Advice on cleaning PV panels

[silversaver]

Best of luck my ass. Only a moron would spray water on a panel when the sun is shining.

+1


lately I have been reading noob starting business without proper knowledge of business they are after.

[J.P.M.]

FWIW, as my panel fouling research continues, I become more convinced that my array, in a semi rural area, without rain of some sort, loses performance due to fouling at an approximate rate of about 1% per week.

A rain of, say, .25" or so will restore about 2/3 of the accumulated performance deficit. So, 6 weeks after a wash, without some precip., there's about a 6 % performance penalty. If it then rains, about a 4% improvement down to about 2% dirty or so. 4 more weeks after that, about a 6% penalty (the remaining 2% + 1% for each of 4 weeks). After all this measuring is done I'll probably hose down the array with a hose (IN THE EARLY MORNING !!) about 1X/month or a month after a sig. rain, and wash it at each equinox.

Without washing, I believe that the rate of fouling will become asymptotic at somewhere between 10 and 12% for my location, but don't have enough long term non-rain conditions to say much that's substantive on that (yet).

Two other points:

I see no quantifiable benefit to D.I. rinse. If it exists, it's too small for me to identify. I washed and rinsed w/plain H2O, Washed and rinsed w/D.I. water, and also washed and rinsed with regular water during a continuing rainstorm (03/01 +03/02/2015) and the next fouling measurements showed no quantifiable diff. between the three methods.

I'd add that due to instrument limitations, about the best I can claim is about +/- 1 to 1.5% or so in accuracy if I'm careful and lucky, maybe a bit better on precision which is one reason why all this is an approximation, perhaps made better by consistent repetition on clear, cloudless days.

Also, morning fog that results in measureable precip. in the rain gauge tends to mud and cake things up some on the entire panel, particularly at the lower 10"-12" of a panel. That's a pretty common sight around here and I expect elsewhere as well.

Take what you want of the above. Scrap the rest.

[Mike90250]

re-posting a safe, cheap method

Look at the Mr Clean Car Wash kit, and it's DI water filter cartridge. Forget the soap. Wash with plain tap water in the AM, before the sun hits them (cold water & hot panels = damage) and then rinse with the DI (spot free) feature. You can get the rinse DI refills @ amazon or ebay.

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

mr-clean-auto.jpg

[pleppik]

Wash with plain tap water in the AM, before the sun hits them (cold water & hot panels = damage) and then rinse with the DI (spot free) feature.

Just out of curiosity, has anyone ever heard any actual reports of panels getting damaged because they were hit with cold water during the daytime?

It seems to me that if this is a real risk, then it would also happen if there was a sudden rainshower on a sunny afternoon.

Here in the midwest, in the summer we can get isolated convective showers in the afternoon where it will be bright sunshine right up to the moment when the rain hits the ground. I've certainly never heard of a solar panel breaking because of an afternoon rainshower.

[DanKegel]

No, but when I was a kid, I broke our 1967 Ford station wagon's windshield by spraying it with a hose on a hot day in Seattle.

I remember watching that crack creep across the windshield with a sense of dread.

[J.P.M.]

Just out of curiosity, has anyone ever heard any actual reports of panels getting damaged because they were hit with cold water during the daytime?

It seems to me that if this is a real risk, then it would also happen if there was a sudden rainshower on a sunny afternoon.

Here in the midwest, in the summer we can get isolated convective showers in the afternoon where it will be bright sunshine right up to the moment when the rain hits the ground. I've certainly never heard of a solar panel breaking because of an afternoon rainshower.

I have a feeling those showers happen in other parts of the world as well. As do hailstorms and hurricanes. Every situation is different. The probability of a panel cover cracking due to thermal stress is unknown to a large degree, but hitting a hot panel with a hose seems a moron's invitation to a disaster.

Why take the chance ?

Talking about dimensional changes, when things like glass fail in such situations as being discussed here, usually and often the failure is caused by a sudden dimensional change of a PART of the light of glass relative to some other PART of the light, not necessarily because of edge constraints.

BTW, thin(ner) glass has some minor advantages in this respect, as does low iron glass to a greater degree because it runs cooler (less absorption of solar irradiance --->>> cooler operating temps).

A rainstorm, even a deluge, USUALLY produces a more uniform temp. change across the entire light of glass. That mitigates the differential expansion within and across the glass to a great degree. A hose usually/often hits one part/portion of a light and not other portions first, and usually with large amounts of water. It's the internal differential dimensional change of a relatively brittle material that lacks a predictable "yield" point and goes immediately to brittle fracture/failure over a "short" time that causes all or most of the problems.

[pleppik]

I have a feeling those showers happen in other parts of the world as well. As do hailstorms and hurricanes. Every situation is different. The probability of a panel cover cracking due to thermal stress is unknown to a large degree, but hitting a hot panel with a hose seems a moron's invitation to a disaster.

Why take the chance ?

It just struck me that "don't wash your panels during the day" is pretty much forum-standard advice, but I'd never heard of anyone actually damaging their panels this way. It seems logical that it could happen, but the more I thought about it the more it seemed that any module design likely to break in this way would probably shatter from natural causes long before its 25-year design life.

There was even a guy in Australia who posted videos to this forum a few months ago of a water cooling system for his modules, and he didn't seem to have a problem with breaking panels. So is "don't wash your panels during the day" just an urban myth, or have there been actual solar modules shattered from heat stress?

I've heard that there are some commercial and utility-scale arrays where they regularly wash the panels. I wonder what protocols they've put in place?

[silversaver]

Like most substances, glass expands as it heats up and shrinks as it cools. It also has moderately low thermal conductivity. And it's hard but brittle. These three facts are why glass can crack when suddenly cooled. Sudden changes in temperature are commonly known to cause glass (and other materials) to break.

most or all panels are with tempered glass which is fine, but I rather not take the chance.

[J.P.M.]

It just struck me that "don't wash your panels during the day" is pretty much forum-standard advice, but I'd never heard of anyone actually damaging their panels this way. It seems logical that it could happen, but the more I thought about it the more it seemed that any module design likely to break in this way would probably shatter from natural causes long before its 25-year design life.

There was even a guy in Australia who posted videos to this forum a few months ago of a water cooling system for his modules, and he didn't seem to have a problem with breaking panels. So is "don't wash your panels during the day" just an urban myth, or have there been actual solar modules shattered from heat stress?

I've heard that there are some commercial and utility-scale arrays where they regularly wash the panels. I wonder what protocols they've put in place?

Tell you what: wait for a 90 deg. F. day with clear skies and no wind, then go hit your panels with full flow from a hose about 2 P.M. and report back on the results.

[bcroe]

[QUOTE=pleppik} "don't wash your panels during the day" is pretty much forum-standard advice[/QUOTE]

Maybe standing in water washing a system operating at 400 volts is a dangerous thing to do?
Bruce Roe

[silversaver]

Maybe standing in water washing a system operating at 400 volts is a dangerous thing to do?
Bruce Roe

no really.... when there's enough lighting, the voltage is already there.

[Mike90250]

Over the years, I've seen many cars with a single stress crack across the windshield. one out of 10,000 maybe. It does not happen often, but why invite it happening at all? Early morning, with dew still on the panels, the crud is soft and washes off easily. I have pond water, no mineral content, and so here I can skip the DI rinse. While in Los Angeles, I had to use the DI rinse.

[DanKegel]

What happened without the DI rinse?

[bcroe]

no really.... when there's enough lighting, the voltage is already there.

Does that mean there is no danger? Or, that there is no time when there is less danger?

I can look out the window and tell when the system is producing 7000 watts or 20 watts.
I have actually gone out and measured voltages at night, seeing less than 10 volts,
have you? Bruce Roe

[bcroe]

Dummy Short for Washing

I'm thinking, maybe there ought to be equipment for people who want to wash panels
at night. Open the double pole disconnect switch, close a dummy shorting load to
clamp the voltage. This load might have LED or other indicators to indicate the level
of any continuing potential. Bruce Roe