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  • Writer's pictureJeff Mathias

Cleaning Your Solar Modules

Updated: Feb 15

I am often asked, "What is the customer's responsibility for maintaining a solar system to protect this 25-plus year investment? The answer is to check the inverters or performance monitoring to ensure your system is running, and to clean your modules, usually annually..

When I return to sights many years after installation, without fail, the number one issue affecting system performance is dirty moduless. We clean our floors, cars, and even our pets, but the moduless on our roof, or in our yards are neglected. How much does cleaning really effect performance? Some studies show up to 25% improvement after cleaning (I think this is high but a 7-15% improvement is likely).

On Fathers Day, my eldest son Chaz offered to clean my solar panels. I try to clean my panels really well in April or May, when solar production starts to increase and always before June 1st, when Peak Summer rates begin with PG&E. I also hose them off 3-4 times through summer and fall, as needed, before the rains. This year, the business of life led me to put off this cleaning. So on Father's Day, as I sipped my coffee in the back yard, Chaz was up on the roof cleaning my panels. We do not use any soap (which can leave a soap scum), just plain water (I attached a spa filter to the hose to eliminate particles) and a little elbow grease, or in this case Chaz's elbow grease. We use an extendable RV brush with a hose attachment, which works well for us and our roof (see above).

In this picture you can see my panels were not filthy, they just had dust and pollen accumulation since the last rains. And you can also see the difference a little scrubbing and water does.

To the left is a picture of a panel from one of my customer visits, showing a typical year's worth of soiling. Look at the lower edge of the module and how the dirt is building up from the winter rains on the lower edge. This dirt will expand into the cell area, "shading"the modules. These lower edges should be scrubbed to remove this build-up.

And then there are those sites, that even though their systems are in the middle of a field, are clean as a whistle when I show up. These customers seem to take a personal pride in maximizing the production of there systems.

Okay, back to my system. So Chaz is still up on the roof cleaning my modules, and I must say he does a better job of it then I do. He scrubs off the edges, and the pollen which can be tough. And he does all this with a smile

They say the proof is in the pudding. Chaz cleaned my panels in the early morning, 8:30 am, before the panels heated up (hot glass and cool water can cause cracking). Here is my performance monitoring data, which makes it handy to see the changes cleaning makes. Before cleaning, the highest daily reading I was getting was 45 KW, with an average of about 42 KW.

In the week after cleaning, I had 4 days exceed 49 KW. Throw out the one June day we had rain, 6/22/12 (rain in June?), and the average was over 46 KW. That's over a 10% improvement. Thanks Chaz!

If you would rather have someone else clean your modules (It was so nice to watch it being done vs doing it!), we recommend Pro Solar Clean, or by phone 707-971-0017 or Pura Vida Solar Cleaning, or by phone - 707-376-8432.

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