Does Anyone Recommend Solar Panel Cleaning When Installing?

[Gavin A]

Let me know what the results are with that install. It will be interesting. Most commercial installs with a low angle are losing between 15%-20% generation after 2-3 years if they have not been cleaned at all.

This is the bit I'd dispute, and you've not shown any evidence to support it.

It's dependent on the atmospherics, but one low angle commercial install was losing a lot more than that, around 40%. We now clean it twice a year.

I've no doubt that some low angled installations in particularly dusty environments will suffer significant reductions in output as you suggest, and benefit from more regular panel cleaning, but I really can't agree that this is the norm.

Your first case study refers to an array on an arable farm next to a grain dryer towards the end of harvest time, where the panels were obviously extremely dusty, so the immediate benefits are fairly obvious. I'd expect the situation would have been very different had the cleaning taken place a month after the harvesting ended, once a few heavy rain storms had passed, but yes that would be the sort of situation where I'd expect panels may well benefit from more regular cleaning.

Checking through your site, you probably offer a decent service for these sorts of sites, but let yourself down by talking complete rubbish about the extent of the issue, eg.

"Engineers also found that at a few sites, photovoltaic panels were dirty enough to warrant cleaning due to very specific and localized circumstances. For example, being directly next to and downwind of a highway, factory or agricultural field may generate enough dirt to warrant cleaning."

This must represent 90% of all solar panels mounted in the UK.

What possible justification could you have for taking a very reasonable statement about a few sites being found where panels were dirty enough to warrant cleaning due to specific environmental factors, then twisting this to claim that this must represent 90% of all solar panels in the UK?

You quote data from a study conducted in San Diego in a drought, and even give the differences in monthly rainfall levels between San Diego and London prior to completely ignoring the impact of rainfall levels, using stupid claims about rain not actually cleaning panels.

It is the RAIN here which puts dirt on the panels, it does not clean them.

utter bull.

Your site basically contains a couple of interesting case studies, but intersperses these with misleading rubbish, and I for one won't have any dealings with companies who spread such disinformation about our industry. It's a shame you've chosen this approach as there is a need for decent companies to clean the minority of systems that would benefit from cleaning due to environmental factors that result in them getting particularly dirty.

consider me not impressed.

 

[Solar Steve]

I wondered about getting mine cleaned this year. Not because I think they are prone to getting very dirty, but they are at an aprox 30 degree angle so may not self clean as efficiently as those at a steeper angle.

I have noticed a drop over the last couple of months compared with last years output, but then winter output is frankly pish poor anyway on my install and way under estimate due to surrounding trees.

I think I'll wait and see what the March to May output is compared with last year...

I'm very, very confident that if you were to have your panels cleaned, you would see an increase in generation. The best time of year to do this is April or May.

 

[Solar Steve]

Are there any known incidents of moss or algae type organic stuff covering solar panels? From what I vaguely remember lots of roofs in the UK have a moss type covering.

Moss can easily grow in the join between the bottom edge of the panel where it meets the framework. We come across it frequently.
Algae will grow on any glass surface if left uncleaned long enough. Check out the windscreen on a car that has been dumped in someone's garden for 5 years. Glass on solar panels will age in the same way.

 

[Solar Steve]

The flaw I can see in those comparisons, is that you'll get variation from day to day anyway, due to varying sunlight (obviously!!! )

Showing, say 3 months, averages before and after would give a more accurate picture.

Hi Andy. If you read the article closely, you will see that we have taken into account the difference on light levels on different days. We have tried many ways to work out how to measure the increase, including the one you mention, but it proves difficult to provide a close % in increase. The day before, the day after on arrays mounted next to each other remains the most accurate way that we have found.

If anyone can work out a more accurate way, I am open to suggestions. We will consider all options seriously.

 

[Solar Steve]

Yes, but it's not a bad demonstration. You've got two 'control' installations in the same location for comparison. Quite impressive really, although I guess a farm throwing crop dust into the air is a pretty dirty environment for solar panels.

Thanks Andy. It's the most accurate way we have found of making a comparison and the beauty of the research is that it was the farmer who tested his arrays, not us.

 

[Solar Steve]

Check out here for 'independant' analysis:
Official Blog: Should you spring clean your solar panels?
and:
Cleaning solar panels often not worth the cost, engineers find

W've just stripped off and re-installed a small system we installed in Jan 2011, to install some solar thermal alongside it, Urban Area, 38°, due south, and because of how little dirt there was on them we didn't bother to go to the (small) effort of washing them...The dirt on them was negligible.

On some other sites (20°) in heavy urban areas we've seen significant dirt build up and cleaning has had a positive effect, on another site at 10° elevation they were very very dirty after only six months. So as per the google analysis, location and angle of elevation are significant factors, -

Angle of elevation seems to be the most prevailing factor, but not the only one.
This article discusses the differences between the San Diego findings and the UK: Solar Panel Cleaners | Clean Solar Solutions Ltd | San Diego Solar Panel Cleaning Research - How Does It Compare To The UK?

 

[Solar Steve]

This is the bit I'd dispute, and you've not shown any evidence to support it.

I've no doubt that some low angled installations in particularly dusty environments will suffer significant reductions in output as you suggest, and benefit from more regular panel cleaning, but I really can't agree that this is the norm.

Your first case study refers to an array on an arable farm next to a grain dryer towards the end of harvest time, where the panels were obviously extremely dusty, so the immediate benefits are fairly obvious. I'd expect the situation would have been very different had the cleaning taken place a month after the harvesting ended, once a few heavy rain storms had passed, but yes that would be the sort of situation where I'd expect panels may well benefit from more regular cleaning.

Checking through your site, you probably offer a decent service for these sorts of sites, but let yourself down by talking complete rubbish about the extent of the issue, eg.

What possible justification could you have for taking a very reasonable statement about a few sites being found where panels were dirty enough to warrant cleaning due to specific environmental factors, then twisting this to claim that this must represent 90% of all solar panels in the UK?

You quote data from a study conducted in San Diego in a drought, and even give the differences in monthly rainfall levels between San Diego and London prior to completely ignoring the impact of rainfall levels, using stupid claims about rain not actually cleaning panels.


utter bull.

Your site basically contains a couple of interesting case studies, but intersperses these with misleading rubbish, and I for one won't have any dealings with companies who spread such disinformation about our industry. It's a shame you've chosen this approach as there is a need for decent companies to clean the minority of systems that would benefit from cleaning due to environmental factors that result in them getting particularly dirty.

consider me not impressed.

Hi Gavin. Sorry this has caused you such consternation. I will try to address each of your points as you have highlighted them to me.

This array is mounted at more of a normal angle than the grain dryer and has a sprinkler system installed which is used weekly and was cleaned well after harvest and had been exposed to the heavy rain storms that you imply would have cleaned them: Solar Panel Cleaners | Clean Solar Solutions Ltd | Solar Panel Cleaning Completed On Largest Solar Array In Shropshire
He asked us to clean his solar panels as a test case to see if manual cleaning gave him any increased generation as well as using his sprinkler system. He is a very astute man and made it more than clear to us that if there was no benefit, he would not allow us to darken his doorstep again! He did his sums and compared the increase in generation after our cleaning, compared with the cost of his cleaning. He was amazed how much money he was losing. Within 1 week he contacted us and booked a second clean on his Shropshire array and booked us for a clean on his Powys array: Solar Panel Cleaners | Clean Solar Solutions Ltd | Solar Panel Cleaning Completed On One Of The UK's Largest Solar Farm's Of Its Kind This year, he has already booked us in and confirmed dates for not 2, but 3 cleans of each of his arrays in April, June and August. As I say, he is astute, a number cruncher. He owns Shropshire's largest array and what was the largest in Powys too. The number crunchers always use us again because they see we bring value and it works out financially profitable for them to have their panels cleaned.

We do not talk rubbish about the extent of the issue. EVERY farm site we visit results in at least a 20% increase from our cleaning if the panels are on the roof for 12 months or longer.

Regarding the San Diego 90% figure, I was not suggesting that 90% of arrays in the UK need cleaning due to specific circumstances. I was saying that 90% of the arrays in the UK are mounted next to a road, factory or field. They will all inherently need cleaning. The roadsides due to traffic film, the factories due to airborne industrial pollution and the ones in fields due to the dust from harvest, and general farm life.

Regarding my statement that rain gets panels dirty being 'utter bull' as you so eloquently put it, this is a true, provable statement. EVERY outdoor surface deteriorates due to being exposed to rainwater. Rainwater is not a cleansing agent, it contain airborne pollutants. That's why after a shower, the raindroplets that were left on your car windscreen dry spotty. We are working with professors at the CSER centre at St. Asaph which will be looking at the effect of, among other things, rainwater and how it leaves a film on solar panels. This will be done at a microscopic level and we will be carrying out the cleaning to see what benefits that brings down to a microscopic level. The research on this has already started and I'm afraid I will not accept your 'utter bull' statement when university-standard research has begun to prove me correct. We are also helping the BRE centre in St. Austell with some similar research. If you will not accept my findings, perhaps you will accept thiers when the results are published.

You are right. We do have some interesting case studies, all of which were carried out from April last year onwards. Every site that we clean we attempt to carry out a case study for regarding the data and output increases. We will continue to do so and build client confidence in what is a new and exciting industry for the UK. We do not 'spread...disinformation about our industry'.

Myself and my company are at the very forefront of solar panel cleaning in the UK in many different ways other than physically cleaning the panels. Research is one of those avenues. Some of the largest solar installation companies now consult us with the planning of future arrays with a view to cleaning etc.
I may be new to this forum, but I'm not new to solar panel cleaning. I have spent nearly 7 researching this field in Germany and the U.S. before we really took the cleaning service to town here. I don't need to trick anyone. I have done my homework and know the field better than most in the UK.

 

[Marvo]

Okay I have almost zero PV knowledge but I have a couple of theories that I've managed to spawn from my ignorance none the less.

I can understand the fact that if a PV panel is mounted at a steeper angle then it would be more effectively cleaned by rain because the velocity of water across it will be faster and carry particulates away more effectively but how much benefit this extra cleaning has may be offset by the angle that the sunlight hits the panel. If the light hits the panel at 90degrees which I imagine would be the most efficient angle then the effect of any dust and debris coating the glass would be less than if the light meets the panel at say 40 degrees. Taking this completely unsubstantiated theory one step further it's possible that cleaning the panels may show less efficiency increase in summer when the sun has a higher arc across the sky than in winter when the suns arc is much lower and the angle of incidence on the glass would be shallower.

 

[Gavin A]

Hi Gavin. Sorry this has caused you such consternation.

Feel free to amend the offending sections of your website.

This array is mounted at more of a normal angle than the grain dryer and has a sprinkler system installed which is used weekly and was cleaned well after harvest and had been exposed to the heavy rain storms that you imply would have cleaned them

Maybe. But as stated, I don't have an issue with the idea that installations in high dust environments would need cleaning, I have a problem with your generalising from this to statements such as this.

Most commercial installs with a low angle are losing between 15%-20% generation after 2-3 years if they have not been cleaned at all.

EVERY farm site we visit results in at least a 20% increase from our cleaning if the panels are on the roof for 12 months or longer.

What I suspect is the problem here is that you're suffering from selection bias, in that you will pretty much only be getting called out to systems that are underperforming and dirty, then generalising from your experience and concluding that because most of the systems you see are underperforming by 15-20% due to dirt, that this means that most commercial systems will also be underperforming by that sort of level.

If you've genuinely carried out a random survey of commercial systems, then fair enough, but I assume not seeing as you've not referenced it, and your statements seems to be at odds with several installers experiences on here.

Regarding the San Diego 90% figure, I was not suggesting that 90% of arrays in the UK need cleaning due to specific circumstances. I was saying that 90% of the arrays in the UK are mounted next to a road, factory or field. They will all inherently need cleaning. The roadsides due to traffic film, the factories due to airborne industrial pollution and the ones in fields due to the dust from harvest, and general farm life.

it's a US report, therefore highway would refer to a motorway or particularly busy A road, and in terms of fields, it's only really arable fields that produce significant levels of dust. So no, 90% of UK buildings wouldn't be affected in this way, nothing like it.

Interesting contradiction in that paragraph btw, sentence 1 you're not suggesting that 90% of arrays need cleaning due to specific circumstances, sentence 2 you state that 90% of arrays in the UK are mounted in those circumstances and will all inherently need cleaning.

Regarding my statement that rain gets panels dirty being 'utter bull' as you so eloquently put it, this is a true, provable statement. EVERY outdoor surface deteriorates due to being exposed to rainwater. Rainwater is not a cleansing agent, it contain airborne pollutants. That's why after a shower, the raindroplets that were left on your car windscreen dry spotty.

Rain isn't a 100% perfect cleaning agent, but the cleaning impact of rain in the UK far outweighs the impact of dirt deposited by evaporating rain, so overall rain acts to clean the panels - cleaning from rain is the major reason that steeper panels need cleaning less than panels at a shallower angle.

The panels in the san diego test therefore will get a dirtier quicker than panels in the UK (on average) due to the higher levels of air borne dust, and lack of rainfall for most of the year, rather than vice versa

We are working with professors at the CSER centre at St. Asaph which will be looking at the effect of, among other things, rainwater and how it leaves a film on solar panels. This will be done at a microscopic level and we will be carrying out the cleaning to see what benefits that brings down to a microscopic level. The research on this has already started and I'm afraid I will not accept your 'utter bull' statement when university-standard research has begun to prove me correct. We are also helping the BRE centre in St. Austell with some similar research. If you will not accept my findings, perhaps you will accept thiers when the results are published.

ask them a simple question - are panels likely to be dirtier after a dusty dry spell, or after a period of heavy rainfall? Rainfall will eventually leave a film on panels, but this has a minute impact relative to all the airborne dirt the rain washes away.

We do not 'spread...disinformation about our industry'.

what's this then?

A good way to illustrate why rainwater will not clean solar panels is by looking at your car windscreen. If you didn't clean your windscreen for 6 months, how much visibility would you lose? If left, the grime on your windscreen would accumulate and eventually 'green' over. Even if the car is rained on, the rain contains airborne dust particles that settle and attach to the surface after the rainwater evaporates. When we use our windscreen wipers, we clean the centre of the screen, but where the wipers do not reach, there is a film of dirt. The whole of your solar panel is in exactly the same condition as the edge of your car windscreen because they are both exposed to the same elements.

To my knowledge, none of my customers are in the habit of driving their panels long distances attached to the front of a vehicle moving at high speed in a position where they will get regularly sprayed with dirt and salt laden spray kicked up from wet roads by the vehicles in front of them

 

[Gavin A]

I'd also note the way you reference the google report on the impact of cleaning their panels, but fail to mention that this only applies to the panels that they had mounted almost horizontally on carports, and don't seem to quote this rather telling paragraph about their roof mounted solar panels.

The rooftop solar panels are a different story. Our data indicates that rain does a sufficient job of cleaning the tilted solar panels. Some dirt does accumulate in the corners, but the resulting reduction in energy output is fairly small — and cleaning tilted panels does not significantly increase their energy production. So for now, we'll let Mother Nature take care of cleaning our rooftop panels.

Official Blog: Should you spring clean your solar panels?

I see from the comments on that article that you disagree with google's findings on that, but yet you feel happy enough to quote their findings on the impact on their flat panels. Why do you find one part of their report credible, but ignore the other part of the report? Do you have some reason to suspect that google lied about their experience?

Most panels may eventually end up dirty enough to warrant cleaning, but IMO very few would be bad enough to warrant cleaning as often as every 6 months as your site appears to recommend, or anything close to it.

 

[SolarCity]

We keep data on every single one of our installs. Not one of them has experienced a noticeable drop in yield. I don't keep data on how many of them actually clean their panels but I'm assuming that the vast majority of our customers do not.

I have to admit I was amazed to see that state that those panels got to in your example but I think we can all see that that is an exceptional case. I've never seen panels in that kind of state before. It is clear that panels in those circumstances will definitely benefit from the cleaning.

I'm yet to be convinced that the vast majority of installs will need much washing if ever.

 

[Solar Steve]

Hi Marvo. Panels mounted at a steeper angle stay cleaner, longer than those on a shallow angle. But they still benefit from periodic cleaning. Some need cleaning more than others based on location. Cleaning should take place during the spring and summer months when the daylight hours are longer and the panels will produce to their max.

 

[Solar Steve]

Feel free to amend the offending sections of your website.

Maybe. But as stated, I don't have an issue with the idea that installations in high dust environments would need cleaning, I have a problem with your generalising from this to statements such as this.



What I suspect is the problem here is that you're suffering from selection bias, in that you will pretty much only be getting called out to systems that are underperforming and dirty, then generalising from your experience and concluding that because most of the systems you see are underperforming by 15-20% due to dirt, that this means that most commercial systems will also be underperforming by that sort of level.

If you've genuinely carried out a random survey of commercial systems, then fair enough, but I assume not seeing as you've not referenced it, and your statements seems to be at odds with several installers experiences on here.


it's a US report, therefore highway would refer to a motorway or particularly busy A road, and in terms of fields, it's only really arable fields that produce significant levels of dust. So no, 90% of UK buildings wouldn't be affected in this way, nothing like it.

Interesting contradiction in that paragraph btw, sentence 1 you're not suggesting that 90% of arrays need cleaning due to specific circumstances, sentence 2 you state that 90% of arrays in the UK are mounted in those circumstances and will all inherently need cleaning.


Rain isn't a 100% perfect cleaning agent, but the cleaning impact of rain in the UK far outweighs the impact of dirt deposited by evaporating rain, so overall rain acts to clean the panels - cleaning from rain is the major reason that steeper panels need cleaning less than panels at a shallower angle.

The panels in the san diego test therefore will get a dirtier quicker than panels in the UK (on average) due to the higher levels of air borne dust, and lack of rainfall for most of the year, rather than vice versa


ask them a simple question - are panels likely to be dirtier after a dusty dry spell, or after a period of heavy rainfall? Rainfall will eventually leave a film on panels, but this has a minute impact relative to all the airborne dirt the rain washes away.


what's this then?

To my knowledge, none of my customers are in the habit of driving their panels long distances attached to the front of a vehicle moving at high speed in a position where they will get regularly sprayed with dirt and salt laden spray kicked up from wet roads by the vehicles in front of them

We can only base our statements on the data we have accumulated to date. If the data changes, our statements will change.

Rain rinses panels, we clean panels. There is a difference. You would not put dirty clothes in the washing machine on a rinse cycle and expect them to come out clean. Something more intensive is needed.

Panels don't need to be driven around to accumulate dirt anymore than a car windscreen does. Next time you see a car on someone's front lawn that has sat there 12 months, see how dirty the windscreen is. If possible, sit inside the car and try to see out. Then you will be like the cells inside a panel. You'll notice the windscreen is not letting in the amount it should. Therefore the panel will not be letting in the light it should and will not produce to its maximum potential, thereby losing the owner money.

Think about it. If a panel owner is hoping to get his ROI after 10 years, but his panels are producing 10% less than they should! it will take him an extra year to get his money back. The larger the array, the greater the financial loss.

 

[Solar Steve]

We keep data on every single one of our installs. Not one of them has experienced a noticeable drop in yield. I don't keep data on how many of them actually clean their panels but I'm assuming that the vast majority of our customers do not.

I have to admit I was amazed to see that state that those panels got to in your example but I think we can all see that that is an exceptional case. I've never seen panels in that kind of state before. It is clear that panels in those circumstances will definitely benefit from the cleaning.

I'm yet to be convinced that the vast majority of installs will need much washing if ever.

it depends what you class as noticeable though I suppose.

Those panels are not the exceptional case on farms, they are the norm. Go through other case study articles on farms and you'll see.

i would expect you to be convinced about cleaning yet because it is such a new industry for the UK. It has been around in other countries for a long time though and is here to stay. That's why I researched foreign markets before I set up the business, to see if there would be a demand or not. Based on the money we are making from this, happily I'd say there is.

 

[JD6400]

I will add my two penneth in as somebody that will more than likely be using Steve's services on several reasonable sized roof mounted arrays on both dairy and arable farms , and depending on the service given and the benefits received I will then be looking at introducing him to a 1MW ground mount system which we were heavily involved with last year .

Although I am a little sceptical as are others as to the severity of system losses wholesale and the frequency of cleans needed as claimed , I am also of the opinion that generally only clients with a problem will be the lions share of his contracts . I also know for a fact that some systems out there do need this service , either through poor system design or just through being installed in more aggressive environment than would normally be preferred .

Gavin has a very good point when it comes to the trial on the Lincolnshire grain store ( not one of mine ) and as I type this now , I am looking across the fields at it and I can assure you that it is in an environment that I would definitely class as aggressive . Now I am reasonably confident that we had not received much in the way of rain around here from the end of harvest up to the time of this clean , so although it is a good comparison with the other systems , I am sorry Steve but I think a few more comparisons of the same systems should be included through out the year .

That said I do not doubt it would have significantly benefited from that clean , as in my experience of grain dryer sites , just about all surfaces get covered in a fine dust that turns to a stubborn slime when an average rain fall accurs . And as for dairy farms that feed a TMR I would venture to say that you will have a job to clear that stuff perfectly even with a manual clean !

It would appear at the moment ( through personal correspondence ) that he is providing a reasonably priced service , that I will be using and will be more than happy to report back in this thread about !