Cleaning panels doesn't really matter - measurement and photo

[J.P.M.]

JPM,

I am going to have to disagree with you. I am an old idiot and have recently "discovered" YouTube. I love it. Always good for a laugh or a cringe...

It's not just for the "new idiots"

No, from my experience, it appeals to idiots of all ages and social standing.
But I think I understand what you're writing. I just think that like Mad magazine or porn, taking u-tube seriously can give one a distorted view of reality.

I'm not quite an idiot. At least not yet. I just play one on forums.

A little background. The adjective "new" is meant and used as an adjective to the open compound noun "idiot's bible", not to "idiot's".

When I was a kid, there was (and I believe still is) a publication called the "Reader's Digest".
The common opinion in my town was that if you were too intellectually lazy to read a newspaper or be informed by other reliable means such as reading a book or going to the public library, etc., your search for information quickly devolved to the Reader's Digest. It was seen as the rough equivalent of pedestrian Cliff notes. If you had a short attention span and wanted to sound like you knew something, you might be a Reader's Digest reader.

Thus, the pejorative term for the Reader's Digest that I grew up with and came to use was "the idiot's bible".
Seems to me a lot of the same characteristics apply to u-tube. Hence, "The New Idiot's Bible".

[PNW_Steve]

JPM,

I am going to have to disagree with you. I am an old idiot and have recently "discovered" YouTube. I love it. Always good for a laugh or a cringe...

It's not just for the "new idiots"

[J.P.M.]

> Short term cooling as a benefit to washing an array is small enough to be pretty much non existent and can be ignored.

That's my original point: naive observers on YT and elsewhere can be misled by transient effects.

That's not the way I read your post. If I read something different in it than you intended, my bad inference. Another example of the old wisdom that most problems often have poor communication at their root.

Anyway, not that it matters, but I don't agree with the blanket statement/opinion that seems to be floating about here that cleaning an array is not necessary or productive, but, opinions vary.

On a different subject: If by YT you mean You Tube: I refer to You Tube as the "new Idiots' bible".
It's what happens when the inmates get to talk about how the asylum is or ought to be run.

There was a time when things that could get folks in trouble or worse got vetted. That was when folks with with critical thinking skills made up a greater portion of the population. Now, it's the intellectual equivalent to the wild west.

Mike Judge was interviewed a few years ago. He said that when he wrote the script/story line for the movie "Idiocracy" so that the action and idiocy in the film happened 500 years in the future, he didn't think his timeline would be off by at least an order of magnitude. I'd say maybe closer to 2 orders.

[secessus]

> Short term cooling as a benefit to washing an array is small enough to be pretty much non existent and can be ignored.

That's my original point: naive observers on YT and elsewhere can be misled by transient effects.

[nwdiver]

If cleaning them has that little effect I will stick to just hosing them off.

Unless you have really good water I wouldn't even bother with that. Overtime you're gonna get mineral deposits. At a minimum rinse them when it's cool to avoid thermal shock.

[J.P.M.]

I am sure glad to hear that. I am surprised at how dirty my panels have gotten here in a week. I've been shopping for a squeegee with a long handle.

If cleaning them has that little effect I will stick to just hosing them off.

I'd hose the array off in the A.M. before 0800 hrs. or before and take stock of any changes in production. Maybe do it a couple of days in a row.

If things have not been cleaned for a long time, a scrubbing with a soft brush may be in order. I use Dawn dish soap. Home Depot/Big Box has long handled brushes. Mine has a 4 section handle w/ ~ 16-18 ft reach. The brush is 18" wide. Mine gets a lot of use and has lasted 5 yrs. It might be reaching the end of its service life. I only use it because I hose/brush/hose my array ~ 120 times/yr. in ~ 2 month periods for fouling and performance measurements. Long, boring story. The rest of the year the array simply gets hosed ~ 1X/month if it doesn't rain. Simple hosing restores ~ 2/3 to 3/4 of the performance lost from fouling. The array fouls at an approx./average rate under normal weather conditions such that a performance penalty of ~ 0.75 %/week is about what I can expect.

FWIW, after a lot of measuring/cleaning/measuring before/after performance a lot of times about 5 yrs. ago when I started this quest, I couldn't measure/see a benefit to squeegeing. One conclusion I've reached is that the human eye is a poor tool to use when judging the effect of water spots on an array. It might look like crap, but I've never been able to measure a significant difference in cleaning effectiveness between cleaned and squeegeed, and cleaned and a simple drip dry.

There's a lot of difference in how fast /slow and what type of fouling accumulates on an array. I wouldn't be surprised if other arrays near my area or in areas similar to mine foul in similar ways and at similar rates. But if you live, for example, next to and downwind of an interstate, your fouling patterns and cleaning requirements will most likely be different than mine.

[PNW_Steve]

I live in a dusty semi-rural area. I cleaned my panels once, only noticed a nominal increase in production. Within a week or so my panels were dirty again. I have't bothered with cleaning again.I believe this was discussed in an earlier thread and the general consensus was that cleaning panels is not necessary unless they are REALLY dirty to the point where they are completely obstructed from sunlight.

I am sure glad to hear that. I am surprised at how dirty my panels have gotten here in a week. I've been shopping for a squeegee with a long handle.

If cleaning them has that little effect I will stick to just hosing them off.

[J.P.M.]

Just a thought, at lower temps the increase in panel efficiency might be directly related
to the increase in operating voltage? Then only MPPT systems would be able to take
advantage of the additional output. Need a temp-efficiency chart. Bruce Roe

As you know, panel operating voltage is mostly f(cell temp.). As cell temps. go up, voltages across panels go down pretty much inversely proportional to cell temp. w/the constant of proportionality being the panels' published temp. coeff. of voltage. That's what the textbooks and theory all say and, more importantly, to me anyway, that's what I've measured and confirmed on my own. Details on request.

What I'm trying to explain here and what I believe or at least thought we're talking about here is why the short duration and probably small temp. decreases in array temp. seen from from a water spray on an array will have a trivial to no measurable effect on the short term much less the daylong output of a PV array. The voltage drop will be maybe a couple % for maybe 10 minutes for most panels and spraying conditions.

That's also what happens to my array every time I hose it down - which has happened about 120 times/year in identical fashion at the same time of day for the last 6 years. I stopped keeping track of the voltage drop and how long it lasts from spraying ~ 20 gal. over 16 panels after about 100 or so observations. That's were my estimates of voltage drop and duration came from.

Respectfully,

[bcroe]

Just a thought, at lower temps the increase in panel efficiency might be directly related
to the increase in operating voltage? Then only MPPT systems would be able to take
advantage of the additional output. Need a temp-efficiency chart. Bruce Roe

[J.P.M.]

because they are temporarily force-cooled by the cleaning solution, yes.

No. Probably not.

In spite of what you may think, such temperature reduction effects from sensible and evaporative cooling resulting from spraying water on an array will not have a measurable effect on array output.

For several reasons and as f(several factors), such cooling will last only for a matter of a few minutes (for example only, maybe about 3 to 10 minutes or so for my array, depending mostly on wind vector, dew point and air/water temp. diff.), and in addition, such spraying/washing better be done early or very late in the day at a time when irradiance on the panels will be quite low, making power output at such times quite low to begin with. So, very short term temp. reduction at a time of not much production in the first place is a double whammy for making it a very small effect in output.

Bottom line: Short term cooling as a benefit to washing an array is small enough to be pretty much non existent and can be ignored.

[J.P.M.]

There were some websites (can't find them now) one was from Australia and the other in the US, where solar enthusiasts/installers took dozens of different panels from different manufacturers and placed them in near identical real world installations and monitored the results over time. The result was that there was little difference between the major manufacturers. Of course some panels performed better than others, but it was not a significant amount. Similar technology, similar results.

I agree with you that focusing on the actual installation and choice of installer is time well spent vs. panel manufacturer. I feel I may have made a mistake not getting micro-inverters vs. string w/ optimizers. If I want to add more panels in the future I will have to upgrade my inverter. I didn't think about that at the time. I expect to have a excess of 2,500 - 3,000kWh at the end of my first year true-up. My wife wants to get a EV in the near future and I'm not sure if we will generate enough to 100% cover our current usage + the EV.

Some closer sources, like poster Solarix, have done that or something quite similar. Not writing/speaking for him, but he's done some side by side stuff that seems to show string inverters perform quite well compared to micros or optimizers.

[secessus]

Are you writing that you believe cleaner panels have improved performance because they are running cooler ?

because they are temporarily force-cooled by the cleaning solution, yes.

[PugPower]

There were some websites (can't find them now) one was from Australia and the other in the US, where solar enthusiasts/installers took dozens of different panels from different manufacturers and placed them in near identical real world installations and monitored the results over time. The result was that there was little difference between the major manufacturers. Of course some panels performed better than others, but it was not a significant amount. Similar technology, similar results.

I agree with you that focusing on the actual installation and choice of installer is time well spent vs. panel manufacturer. I feel I may have made a mistake not getting micro-inverters vs. string w/ optimizers. If I want to add more panels in the future I will have to upgrade my inverter. I didn't think about that at the time. I expect to have a excess of 2,500 - 3,000kWh at the end of my first year true-up. My wife wants to get a EV in the near future and I'm not sure if we will generate enough to 100% cover our current usage + the EV.

[J.P.M.]

On June 12, 2020 I generated 45.192kWh. It was probably my 2nd day best since the array was installed in Oct. 2019. After looking at your data, I have to agree. There really is little real world difference when comparing similar wattage panels from the most common manufacturers: LG. Panasonic, Sunpower, etc. People paying more for advertised claims of more low-light power or specs showing fractions of a percentage of better efficiency are wasting their money. I have never known this as a definite, but have always assumed it.

Thank you for the information.

More Q.E.D. FWIW:

06/12/2020:
Your system: 45.192 kWh/6.7 STC kW = 6.75 kWh/day per installed STC kW.
Same day my system: 34.67 kWh/5.230 STC kW = 6.63 kWh/day per installed STC kW.
Given my stuff is ~ 5+ yrs. older, seems like output on that day per in stalled STC kW was about equal. Also, that data seems to add reinforcement to the idea that for mostly equator facing stuff, small variations in orientation don't matter a whole lot of difference in output.

From what I had learned over the years, the inference/claims of higher output through "highest efficiency" and such stuff - particularly Sunpower's hype - looked like B.S. to me.
So, while I had always planned to get PV, if for no other reason than something to provide more unprocessed data to fuel my curiosity, the S.P. choice, while still good equipment that has not failed once after going on 7 years, was made toward seeing if the S.P. claims of "highest efficiency" etc. had any validity.

Short conclusion: They to not. My conclusion is that S.P. stuff simply costs more but is no more fit for purpose in terms of annual output and reliability than other stuff that costs less.
Folks would be better off saving money on less overpriced equipment of about equal quality and maybe spending more time evaluating vendors. Their systems overall quality and construction - which is where problems usually originate in the first place - would benefit in terms of workmanship and professionalism.

To be clear: S.P. stuff is high quality and it does meet the output expectations their spec sheets will allow one to calculate.

But, "most efficient" ? No f-bombing way. Good quality ? - yup.

Overpriced with respect to quality, annual output and reliability compared to other stuff that costs less ? Fur sure.

Used to be S.P. systems cost ~ 20-25 % more for the same annual output and reliability compared to other decent but not high end stuff. That % premium/gouge seems to be coming down a bit for the last year or two but not enough. It also seems S.P. system reliability has taken a hit, particularly since their foray into micro inverters. I wonder if the Maxeon spinoff.
Also, their product support, which never was that good, now sucks worse.

I live in an HOA that has ~ 140 PV installations in the hills behind the Welk resort - you probably know where it is. Anyway, I do the project review/approval recommendations for the HOA for residential PV. Also, about a dozen or so PV owning neighbors allow me to monitor their systems output. All that has been an education in itself and pretty much provides further confirmation of my conclusions about high priced PV systems as well as a lot of other things.

That people are paying for advertising claims is, to my way of looking at it, a bit wide of the mark. A good part of the success of the S.P. yarn seems to be due to the solar ignorance of their marks (customers). I wrote some stuff for our community newspaper/blurb several years ago about some things to perhaps look out for in the way of scams and B.S. when looking for ways to reduce their electric bills - mostly to point out the value of conservation first and also how to spot B.S. from solar peddlers. I wasn't surprised at the vituperation and rancor from the usual suspects: old, entitled white guys whose conversations are often or usually more useful as ranting edicts than sources of useful information. However, I was a bit (but not too )surprised at how much of it came from owners of S.P. systems who drank the S.P. koolaid.

[PugPower]

On June 12, 2020 I generated 45.192kWh. It was probably my 2nd day best since the array was installed in Oct. 2019. After looking at your data, I have to agree. There really is little real world difference when comparing similar wattage panels from the most common manufacturers: LG. Panasonic, Sunpower, etc. People paying more for advertised claims of more low-light power or specs showing fractions of a percentage of better efficiency are wasting their money. I have never known this as a definite, but have always assumed it.