]

Many thanx to J.P.M. for the explanation of why hard water spots are not a problem.
We live in desert West TX and our panels are ground mounted out behind our house, facing true south and tilted 25 degrees from horizontal. We have no trees near the panels so no problem with tree sap or leaves. Other than some infrequent bird poop, the only thing that fouls our panels is blowing dust. I have been depending on the occasional rain shower to help clear the panels, and so far it has worked pretty well. I have avoided trying to wash our panels because our (private well) water is VERY hard. I was afraid that it would leave the panels covered with spots. But now, having read (above) that the spots would not be a problem, I feel better about trying a wash job some time...perhaps in the fall when it is cooler.

I use one of those 12" scrubby/squeegee type window cleaners I found at Home Depot.. If you can squeegee the panels dry, it shouldn't make any difference if your water is hard.

[J.P.M.]

Many thanx to J.P.M. for the explanation of why hard water spots are not a problem.
We live in desert West TX and our panels are ground mounted out behind our house, facing true south and tilted 25 degrees from horizontal. We have no trees near the panels so no problem with tree sap or leaves. Other than some infrequent bird poop, the only thing that fouls our panels is blowing dust. I have been depending on the occasional rain shower to help clear the panels, and so far it has worked pretty well. I have avoided trying to wash our panels because our (private well) water is VERY hard. I was afraid that it would leave the panels covered with spots. But now, having read (above) that the spots would not be a problem, I feel better about trying a wash job some time...perhaps in the fall when it is cooler.

You're most welcome.

Having passed through and spent some time in/around W. TX. I appreciate your dearth of trees.

If the hard water spots are still objectionable for some reason, try a final rinse with vinegar using a hose attachment of the type seen on late nite TV that's used to clean houses and cars, etc. Just make sure there's some vinegar left in the reservoir when you're done, otherwise you'll be reapplying the hard water.
Also, do not use a power washer.

[J.P.M.]

I use one of those 12" scrubby/squeegee type window cleaners I found at Home Depot.. If you can squeegee the panels dry, it shouldn't make any difference if your water is hard.

I've got one of those too, but I found the 18" width gets most all of a 1m wide panel with 3 passes (including some overlap) and saving some time, for not much more $$ spent. Then I discovered by measurement and analysis that squeegeeing didn't make any difference in system performance in any way I could measure over the simple drip-dry method after hosing down the array, especially when I figured out that my array will look (and well on its way to being about as fouled ) about the same a week or two after any treatment.
squeegeeing is also a rather laborious process that's a lot more involved than simply hosing the array, especially for those who are afraid of or unable to get on a roof.

I'd guess most folks with rooftop arrays that chose to try to maintain some level of performance by some regular (and more cost effective) cleaning would probably opt for what's easy, achievable and practical rather than pristine, especially when the pristineness of the array will be gone in a week or two anyway, especially when considering the array will be clean and pretty much spot free after the next decent rain (at least for a week or two).

After all's said and done, an array on a roof doesn't need to be as sharp looking as a car that just got detailed - it's an appliance after all, not a fashion statement.

[littleharbor2]

squeegeeing is also a rather laborious process that's a lot more involved than simply hosing the array, especially for those who are afraid of or unable to get on a roof.

.

I do have easy access to my panels so no big deal to squeegee them off. If they were on a pitched roof with little walking area, they would have to wait for the rain.
BTW I recently got a cordless, battery powered pressure washer. It's not the most powerful washer by a longshot but it does make washing my panels a bit easier.

[J.P.M.]

I do have easy access to my panels so no big deal to squeegee them off. If they were on a pitched roof with little walking area, they would have to wait for the rain.
BTW I recently got a cordless, battery powered pressure washer. It's not the most powerful washer by a longshot but it does make washing my panels a bit easier.

I wouldn't pressure wash any PV panel. It'll increase the likelihood of damage to the edge seals, particularly if the panels are a few or more years old.
I know pressure washers can have a high reach and do a large area quickly but given the potential problems including possible warranty claim denial, it ain't worth it for normal cleaning situations.

[littleharbor2]

I wouldn't pressure wash any PV panel. It'll increase the likelihood of damage to the edge seals, particularly if the panels are a few or more years old.
I know pressure washers can have a high reach and do a large area quickly but given the potential problems including possible warranty claim denial, it ain't worth it for normal cleaning situations.

I guess you'd need to see this cheapie battery powered one in action. It is too weak to do any damage but great for wetting and rinsing the panels.

[scrambler]

I am using a wand extension on my garden hose with the Mpac pulsating head.
Melnor M-Pact Extension Wand MP89905-HD - The Home Depot

This is not high pressure (just hose pressure), but the pulsating jet creates enough impact to loosen bird poop without being more strain on the panel that a rainstorm.

Once or twice a year is all I have needed to remove the poop and pollen accumulated during the dry season.

The only time I had to actually brush the panel was the year of the massive fires that deposited a thick layer of soot on the panels....

[J.P.M.]

I guess you'd need to see this cheapie battery powered one in action. It is too weak to do any damage but great for wetting and rinsing the panels.

I guess the words "pressure washer" are what raised the flag for me. I'm just an old school hoser I guess.

[azdave]

We finally had measurable rain last night for the first time in 124 days. It rained for about 10 minutes and then it was over. Rain gauge reported 0.08" inches. Panels cleaned. Your results may vary.

[J.P.M.]

We finally had measurable rain last night for the first time in 124 days. It rained for about 10 minutes and then it was over. Rain gauge reported 0.08" inches. Panels cleaned. Your results may vary.

Any difference in output that you could attribute - anecdotally or otherwise - to the rain ? Both days about the same cloudiness and/or air temp ? Gifferent wind regimes for the days ? How much different did the panel glazing look ?

Thanx.