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The Dirty Solar Panel Experiment

Solar Panel

Perfect Testing Conditions

The solar system is two years old and the panels have never been cleaned. The rain water has done a good job of washing away dirt accumulation. We are in rural Texas and the building has a low slope roof (2:12) and has missed every rain shower for the last two months. We are  surrounded by ongoing construction projects, and the heavy equipment generates a significant amount of dust and dirt. Consequently, the solar panels have become quite filthy.

Experiment Setup

For this experiment, we used an isolated row of 12 SunPower 335-watt solar panels with SolarEdge DC Optimizers. The DC optimizers allowed us to measure variations in power and energy output from the solar panels.

Experiment Process

  1. Record Solar Panel Production Before Cleaning: Each solar panel has a slightly different power output. Premium solar panel manufacturers guarantee a Positive Power Tolerance, meaning every solar panel performs at or above an advertised value. Recording the power and energy data before cleaning helps us identify the impact of dirt on each individual panel. 
  2. Clean the Solar Panels: We cleaned every other solar panel to serve as a control. Most manufacturers recommend using water and a soft rag for cleaning. Avoid using chemicals, pressure washers, or abrasive materials. 
  3. Record Solar Panel Production After Cleaning: We used the dirty panels as a reference to find a time interval with similar sunlight conditions.

Results – Power and Energy Improvement from Cleaning

Power Improvement

Clean solar panels showed a 2-3% increase in power output compared to dirty panels. Power output data is useful but represents only a single moment in time.

Energy Improvement

Clean solar panels yielded an average 3.5% higher energy output. This table displays the daily energy yield differences between dirty and clean solar panels:

Energy Improvement


Cleaning dirty solar panels results in a minor production boost, averaging around 3.5%. While this shows some improvement, it suggests that the overall impact of dirt on solar panel performance is relatively small. Soiling is already accounted for in design calculations for solar production, and regular rainfall can help maintain panel cleanliness to a degree. Therefore, the necessity for frequent manual cleaning may not be as critical as often perceived.

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