Solar Panel Cleaning

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.