Solar Panel Cleaning

This article goes over the basics and importance of cleaning solar panels for both residential and commercial solar PV systems

When it comes to keeping your solar panels clean, the most asked questions are why, how, and how often? 

Why keep solar panels clean?

The first question can be answered in a fairly straightforward manner: to improve energy output.  Like shading, dirt and other things blocking your solar panels from the sun can drastically reduce your energy output.  As for the numbers, the Solar Electric Power Association (SEPA) states that energy output can be decreased by about 10% due to dirt and other residues.  In areas with more bird dropping, pollution, or dust, the efficiency can decrease as high as 15-20%.  So in order to get the energy output that you paid for, cleaning is needed every now and then. 

How do I clean?

As for how to clean a solar panel there are two main ways.  First you could get a self-cleaning system that works by using a low volume nozzle to spray water and soap onto the solar panels and wipes them clean like a windshield wiper.  These systems can be used for the solar panels that either cannot be cleaned safely or the benefits outweigh the costs of the system.  In the near future, instead of using an automated soap and water system, solar panels could be cleaned using an electrostatic charge that moves dust to the edges of the panel.  While it has been tested on Mars rovers, it has yet to hit the solar system market. 

The other way is to just clean them manually.  There are some factors to think about before you take some soap and hose your solar panels down. 

  1. If you are thinking about the convenience factor, just a simple hose of the solar panels should get them clean enough to improve efficiency. 
  2. If cleaning the solar panels require more than a hose (like for bird droppings and such), manually cleaning the solar panels with a brush and water may be needed.
    1. It is recommended to use NO soap and soft water where possible. Hard water (with a high mineral content) can eventually build up heavy deposits.
    2. Never try to climb out onto the array - use a soft brush with an extension pole. Boat cleaning brushes (around $30) are the best since they offer flow-through handles which deliver water right to the bristles and are designed not to scratch.
    3. If chemical cleaning is required, use a detergent that will not damage aluminum. Many domestic detergents can damage panel frames and clamps.
    4. For larger arrays, a commercial window cleaning system is advised. These brushes can extend up to 30' and will deliver deionized water directly to the glass surface to remove dirt and leave no deposits. Commercial system can cost up to $600, but can pay for themselves quickly by keeping large arrays clean.

How often should I clean?

The last part is answered in two parts: one for tilted solar panels and one for flat solar panels. 

Tilted solar panels are able to benefit from Mother Nature’s natural cleaning due to the rain being able to get most of the dirt and grime off.  Even though there might be some dirt collecting at the corner of the solar panel, the effect on the output is insignificant compared to the time you would have to spend cleaning it off.

As for flat solar panels, even though there is a clear benefit for cleaning the solar panels, you have to do a time vs. benefit analysis to determine how often they should be cleaned.  For areas that collect dirt easily on the solar panels, some wash around every other month.  For areas with less dirt, it is recommended to wash them around 1-2 times a year.   

Even though there is no official set times to wash your solar panels, cleaning them is definitely beneficial towards improving your energy output.

Comments

Even with moderate cleaning of panels, the gallons of water per MWhr of power production with PV is a fraction of the water required for other forms of power generation.

Nuclear Power   400-750 gal/MWhr
Coal                    300-400 gal/MWhr
Natural Gas        100-300 gal/MWhr
Hydroelectric      1400 gal/MWhr
Solar Thermal     1600 gal/MWhr
PV                         30 gal/MWhr


One advantage to using an Enphase system is that you can monitor the output of each panel individually.  I've been cleaning a single panel on the array while letting the rest accumulate dust and dirt, then watching the power production to see just how much of a difference it makes.

Currently the clean panel is running about 1% higher output than the dirty panels.  When that difference climbs to 2% or so I'll go up on the roof and clean the entire array.

Thanks for the handy tip on using aluminum-safe detergents!

 

Good tips,this blog is very educative and have answered almost all the questions I had in mind about environment,thanks for the good work.

 

Sheds

How much PV can be put in 1 arce?

The question is a bit off topic but a rough estimate is about 250Kw/acre...

250kW per acre is a very fair estimate for crystilline silicon (xSi).   That being said there are many factors that play into this number.  Here are a few of the key factors that will help determine the peak kW dc you can fit into an acre of land.

  1. Location - Where will the system be installed.   Different latitudes require different tilts thus have varried effects on shading.  This will enable a higher or lower ground coverage ratios (GCR is the percentage of the area you can cover with panels vs. needing to leave open)
  2. Mounting - Type of mounting will also effect shading and thus GCR
  3. Type of PV - poly / mono crystilline silicon vs. thin film - each of these technologies have different efficiencies thus you can achieve higher peak watts dc per acre


Thanks for sharing good valuable information,which can help people Solar Panel Cleaning , solar photovoltaic panel right information, latest news and mostly all needs of human being we can get here.
 

A couple of points about automatic systems:

  1. These are essentially irrigation systems. Anyone who has had a sprinkler system knows that they require maintenance. The idea that no one will have to go on the roof once the wash system is installed has no basis in fact. And for safety, it's better to have a pro wash team on the roof with fall protection than to have a maintenance guy up there tinkering on sprinkler heads...
  2. A wash system can can't do a good job over time. The spray pattern won't get all the dirt, resulting in hard, built-up shading spots that cause high electrical resistance. 
  3. Having a wash system on the roof gives the false impression that nothing has to be done to it for maintenance. A PV system is a machine (a very simple machine) and it needs at least an anual inspection above and beyond the monitoring software. An anual wash is a great time to inspect the system.
  4. Water + Dirt = Weeds. I've seen actual plants growing in the dirt that collects around sprinked modules. Vaguely humourous but ultimately not what is intended by the term "green power".

I'd love to see a Roomba robot that crawls over the array to clean it, but until then I think manual cleaning is the way to go.

In response to the above comments on automatic systems.  I have a Heliotex System on my roof and it performs beautifully and my panels are spotless everyday.  Sure there are some irrigation components in these systems, but I did a lot of research before I bought.  These guys know what they're doing.  The proof was in my increase in output after the installation.

Heliotex has a lot of high profile commercial and government installations and have been working with major panel manufacturers for years now and have an effective refined product.  I highly recommend the system and their service is awesome!

If you decide to manually clean your panels as I did in the beginning, you will have a perpetual obligation to climb on your roof risking injury and roofing material damage.  I tried to keep up with cleaning my panels and the automatic system was a no-brainer, not to mention I'm not getting any younger...