How do you clean your panels?

[J.P.M.]

I am surprised no one has mentioned RV power washers. Stores like Lowe's and Home Depot sell them. They are just a hose nozzel that compresses the water acting like a power washer. This is important because if your solar panels are 20 feet high like mine water pressure will be low. It also extends up to 6 feet making it perfect for cleaning all of the solar panels. An example of one of these RV cleaners is "Orbit Telescoping Cleaning Wand". I bought something similiar at lowes for $12 and it power washed 80 pounds of bird poop off my roof. It did the best job.

The argument that rain is all you need to clean solar panels is rain is stupid because birds will poop on them, there will be dirt on other debris that easily doesnt come off with rain. You need to power wash them.

I've found rain to be comparable to simple hosing and that simple hosing can restore most of the production lost from the usual types of array fouling that I, and I suspect most folks get - in SO CA anyway.

Power washing panels may seem the manly thing to do, but it's simply a bad idea. It may break the seal between the panel and the glazing. It also may void a warranty. It's also overkill. Simply hosing off panels will remove enough of the fouling to restore about 3/4 of the performance lost to fouling.

As for rain and it's efficacy, I've got a fair amount of data for my array that shows precipitation can be an effective way to clean an array. Depending on how long, how sustained and how intense, precipitation can restore somewhere between, say, maybe 25 -50 % of the lost performance for, say 0.25" precip., to restoring virtually all of the performance for a something like a hard, 2 day soaker. Amounts are hard to quantify. Generally, and up to a point, more liquid for a longer time leads to more performance restoration. High velocity from high pressure doesn't get better results - just more chance for water ingress.

Perhaps interestingly (or not), and maybe a little off topic, I get a fair amount of fog/dew overnite - enough to register precipitation of ~ 0.01" to, say, 0.03 " - the kind that leaves the driveway wet and windshields dripping. After measuring array performance for 4+ years, under clear skies on consecutive days on either side of such a fog event, my array fouling always calcs/measures out lower after the fog than before the fog. How much lower varies, but always lower.

Simply hosing my array at a rate of ~ 3/4 gal./panel from above (north of) the array and letting it drip/air dry seems to restore about 3/4 of the lost performance so that, for example, A condition of a 10 % performance loss to fouling may get reduced to, say, 2 - 3 % or so from such a hosing. To get the array all the way clean takes a hosing, dish soap and a SOFT cloth followed by a hose rinse.

Without rain or rinsing, my array seems to foul at a rate that causes production to fall at an approx. rate of about 0.75% to about 1.0% per week. It also seems to level off at roughly about 8 to 10 % after 2 or 3 months. I've theorized that the dew I mention above may have something to do with that asymptotic leveling off but I haven't figured out a way to determine if my hunch has any validity and if so, how.

I've also found that soaping and rinsing with hose water and leaving hard water spots vs. soaping and rinsing with distilled water and wiping the array dry so that no water spots remain produced no discernable or measurable difference in array output or performance. Simply put: If there is an advantage to using D.I. or distilled H2O over tap water, I can't measure one.

[Mike90250]

If you like taking a risk, you can use a power washer on your panels. I would recommend against it. Panel seals are designed for rainfall, not power washing, and once you blow the seals and water gets in, your panels are toast.

[littleharbor]

80 pounds?? How did you figure that out?

[solar pete]

howdy friday and welcome to spt. i do disagree with your asertion that you need to power wash panels as i know for a fact that you dont. now bird turds can be an issue but a spray with the hose has always worked for me and i have been tols by several manufacturers not to use any detergent or chemical of any kind just water and a soft cloth

[Friday]

I am surprised no one has mentioned RV power washers. Stores like Lowe's and Home Depot sell them. They are just a hose nozzel that compresses the water acting like a power washer. This is important because if your solar panels are 20 feet high like mine water pressure will be low. It also extends up to 6 feet making it perfect for cleaning all of the solar panels. An example of one of these RV cleaners is "Orbit Telescoping Cleaning Wand". I bought something similiar at lowes for $12 and it power washed 80 pounds of bird poop off my roof. It did the best job.

The argument that rain is all you need to clean solar panels is rain is stupid because birds will poop on them, there will be dirt on other debris that easily doesnt come off with rain. You need to power wash them.

[carmelinasweeney]

Solar panels get cleaned when it rains. It is easy to maintain and does not require much in terms of deep cleaning. But if the panel is situated in a place that is prone to dry weather or dust storms, it needs deep cleaning. The cleaning process is quite simple and can be done using a hose and a bucket of soapy water. While cleaning, take care to use a non abrasive sponge though to prevent damage or scratches to the panel.

[J.P.M.]

The 60% thing had nothing to do with how clean the panels are. It was simply a comment that I was getting 60% of rated power yesterday. The 21 panels I have are rated at 300 watts each. My inverter was showing it was producing almost 60% of the rated capacity. I understand that achieving 100% of rated capacity almost never happens.

My panel cleanliness comments are not scientific. It is simply me standing on the ground and looking up at the panels. A week ago I looked at the panels and it was obvious they were dirty as they had streaks of dirt on them. It was the same dirt they had on them when installed. Yesterday I looked at the panels again and the streaks of dirt were gone. The only change is we got 8" of snow on Monday and it was all melted off the panels by yesterday morning.

Today was mostly sunny at my location. My array produced 60% of its STC rated output at 1010 and 1425 hrs. today. At 1220 hrs. today it was producing power at about 76 % of rated output. It's about 2 % fouled at this time. It rained 2 about weeks ago. Before the rain the array was about 8 % fouled.

The effect precipitation will have on an array's cleanliness will vary greatly with the type, amount, intensity and duration of the precipitation.The effect precipitation will have on an array's output will not be as noticeable as other factors that influence performance.

[reader2580]

60% of rated power is a nice number, whatever that means, but without a lot of other information it doesn't mean much, nor is it possible to infer much about array cleanliness from it.

The 60% thing had nothing to do with how clean the panels are. It was simply a comment that I was getting 60% of rated power yesterday. The 21 panels I have are rated at 300 watts each. My inverter was showing it was producing almost 60% of the rated capacity. I understand that achieving 100% of rated capacity almost never happens.

My panel cleanliness comments are not scientific. It is simply me standing on the ground and looking up at the panels. A week ago I looked at the panels and it was obvious they were dirty as they had streaks of dirt on them. It was the same dirt they had on them when installed. Yesterday I looked at the panels again and the streaks of dirt were gone. The only change is we got 8" of snow on Monday and it was all melted off the panels by yesterday morning.

[J.P.M.]

The rain this fall didn't clean off the panels. I noticed yesterday that since the 8" of snow from earlier in the week melted off the panels look a lot cleaner from the ground. I was getting almost 60% of rated power yesterday. I think that is pretty good considering the time of year and the angle of the panels.

60% of rated power is a nice number, whatever that means, but without a lot of other information it doesn't mean much, nor is it possible to infer much about array cleanliness from it.

[reader2580]

The rain this fall didn't clean off the panels. I noticed yesterday that since the 8" of snow from earlier in the week melted off the panels look a lot cleaner from the ground. I was getting almost 60% of rated power yesterday. I think that is pretty good considering the time of year and the angle of the panels.

[J.P.M.]

Well you confused us again.

I know you meant to say dish soap is an aggressive soap (which I can agree with) but it is not an abrasive soap.

I still vote for rainwater applied by mother nature. If you have soft water that would be my next suggestion. That is what works for my panels on my house. "Your mileage may vary."

For most situations, I'd probably vote the same. Regular rain is probably the best combination of ease and cost to keep an array clean. However, the weather may not cooperate to make life easy. As you write, Your mileage may vary.

Provided the panel or array is tilted at something > 10 deg. or so to the horizontal, depending on its intensity and duration, a decent rain may restore ~3/4 to 90% + of the clean performance of a panel or array that has been lost due to fouling, maybe all of it.

If regular rain of some consequence, maybe like about an inch/month or so can be counted on, that'll probably help to hold the overall fouling penalty to maybe 3% +/- a bit.

If performance decreases at a rate of something like 1 %/week without rain or cleaning, it'll be hard to justify any mechanical/artificial means of cleaning if an area gets, say, maybe 15" or more rain/yr. provided there is no dry season. 1X/month hosings can probably keep things reasonably clean enough during extended rainless periods or dry seasons.

A bit off topic: I could see some adjustment to hosings in a place like Albuquerque. Winter is the dry season and temps. there in the A.M. - both the ambient air and radiant sky temps. can be and often are well below freezing with array glazing temps. less than the air temp. That would make the temp. diff. between the glazing and hose water enough to crack the glazing. Not much of a consideration for most of us, but may be a consideration in cold, dry climates. The situation then becomes a guessing game at glazing temp. as f(P.O.A. irradiance). Not a crisis, at least not until glazings start cracking from thermal shock.

[azdave]

Sorry if I confused anyone.

Well you confused us again.

I know you meant to say dish soap is an aggressive soap (which I can agree with) but it is not an abrasive soap.

I still vote for rainwater applied by mother nature. If you have soft water that would be my next suggestion. That is what works for my panels on my house. "Your mileage may vary."

[ButchDeal]

Dish soap is an abrasive soap to help clean pots and pans.

Are you confusing some other type of soap with dish soap?

Most that I am familiar with will cut grease but are not abrasive. Thats why you have a scouring pad.

an example of "dish soap" https://dawn-dish.com/en-us
Dawn is NOT an abrasive, Dawn is a surfactant.

[frankiek3]

Dish soap is an abrasive soap to help clean pots and pans. I'm not going to recommend using it for solar panel cleaning, but to each their own. I'll fix the cut off, the manual recommends a mild detergent if not just water.

Actually many companies make protective coating products for solar panels. I'm not aware of manufacturers that do, and I guess I wrote that thinking of when dish soap is used to wash a car it will remove any wax exposing the clear coat. Sorry if I confused anyone.

[azdave]

frankiek3,

We know solar panels have a special coating on the glass but your dish soap warning kind of made it sound like you thought some brands of dish soap leave behind a protective coating harmful to the glass. I knew what you meant but I doubt any kitchen dish soap would ever be an issue.

I use rain to clean my panels. I just can't always schedule when it will fall.