Washing panels revisited.

mcgivor · December 2016

Looked back on posts and comments regarding washing panels, there were various opinions on what or what not to use to clean with but nothing with measured performance gains, so today I conducted an experiment to see for myself. Recently there has been an escavator working upwind creating dust which had left a light coating, not enough to see from a distance but visible close up.

Took a current reading before and after each panel was washed using plain water and a sponge/squeegee. Did this in the morning before they are too hot, each panel read 3.4A to 3.6A before washing and post wash measured 4.7A to 4.8A. readings taken 30 second after wash. Took another reading 15 minutes later to confirm the cooling effect didn't skewer the results, the readings were the same as the post wash, so a gain of around 1.1 amps per panel, that is a 30% improvement in peformamce.

One member claimed that anything other than leaves or shadows was negligible and washing was not necessary, I beg to differ, personally I like to put figures behind my claims if possible, hense the experiment. So my opinion is to keep panels clean for best peformamce.

mike95490 · December 2016

In the morning,as the sun rises, power is going to increase. 15 min shows up in my logging,

mcgivor · December 2016

mike95490 said:

In the morning,as the sun rises, power is going to increase. 15 min shows up in my logging,

Understandable, they were in fact a little higher but only about 0.1A per panel, and there is the question of clamp on ammeter deveation, collectively over the array that would be noticed more, in my case the post wash current was 10A higher.If only I could stop the world from revolving for 15 nimutes.

westbranch · December 2016

Mid day, High Noon , should give more repeatable results... but you would have to negate the morning incoming solar (cover the panels) to keep the temp down

BB. · December 2016

"Cooling" will affect Vmp (assuming MPPT based controller). Imp/Isc current is much less affected by temperature (and Imp/Isc very slightly drops as panels cool). So array current would be the optimum to see how much improvement you get from washing.

Doing the test around solar noon would make sun positioning less of an issue.

-Bill

mcgivor · December 2016

The morning was chosen as it was cool, 25 deg C same temperature as the water used, have read that it's not advisable to wash when hot, must admit i didn't think of shading as westbranch suggested. The result supprised me though and along with all the other maintenance this will become yet another task, when off grid it is a marrige with your system, you have to keep it happy, or so I have learned.

jimmyaz · December 2016

While I agree that a cleaner panel would surely give a slightly more power. But I don't think 30%. I have done this many time, since my panels are on the ground. I clean one set and run right in to see if it increase much.... but it only increase 5-10 watts for 600watts rated panels.

But well, this is all depend on how dirty the panels is... hard to say.

dexter12353 · June 2017

This is part of our struggle on our property...we have quads and side-by-sides so every time some friends come over and ride around for a few hours my 1000w of panels are usually covered pretty thick...If only there was a system that washed them automatically.....

luckily my system is a tracking system and I can set the panels in a vertical position and just stand in front of them to clean them. I'm glad I didn't put all my panels butted against each other otherwise I'd probably have to walk on them to clean them....

dennis461 · June 2017

Just washed mine today, sun almost set; dish detergent in a garden sprayer. Pollen has been real bad here, I do see a difference in power output I think it was around 10-20%. I've got large oak and other hardwood trees. Most times I just use water sprayed from the ground. When using the soap, my sprayer is low pressure and I climb up on the roof (single story.). I also keep a hose on the roof.

dexter12353 · June 2017

dennis461 said:

Just washed mine today, sun almost set; dish detergent in a garden sprayer. Pollen has been real bad here, I do see a difference in power output I think it was around 10-20%. I've got large oak and other hardwood trees. Most times I just use water sprayed from the ground. When using the soap, my sprayer is low pressure and I climb up on the roof (single story.). I also keep a hose on the roof.

do you dry off your panels? I was thinking any minerals in the water would cause hard water spots on the panels...Do you have those kinds of issues?

dennis461 · June 2017

dexter12353 said:

dennis461 said:

Just washed mine today, sun almost set; dish detergent in a garden sprayer. Pollen has been real bad here, I do see a difference in power output I think it was around 10-20%. I've got large oak and other hardwood trees. Most times I just use water sprayed from the ground. When using the soap, my sprayer is low pressure and I climb up on the roof (single story.). I also keep a hose on the roof.

do you dry off your panels? I was thinking any minerals in the water would cause hard water spots on the panels...Do you have those kinds of issues?

I have city water for this job (well water for specific uses.)
Bird poop spots get removed from washing, panels look clean without hard water spots.
Tried a brush/water applicator once but started to think I could scratch them if not real careful. Drying might create a problem with scratches also.

And again, this is not a regular task, only when pollen collects and is not removed by rain.

mcgivor · June 2017

Washing a ground array is no big deal, in the dry season I wash mine about once per month with a sponge/squeegee and plain water, takes 10 minutes, just a form of general maintenance. Rainy season it pretty much rains every night so no need then, but if I had mounted on athe roof, which was tie initial plan, they would probably never get washed, my choice to go ground was more for electrical maintenance reasons and I have plenty of space. Some information in link.
https://evergreensolar.com/how/cleaning/

Lumisol · June 2017

Adding one extra panel to the array would add more than enough to offset the need to wash the panels it seems. I'd rather add a panel than fall off a roof and be out of commission for a period of time. It's like the old to track or not to track debate. The cost of a good tracking set up will be more than adding a panel in a lot of cases and will not net any more power.

dennis461 · June 2017

Lumisol said:

Adding one extra panel to the array would add more than enough to offset the need to wash the panels it seems. I'd rather add a panel than fall off a roof and be out of commission for a period of time. It's like the old to track or not to track debate. The cost of a good tracking set up will be more than adding a panel in a lot of cases and will not net any more power.

This is OK for new or flexible systems. However. I thought the discussion was, should an existing system be washed.
In my case, grid tied, I installed largest system allowed by utility based on my electrical KWH usage from previous 365 days, (prior to design).

So it's obvious to all of us, clean panels are providing more power than dirty panels, all other parameters being equal, weather :-) it's 1% or 30% is probably debatable without hard data.
Sure, falling off a roof has it's drawbacks (I googled it), so it is not in my plan.

littleharbor2 · June 2017

Sure, falling off a roof has it's drawbacks (I googled it), so it is not in my plan.

Did it mention that the fall isn't as bad as the sudden stop at the bottom:

Lumisol · June 2017

LOL exactly, you can fall from miles up without any harm at all. It's that last inch that kills you.

I would think it was obvious without measuring it. Transparent materials transmit more light than translucent ones or opaque ones. Hint: Don't use paint on the panel fronts to get the colors you like to match the house, there are already colored panels available.

mvas · June 2017

This year, rain has kept my panels clean enough until recently.
Saturday, at Solar Noon, I cleaned my panels for the 1st time this year, I gained 10%.
I used warm water to dissolve the crud quickly.
The previous panel was drying before I was even finished with the next panel.

solar_dave · June 2017

The valley of the Sun is quite a dusty place in summer. I only use a hose and water to "rinse" the panels early in the morning to avoid the thermal shock as much as possible.

animatt · June 2017

I believe it is good practice to clean panels with water that is similar in temperature to the solar panel. This usually happens while they are cooler. (not in direct sun).

This can reduce thermal shock to the glass.
Your heating your water first helped.

But throwing bucket of 50f water on a 150f panel is probably not a great idea. Just a consideration for casual readers whom may happen upon this thread.

Lumisol · June 2017

A 100 degree difference won't make a difference really, and the water will reach the temp of the panels almost instantly.
To break a glass, you need to heat it to around 500 degrees and then submerge it in ice water quickly. I used to make glasses out of jars with this method and even then, you need to score the glass heavily first.

animatt · June 2017

What about glass that has imperfections. It may not be visible but why risk it.

I had a car with a small chip /crack in the windshield. One winter morning without thinking I started car up and had heat going to the windshield. When I went back to the vehicle a few minutes later. The small issue I had beckoned now more immediately attention.

You can assume everything works and will work as designed, but why not treat your stuff more gently. Even with a warranty I would rather not deal with that process if I could avoid it.

I guess I error on the side of caution and having good practices. In general I believe those are the things we should promote.

Estragon · June 2017

I'd agree that cleaning panels out of direct sun is wise for a number of reasons.

- hard to clean bird bombs, dead bugs, etc when it dries too fast.
- full sun causes glare and hurts my eyes.
- standing in a pool of water with panels at full current may be safe, but I'm chicken.
- I wilt at much over 75°f. Shade is cool.

@Lumisol is probably right about the panels standing up to the thermal shock. A squall can go from full sun to buckets of cold rain or hail in seconds, which is probably worse. Still, I'd prefer to be elsewhere in the circumstance.

The ability to handle thermal shock likely depends some on the initial state. Strange things happen to stuff at temps <-40°f or so.

Lumisol · June 2017

Ratio absentis, impulsum, quando praecepta

Incidentally, -40 is the same in Fahrenheit and Celsius.

Estragon · June 2017

Wow. Latin. You must be aiming for a wide audience there.

I'm aware of how °c relates to °f. Not everyone here does though, which is why I normally specify.

Lumisol · June 2017

LOL
Latin is after all the base for English, so most know it.
I am not sure they still teach it in schools, but I have taught my kids just as I learned.
I was pointing the temperature thing out to those that did not know it, as you say, not everyone does.

BB. · June 2017

While panels are supposed to be OK to hit with cold water on a hot day--It is not something I would recommend either.

I used to evaluate disc and tape drives decades ago. And just the simple temperature cycling twice a day (within product specification) fairly quick ramps (something like 20 minutes from 40F to 120F)--And within two weeks of this, about 80% of the commercial products (at the time) would fail. Traces delaminate, solder joints fail, flex circuits delaminate, surface mount components pop-off, etc.

Solar panels have lots of laminated layers--And the amount of stress that can happen from shock cooling one side and thermal mass on the other side of a "layer"--Lots of bad things can happen.

Because solar cells are (especially now) extremely thin, and the backing is plastic (with low thermal mass, low heat transfer capability), running a hose on a hot panel is probably not the worst thing that could be done (with a well designed/manufactured panel).

-Bill

Lumisol · June 2017

That's comparing apples to oranges. Did the disks actually break or just become unreadable? In my experience, the discs become unreadable as the data is corrupted by tiny migrations on the surface as the substrate expands and contracts.
That is not a thing that can happen to a piece of glass. If fact, that is the reason that the new data storage methods use glass crystals to store data.

https://www.theverge.com/2016/2/16/11018018/5d-data-storage-glass

It is also not a thing that can happen to the glass over your PV panels. And it's certainly not anything worth worrying about.

Ratio absentis, impulsum, quando praecepta

BB. · June 2017

Mostly, physically broken electrical connections from thermal cycling (not thermal shocks, but reasonably quick ramping of temperature).

- Bill

Lumisol · June 2017

Oh, sorry, I read the other post as discs and not disc drives. Yeah, I'd expect that from a drive too. In normal use they never experience climate changes that fast since they are in a relatively climate controlled setting indoors, a lot different than a panel face up in the sun that gets cold rain dumped on it or hail.

mike95490 · June 2017

I generally wash my panels first thing in the AM, while they are still damp from overnight dew.

Washing panels revisited.

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