Cleaning Solar Panels.

[Yaryman]

I read the thread asking how. Just wondered if the method mentioned in this video is acceptable?

Why clean my panels? They have only been up for 10 days, but I caught the first rain after summer which brought down all the dirt in the air.
I have a housing development going in across the way, and it has been throwing up a quite of bit of dirt. Here's one of my dirty panels.



Here's the video. Not sure if using squeegee is OK, but my tap water does leave spots. So cleaning off the dirt, and then leaving spots isn't desirable.

[Mike90250]

I would never scrub panels unless it was the only way to de-gunk them. I just use a hose and spray them, but I have soft rain water. If you have hard water, the Mr Clean Car Wash kit has a DI rinse cartridge that gives a spot free rinse.

[J.P.M.]

FWIW:

When I clean my array, I use kitchen dish soap ( ~1/4 tsp. to a bucket of H2O) with a soft cloth over the brush. I wash in both directions, horizontal, then vertical, rinsing after each wash as I go, and squeegeeing after the last rinse in the vertical direction, top of array to bottom.

I too get some spots.

My contribution to this discussion:

Those panels in the video don't appear to have an anti reflective coating (ARC) which is probably good, because the bristles on the brush used may damage the coating. Many/most PV panels have ARC coating. Use a cloth and not much pressure and avoid possible damage to the ARC. Also, the video was done at a time when sunlight may have raised the glazing temp. BAD IDEA - APPLY WATER ONLY IN THE EARLY A.M. BEFORE THE GLAZING HEATS UP, OR LATE P.M. AFTER THE GLAZING HAS COOLED.

On D.I. vs. tap water: My experience after doing the same cleaning method described above 4 or 5 times using tap water and on 2 occasions with Mr. Clean D.I. method, I cannot measure any improvement in array performance - tap H2O to D.I. rinse - that I'd attribute to the spots not left by the D.I. water. I believe the human eye, beyond obvious crud and crusted stuff, is a poor indicator of how much, and in what ways, dirt impedes transmission of solar irradiance.

It may be a cosmetic thing and so be it. By my estimate, and in any case, I cannot measure the decrease in performance due to dirt (fouling) more accurately than ~ 0.75% or so , and my array seems to foul at a rate such that performance decreases ~ 1%/week or so w/out rain, depending on conditions of dust/wind/events/etc. Given that estimate, and again, for my location, conditions and situation only, after a week or so, any (perhaps small ?) diff. in performance due to the diff. between using D.I. or tap H2O would be masked or made effectively insignificant after about a week or so.

BTW, a decent rain - roughly 0.3 - 0.6" (or so) of some intensity or duration seems to restore about very roughly 2/3 to 3/4 of the performance lost by accumulated dirt. So, for example, starting with a clean array. After 4 weeks of no rain, array performance may decrease by 4% or so. A decent rain may restore ABOUT 2 or 3 % of that reduction. This is not an exact science. I do believe (speculate actually) there may be some sort of asymptotic behavior to the performance decrease as f(time,conditions), but don't have enough data to SWAG it yet. That is, the rate of performance decrease may become less over time between rains events and perhaps reach some point where the rate of decrease levels off or effectively stops. Not to oversimplify too much, but I can't see where a year without rain would impair performance by 52%. Maybe, but I'd need to see data to believe that one. At this time, depending on rain, and how the fouling measurements are going, I hose my array w/ tap water about every 4 weeks or so and resign myself to about a 2 - 3% fouling penalty.

[solar_newbie]

Yaryman. Could you update what the option you choose for cleaning those panels? I like to set quarterly panel clean if possible and try to learn until the first one due.

[Yaryman]

Yaryman. Could you update what the option you choose for cleaning those panels? I like to set quarterly panel clean if possible and try to learn until the first one due.

I haven't decided on a method yet.

I think the best method might be to clean them off while it was raining so the dirt would be gone and their would be no spots from the water.

BUT, I'm not going to wait for the rain. At some point I will go to home depot and see what they have that I can put on a extension pole.

[woodtiger]

How often do we wash it if it doesn't rain in Socal?

[silversaver]

I just hose them down with soft water. no water spots. Maybe twice per year, that is really what you need to do besides the rain.

[solar_newbie]

I just hose them down with soft water. no water spots. Maybe twice per year, that is really what you need to do besides the rain.

Where to get "soft water"? My tap water gives spot when washing my cars without wiping dry..

[silversaver]

Where to get "soft water"? My tap water gives spot when washing my cars without wiping dry..

water softner

[solar_newbie]

water softner

It eats space in the garage next to the water heater . It is no go for me. The water is not that hard to be needed.

[J.P.M.]

How often do we wash it if it doesn't rain in Socal?

I belive hosing them off every 4-6 weeks in the absence of rain will hold my performance degradation to about 3 % average or so. Your mileage will vary.

Also, as written, I can't measure a difference in performance due to water spots.

[Mike90250]

Where to get "soft water"? My tap water gives spot when washing my cars without wiping dry..

MR Clean Car Wash Kit has a DI rinse cartridge.

http://www.amazon.com/Mr-Clean-AutoDry-System-Starter/dp/B0006M56CE

Just hose the dirt off the panels, and then a rinse with the treated DI water.

Do it in the AM, when the panels are cool, and maybe pre-dampened from dew

[bcroe]

MR Clean Car Wash Kit has a DI rinse cartridge.

http://www.amazon.com/Mr-Clean-AutoDry-System-Starter/dp/B0006M56CE

Just hose the dirt off the panels, and then a rinse with the treated DI water.

Do it in the AM, when the panels are cool, and maybe pre-dampened from dew

Better yet, do it in the middle of the night, so they can't kill you. Bruce Roe

[solar_newbie]

Better yet, do it in the middle of the night, so they can't kill you. Bruce Roe

Why they kill you ? Just turn off the breaker, no electric will be in those panels right ?

[inetdog]

Why they kill you ? Just turn off the breaker, no electric will be in those panels right ?

Wrong! Turning off the breaker just means that the panels are not supplying power to a useful load. There is still plenty of DC voltage on the panels. In the case of a grid tie system it could be as much as 400V DC, or even higher in unusual cases.
You can hope that the insulation on the wires is all good even after you soak it with water. And the water will not be a good conductor.
Some experiments have shown that even if you use salt water for conductivity you do not get a dangerous current path if the water stream has broken up into droplets by the time it hits the voltage source.
Do not try this with high voltage (power transmission lines) though.