man showing you how to clean solar panels

How to Clean Solar Panels

Carlos

Written by qualified solar engineer Carlos on January 6, 2019

Using a soft brush with distilled water and dish soap is sufficient to clean your solar panels. However, there are different ways to clean them and various tips that should be used during the process. In this article you will learn some valuable tips that will make the cleaning process even easier for you.

Soiling on solar panels related to debris, dust, bird droppings, or dirt can accumulate on the surface of the module and lead up to 30 % annual losses in worst cases.

Typical annual losses attributed to this factor are located between 2% and 5% regularly, however, by accumulating soiling on the PV system, losses can increase over time. That is why it is important to know how often or when to clean your solar panels.

Tips Before Cleaning

Turn Off the PV System

The first step that you need to think of before cleaning your solar panels is to turn off the DC switch located in the combiner box. This is essential to guarantee your safety and to make sure that the solar panels won’t get damaged by water inside the junction box, exposed wires, or broken seals while DC electricity is flowing through the system.

New PV systems in the US according to NEC 2017 are now required to have a rapid shutdown system, that will instantly reduce the voltage of the PV array to zero from an easy access location inside the house or business. This will guarantee security in any case for the homeowners and firefighters as well.

Always remember to push that red button in the rapid shutdown box before going to clean your solar panels.

Use a Soft Brush or a Sponge

When cleaning solar panels it is essential to use the right cleaning equipment. The glass is strong but using abrasive materials can scratch the surface of the glass, reducing its performance or even damaging the module.

If your solar panels are installed on the ground, then you can opt to use a simple sponge to clean them up or a soft brush as well. However, if they are located on the roof, then you must use a soft brush coupled with a long extension to make the work easier and safer from the ground.

soft brush for cleaning solar panels

Avoid Using Water with High Mineral Content

Module manufacturers recommend the use of distilled or de-ionized water to clean solar panels. Mineral-rich water may leave deposits of particles over time and its chemistry is not recommended for the glass of modules.

If you do not have access to de-ionized or distilled water, you can use a water-softening hose attachment to filter those minerals.

Do Not Use High Pressure

Using high pressure to clean the solar panels can force water to enter into the junction box or plugs that are not 100% sealed. As a general approach, it is recommended that when using a hose, pressure stays below 40bar.

It is also recommended that the water jet cleaning creates a sheet of water spray at the nozzle in order to reduce the pressure received by the glass.

low pressure water cleaning solar panels

Source: Polywater

Use Water With a Similar Temperature

Solar panel manufacturers do not recommend the use of cold or hot water to clean the panels. The reason behind this is that sudden and drastic differences in temperature could crack the surface of the glass.

It is best to clean your solar panels using ambient temperature water during early mornings (6-7 am), when the modules’ temperatures will be low after cooling down overnight and when the solar generation has not started.

Never Use an Abrasive Material to Clean the Solar Panels

Sometimes, homeowners or salespersons may advise you to use detergents to clean the modules. However, all that you truly need is the dish washing soap and water to clean them.

Using laundry detergents designed for other purposes is not recommended because they can create moisture or delamination at solar cell level which will void the warranty of the panels and will inevitably damage them.

Read Your Solar Panel Manufacturer Instructions

No one gives advice on how to properly clean and treat your solar panels like the manufacturer. Installation manuals of modules are generally available on the internet and many come included with your panels. Take a look at them and learn more about your modules.

Do Not Ever Walk Over the Modules

Solar panels are designed to withstand specific distributed snow and wind loads. If your concentrated weight is above the designed loads then you could cause micro-cracking, declining the performance of the module over time. Besides, the solar panels’ surface can be slippery, and if you are adding soap and water to the mix, the probabilities of falling are quite high. As long as you are careful, the chances of solar panels being dangerous are low.

image showing how not to stand on the solar panels when cleaning them

Source: JinkoSolar Installation Manual

The Simple Process

Gathering all of these tips let’s take a look at a review of the steps you need to follow:

  1. Start early in the morning.
  2. Disconnect your PV array from the inverter by pushing the rapid shutdown button or pulling down the DC disconnect switch in your combiner box.
  3. Gather some distilled water and mix it with a little dish soap (just a little).
  4. Look for a soft brush and start cleaning your modules with the water mix.
  5. After all modules are soaped, remove the soap with a low-pressure hose.
  6. Leave the modules to dry over 30-45 minutes and turn back on the DC disconnect switch.

Other interesting solutions mainly designed for roof-mounted systems are the solar panel cleaning products like Polywater. They use specially designed chemicals for module cleaning that allow you to perform the maintenance from a safe distance on the ground or using stairs. Moreover, these products are designed with a specific water pressure that does not harm the surface of the glass. Polywater also uses a hose attachment bottle with the mix of water and soap with the option to rinse (using the mix) or to wash (only using water).

As you can see it is a simple process that, when carried out with a routine schedule, can maximize your solar energy outputs over the year.

Never forget that maintenance procedure is a two person job and that also involves checking your wires, possible signs of degradations, delamination, damages, or burns behind the solar panels (if possible).

Solar panel manufacturers never recommend to go up to the roof to clean your modules without special protection (harnesses), but with these tips, you can do it yourself while being on the ground or using movable stairs.

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6 Comments

    1. Carlos

      Hi Nadeem,

      So, the usual practice for cooling down the module is convection, meaning using wind and leaving a space behind the module during installation to allow the air to cool it. Ground mount systems have much better cooling system than roof arrays because of obvious reasons.

      The ideal normal operation temperature of the modules is generally located between 45-60°C. If the temperature is higher, it doesn’t mean its wrong or that the module is damaged, it is mainly due to higher ambient temperatures.Operating at a much higher temperature, can indeed reduce the performance of your modules, sometimes from 100% to 70%of what they should be producing. If your location is very hot, it is always recommended to go with modules that have a lower temperature coefficient, the best ones in this case in the industry are the HIT Panasonic modules.

      Now if you want to cool down your panels with spray water, it is possible. In some cases, and especially in arid regions that lack enough rainwater throughout the year, using water has become a common practice to maintain good performance in the modules. However, here you must know several things:

      – It must be “spray water” meaning non-pressurized water. That does not include the water irrigation system of your garden (in case its ground mount) non a high pressure hose water that you shoot from ground to the panels in the roof.
      – The water temperature must NEVER be cold, putting cold water into a hot panel can crack the glass and damage it badly. Recommended water temperature is around 25-30°C.
      – The ideal moment when you want to cool down your panels with water is when they have an operating temperature of 45°C. How to know this? Well, you can setup a temperature sensor that lets you know when this temperature is reached, of course, it will not be something that you want to do every time, especially if you do it manually.
      – You must know that just a couple sprays on some sections of the module a couple of times a week will do little to no improve in performance. It is actually expected that for every minute that water flows through the panels, temperature will reduce between 1.5-3°C. That is if you do this in 6 intervals of 5 minutes waiting 15 min between each cooling process during a couple of hours using an average flow water rate of 20lts/min and during the hottest hours of the day (11-1pm for instance), you can actually expect a very good improve in performance everyday.

      As you can see, using water for cooling the modules, is indeed a very a good approach, however, doing it regularly, for the time required, and effectively enough as to represent an important positive impact in your PV system output, involves more than just using spray water from a bottle. Systems implemented in very dusty and hot regions like the Middle East generally need a controlled water cooling system that does this on a regular basis and the recycles the hot water that comes from the panels mixing it with cold water in large water tanks installed below ground to avoid solar radiation from heating the water.

      This of course is a much complicated process, but its the right way to cool down your panels with water.

      In a few words, water is good for cooling, but using spray water manually, not constantly, in the amounts needed, and not for the enough time, may be just a waste of your time.

      Hope that clarifies your question

  1. Avatar

    Actually we always use water spray to cool solar panel and now it has covered with water stains and we use detergents to remove this stain but now no result has been shown by the detergents and now the panel are covered by white yellow layer….plz suggest me how we can get rid of such stains….

    1. Carlos

      Hello dear Nadeem

      interesting problem that you have here,

      So first thing that you must know, is that you must not continue using laundry detergents to clean your panels, this will cause further issues in the visuals and the performance of your modules. Simply use dish soap or even better choose polywater cleaning. You can check further info about it here https://ecotality.com/solar-panel-cleaning-equipment-and-tools/.

      Second, if your solar panel has turned yellow, and that is, that the solar panel now has a slightly yellow look that can be seen inside the glass, then it means that you have an issue with the ethy vynil acetate (EVA) layer of the module. The EVA layer is the encapsulant, also known as the backsheet of the modules. Basically two films of this layers “sandwhich” the solar cells for protection.

      Basically what happens when the module turns yellow is that an uncontrolled chemical reaction (involving the materials used in the glass, the EVA layer and silicon) occurs inside the EVA layer releasing the formation of acetic acid which eventually gives the module a yellow look, and in worst cases, a brown aspect. This can either happen at cell level, meaning looking like a stain in just an area of the module, or at the whole panel.

      There can be up to three reasons for that, one is simple degradation, this can happen in modules with over 20-25 years old, especially those from the older solar industry. The second one is using a low quality solar panel that uses a low quality EVA layer, this could happen in the first years of using the panels, and if so, you should talk with your installer about it. The third one is water entering inside the water seal of the module when using high water pressure, this one can also lead to corrosion of the cells and leakage currents that drastically reduce the performance of the module. Whatever the reason for this yellow look on your module, I’m sorry to inform you that sadly it cannot be fixed.

      The efficiency or performance of the yellow panel reduces between 9-50% as time passes by due to the creation of hot spots or increase in temperature due to this internal chemical reaction.

      The best I can tell you is try to detect if it is an internal issue of the panel, or if it looks like an external source of soiling that may have got stuck in the glass, this can be known easily if when the touching the panel in the yellow side, there is a rougher surface than in nearby areas. If so, try to use the polywater cleaner and rinse it carefully, if its external it should improve, if its internal, there’s no much to do about it. If you are still on product warranty, contact your installer or solar panel manufacturer.

      Hope this may help you and good luck

  2. Avatar

    I have a question. I had my house painted. Painter was to roll paint so I did not cover solar panels. Well he sprayed and now I have paint on my panels. How can I get the paint off with out damaging the panels? What is the best way to remove the paint from inner panels that are difficult to get at?

    1. Carlos

      Hello Janice,

      I’m sorry to hear that Janice. So, solar panels have an anti-reflective and hydrophobic coating in the glass, so the last thing that you want to do is to scratch them or use any strange or out of pocket chemical that somebody tells you, even if it works to remove the paint, it will probably damage the glass surface and will also void the panels warranty.

      The best thing you can do is take a look at your warranty terms and solar panel manual to see their limitations and recommendations. In general, it is recommended to use dishwashing soap to do the cleaning, if you haven’t do that yet, that might be a good starting point. You can also use Polywater and Winsol products listed in this page to do the cleaning. These are specialized chemicals that are specifically intended to clean the glass surface without damaging the glass surface. You can also get one of the cleaning kits (that you still need anyways) to have a better chance to remove the paint with a soft brush.

      With those tools you may be able to get the paint off, if you don’t, then you may need to charge the painter for that.

      Hope that helps and good luck

      Best
      Carlos

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