Cleaning solar panels

[Robert1234]

My last comment on this subject, then I'll be done too....Do I believe in washing solar panels? Absolutely, but at what cost?

Like our friend Volusiano in AZ, we all need to determine our own value/return with regards to our solar cleaning. Using the UC-Davis study, no washing with little-to-no rain fall resulted in a 7% power inhibition after six months (if I remember that correctly). Assuming linear deposition, that's an average power loss of 3.5% over a six month period. Also assuming a small system like I have that generates 22 kwh per day and a value of electricity of $0.12 per kwh, that's a monetary lost value of about $17. IF I could find someone to wash my panels for $17 every six months, I would only break even. That's why I do it myself. The only factor that would get me to pay someone else to do that job is if my panels were on my roof cause I don't like heights. (Since I have a ground array, that's not an issue.)

This whole discussion about the quality of water you use versus standard tap water is just simply silly. The use of purified water has essentially zero value less than a week after the cleaning process, and even then it probably only adds a very minute fraction of a percentage in power improvement at Time=0 (the very first day after cleaning) if it can really even be statistically measured at all. Thus my view that this thread delving into the value of RO technology to produce 0 TDS water is a moot discussion of marketing hype and hocus pocus. Would be much more valuable if people would focus on a cleaner that might somehow add anti soil deposition properties without interfering with light transmission. That might have some value and is where I was hoping to lead this thread. I'm sure it's out there (and if not I'll make you one ). Oh well....

The value of washing solar panels can easily be understood. Keeping the homeowner off the roof is a worthy endevor. I just wish the people making $$ from it would do so without taking unnecessary advantage of people. It needs to be sold for what it is and sold at the right price to be a sustainable business. Whether it's a good business or not at that point is the business owners call.

P.S. For what it's worth.. diluted standard household ammonia (or windex) is a great panel cleaner. Zero residue. Just be sure to rinse the aluminum frames well to prevent any possibility of NH4OH corrosion. As a plus... the chemical that is washed off and ends up on the ground is converted to fertilizer and feeds the plants. Can't get any "greener" than that now can you . (Pun intended)

[Volusiano]

This whole discussion about the quality of water you use versus standard tap water is just simply silly.

There are many different aspects of solar panel cleaning. I believe the original question from the OP is not about whether it's worth the ROI to clean solar panels. The original question from the OP is how the solar panels are cleaned.

So I think the discussion that ensued about how they're cleaned, whether it be by using water-fed-pole technique with pure zero TDS water to leave wet and let it dry cleanly, or by getting up on the roof and cleaning them the traditional way with tap water, wetting and drying with a squeegee manually, is very relevant to the original question and topic of discussion at hand.

Whether the cost of using pure water water-fed pole technique to clean solar panels is justified or not is another thing. I think it's relevant enough and worthy of discussion here as well. But to dismiss the discussion of pure water water-fed-pole cleaning vs tap water traditional squeegee cleaning as being silly is missing the point.

It's not that pure water does a better job compared to tap water. That's not the argument here. The only reason to resort to pure water is to enable the use of a water-fed pole to do the cleaning from afar in a safer position, since you're not going to be able to squeegee the panels dry with this approach. Because safety is a VERY important aspect of solar panel cleaning, I think the discussion of using water-fed pole cleaning for safety reason (and ease of use as well) has merit and is very relevant to the topic at hand. Just as relevant as the question on ROI for solar panel cleaning.

[bcroe]

Saftey

Because safety is a VERY important aspect of solar panel cleaning, I think the discussion of using water-fed pole cleaning for safety reason (and ease of use as well) has merit and is very relevant to the topic at hand. Just as relevant as the question on ROI for solar panel cleaning.

Is the safety related to climbing on a roof, or manually putting water on something that
might be running at 400 VDC?

So much wet stuff falls here, no need to wash panels. My snow pole is long
and made from insulating materials. Bruce Roe

[Volusiano]

Is the safety related to climbing on a roof, or manually putting water on something that might be running at 400 VDC?

Both actually. Normally you'd disconnect before you clean as a precaution, but there's no telling what the risk can be because if the sun is out even when you make a point to clean early in the morning or late evening, the panels can still be energized somewhat and water may find its way to cause conduction somehow at the panels before the main disconnect. So there's definitely an advantage to do water-fed pole cleaning from the perspective that you're standing far away at the end of the dry pole and you don't get wet, as opposed to be on the roof up close and personal drying to hand squeegee the wet panels dry.

[Mike90250]

one more time for late arrivals.
I use DI water from a MR Clean car wash kit to rinse my panels. If you use hard water, the mineral spots become permanent, and not good for solar harvest.

[russ]

The reply from Rainx - Thanks to them for replying.

Russ

Hello Russ,

Thank you for contacting ITW Global Brands! To answer your question below, the Rain-X Glass Treatment is fine on glass. The question has been raised whether it will affect the performance of solar panels. We do not have any data or experience with solar panels, so we cannot say whether it affects performance. We have seen occasions where treated optics, often with a polymer coating, were negatively affected by Rain-X, so we advise against its application on treated optical glass. This may have been the idea behind our Consumer Inquiry representative's response.

While we have not seen any visible difference in the refraction of light through treated glass vs. untreated glass on vehicle windshields, in theory the refractive index may change slightly. We have never seen an effect significant for driving visibility.

Based on our experience we would expect improved performance due to glass remaining cleaner with less soil and mineral deposits to block light. However, we do not have any data to make that claim and would be interested to hear the results from experts on solar panels. Our background and business is automotive and household consumer products, so we have not actively pursued the solar panel market. Again, we urge caution if there are any surfaces other than ordinary glass used in this application.

Please let us know if there is something else that we can help you with, and we would be happy to assist you.

Sincerely,
ITW Global Brands
Office of Consumer Services

[inetdog]

The reply from Rainx - Thanks to them for replying.

Russ

Thanks Russ!

Now we can all argue about what that means rather than speculating about what they will say.
A definite step forward!

[Volusiano]

Now we can all argue about what that means rather than speculating about what they will say.

I guess this means that I won't be putting RainX on my solar panels anytime soon, LOL.

[inetdog]

I guess this means that I won't be putting RainX on my solar panels anytime soon, LOL.

If you have panels which are inexpensive enough that they do not include anti-reflection coatings, all you need to worry about is compatibility with the panel seals, which may use materials not common on cars.....

You could just try taping off the edges of the panels before applying, I suppose.

The new super-hydrophobic compound currently for sale at Big Orange is interesting too but it is a relatively thick coating which would be far more likely to cause problems.

[russ]

Thanks Russ!

Now we can all argue about what that means rather than speculating about what they will say.
A definite step forward!

Right! All one can safely do is not use the material.

[solarrevolve]

Solar panels are basically self cleaning. The best time to clean solar panels is after the rains end. You can clean them using perfect tools, allowing you to stay on the ground, like a good quality soft brush and a cloth covered sponge on the other coupled with a long extension. You should not try to clean your rooftop panels cleaning your panels from the ground if it is not possible.

[Ian S]

You should not try to clean your rooftop panels cleaning your panels from the ground if it is not possible.

That doesn't apply to those of us who have flat roofs and can't even see the array from the ground.

[+3 Golfer]

After reading this entire thread and having lived with a 3.36 kW and a 4.96 kW system with a tilt of about 22* in the Valley of the Sun (Phoenix area), I thought I'd share my experiences with cleaning solar panels. We get very little rain in the Valley but generally get several periods a year where it might rain 0.5 to 2.0 inches over a 12 - 24 hour period. The air is extremely dusty as moderate winds pick up desert dust plus we get several dust storms (Haboobs) each year.

A neighbor and friend that lived a street away had the identical 3.36 kW system. He never cleaned his panels and I cleaned mine when they had a noticeable covering of dust. Thus, I cleaned about every 6 - 10 weeks. I monitored our daily outputs via the Sunny portal for 2 1/2 years until I moved. Immediately after cleaning my panels, I saw between about a 1/2% to 1% jump in my output over his uncleaned panels. But within about 2-4 weeks after cleaning, our outputs were virtually the same again. This repeated itself after every cleaning. Our monthly and annual outputs were always within 1% of each others. On 6400 kWh of annual production, that's about 64 kWh maximum of additional generation that I saw from cleaning vs not cleaning. IMO, it certainly would not make sense to pay someone to clean solar panels for less than $10 savings a year.

I do not have a comparable for my 4.96 kW system that I can monitor. I have cleaned the panels IIRC 4 times in about 2 years (usually after a Haboob has gone through). I can only compare my output before and after the cleanings for similar days and find the same as with my smaller system which is no more than a 1 % loss from "dirty" panels even after 4-6 months of not cleaning. On 9000 kWh of annual production, the 1 % amounts to 90 kWh and because of the rate schedule I'm on (3 hour peak 2-5 pm M-F) will only results in about $8 since I can control water heating and pool pump load to end up with net zero on-peak for each month.

For those that want to clean, I purchased a 16' telescoping (3 poles) aluminum pole and an 18" squeegee and soft cloth covered scrubber to attach to the pole for IIRC less than $30 in total at either Lowes or Homedepot. The squeegee and scrubber attached to a small wood pole doubles as a great window cleaner. I use tap water either via a garden hose or pressure washer and have noticed no residue buildup on the panel or window glass for the time I've been cleaning. Since I had/have single story homes with tiled sloped roof, I clean via a ladder from the ground (2 rows of panels). If there's a corner of a panel that is difficult to squeegee (would have to move the ladder to get a better angle to squeegee), I drape a terry cloth towel over the squeegee to sop up excess water in the corners.

Also, I did not notice a steady linear decline in output as panels become "dirtier" (which I thought I might see as a function of time). I would have thought that since my neighbor never cleaned his panels that after 3-4 months of no appreciable rain, I'd see a 2-3% difference in output after cleaning my panels over his but I didn't. As I said above, it seems that my panels and his panels would reach a certain level of decline then level off. This may be due to the dirt being very fine particles (like dust on furniture) and perhaps some gets blown off during windy conditions (which may not be the case in other climates) and the layer of dust on the panels remains about the same.

Bottom line: As every installer I've talked to in the Phoenix area says, cleaning in not needed. Cleaning from normal rainfall will suffice. I've proved this to myself with my own systems. (But I probably will still clean after Haboobs)

[russ]

Here - when weather conditions are just right and there is a sand storm in Egypt we can get a muddy rain - that could cut output a bit!

[J.P.M.]

After reading this entire thread and having lived with a 3.36 kW and a 4.96 kW system with a tilt of about 22* in the Valley of the Sun (Phoenix area), I thought I'd share my experiences with cleaning solar panels. We get very little rain in the Valley but generally get several periods a year where it might rain 0.5 to 2.0 inches over a 12 - 24 hour period. The air is extremely dusty as moderate winds pick up desert dust plus we get several dust storms (Haboobs) each year.

A neighbor and friend that lived a street away had the identical 3.36 kW system. He never cleaned his panels and I cleaned mine when they had a noticeable covering of dust. Thus, I cleaned about every 6 - 10 weeks. I monitored our daily outputs via the Sunny portal for 2 1/2 years until I moved. Immediately after cleaning my panels, I saw between about a 1/2% to 1% jump in my output over his uncleaned panels. But within about 2-4 weeks after cleaning, our outputs were virtually the same again. This repeated itself after every cleaning. Our monthly and annual outputs were always within 1% of each others. On 6400 kWh of annual production, that's about 64 kWh maximum of additional generation that I saw from cleaning vs not cleaning. IMO, it certainly would not make sense to pay someone to clean solar panels for less than $10 savings a year.

I do not have a comparable for my 4.96 kW system that I can monitor. I have cleaned the panels IIRC 4 times in about 2 years (usually after a Haboob has gone through). I can only compare my output before and after the cleanings for similar days and find the same as with my smaller system which is no more than a 1 % loss from "dirty" panels even after 4-6 months of not cleaning. On 9000 kWh of annual production, the 1 % amounts to 90 kWh and because of the rate schedule I'm on (3 hour peak 2-5 pm M-F) will only results in about $8 since I can control water heating and pool pump load to end up with net zero on-peak for each month.

For those that want to clean, I purchased a 16' telescoping (3 poles) aluminum pole and an 18" squeegee and soft cloth covered scrubber to attach to the pole for IIRC less than $30 in total at either Lowes or Homedepot. The squeegee and scrubber attached to a small wood pole doubles as a great window cleaner. I use tap water either via a garden hose or pressure washer and have noticed no residue buildup on the panel or window glass for the time I've been cleaning. Since I had/have single story homes, I clean via a ladder from the ground (2 rows of panels). If there's a corner of a panel that is difficult to squeegee (would have to move the ladder to get a better angle to squeegee), I drape a terry cloth towel over the squeegee to sop up excess water in the corners.

Also, I did not notice a steady linear decline in output as panels become "dirtier" (which I thought I might see as a function of time). I would have thought that since my neighbor never cleaned his panels that after 3-4 months of no appreciable rain, I'd see a 2-3% difference in output after cleaning my panels over his but I didn't. As I said above, it seems that my panels and his panels would reach a certain level of decline then level off. This may be due to the dirt being very fine particles (like dust on furniture) and perhaps some gets blown off during windy conditions (which may not be the case in other climates) and the layer of dust on the panels remains about the same.

Bottom line: As every installer I've talked to in the Phoenix area says, cleaning in not needed. Cleaning from normal rainfall will suffice. I've proved this to myself with my own systems. (But I probably will still clean after Haboobs)

Thank you for the input. FWIW, seems well reasoned and reasonable to me at least.

While keeping in mind that different local climate conditions, array orientation and very local topography can and usually will govern the rate and type of panel fouling (dirt) that an array will experience, perhaps part of the reason I think the above is well reasoned is because I've found pretty much the same fouling rates and nonlinearity. From OCT./2013 install to Jan./2014 1st cleaning, no rain during the intervening period that I could measure, my est. fouling was of the order of ~~ 1% using 2 consecutive, nearly identical solar days for comparison, 1st one dirty, 2d one cleaned early A.M. Irradiance and climatic variables monitored w/Davis pro 2 w/ solar irr. mon. Recent cleaning Apr./2014 about 6 weeks after rain, and some spotty showers and again using consec., nearly identical insolation days, showed something less than 1% fouling as best est.

Also, as an experiment, I've attempted to measure the decrease in transmission of a glass plate positioned next to the array in the same orientation. The glass is mounted in a plastic sleeve such that one side is completely sheltered from the environment as is one half of the other ("top") side, the other half of that ("top") side is thus always exposed to the environment and assumed to be seeing conditions identical to the array, but never touched and never cleaned. About every 2 weeks or so, depending on sun conditions, I remove the glass plate from its fixture and place the glass over the weather station solar sensor in the horizontal position 12 min. before and 12 min. after solar noon, on the assumption that on a clear day, horizontal solar irradiance will be symmetrical about solar noon - the first 12 min. for the exposed (dirty) part of the glass, then rotate the glass 180 deg. about the vertical axis and measure trans. through the (assumed) clean portion of the glass, I.E., the 2d 12 min. for the (assumed) control part. The weather station measures and records conditions including solar irradiance at 1 min. intervals. So far, after about 6 months of this, I think I'm seeing a decrease in transmission that appears asymptotic in nature. That is, the rate of transmission decrease is sort of linear initially and after about 4-6 weeks or so levels off to something like .99-.98 of its original (clean) level.

To repeat, these are local results and for a short period. I'm sharing for what they are worth. To repeat, I'd guess every array will see different rates as f(climate, orientation, local topography, other) and results of any measurements will probably also be f(dirt size, type, sensor wavelength response, other). However, I'd also guess that the rate of fouling may in general tend to be more asymptotic than linear in some fashion depending on a boatload of conditions that are not only not measured but probably not known, thought of, or well understood. I think it may be interesting to note that desert conditions as the poster describes and somewhat less severe conditions at my location seem to produce, at least to my reading, similar results, at least anecdotally.