Dirty versus Clean Solar Panels

We normally do not clean our solar panels, but after a few months in places with a lot of dust and very little rain was the panels covered with dirt. When looking at the panels would the dirt be assumed to limit the output a lot.

From the picture above is this panel looking like some cells are almost covered completely. This is caused by the solar panels mounted flat and when it rains is the dirt collecting on the lowest spot. With 2 days with a clear sky can we compare output from one day to another. So the washing with a small pressure washer can start.

After the cleaning is the output measured and compared on the graph below.

As the panels get cooled from the water is the output for a short time increasing even further but after 15 minutes has the temperature settled and the output is not 7.9% higher (measured on the average of 10 minutes). So washing is not generating a lot of extra energy even with panels being very dirty.

The pressure wash required 9.2 gallons of water and used 93 Wh of electricity.

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