How much electricity will my solar panels lose if they get dirty? The answer from experts is, “where do you live.” The amount of loss can vary greatly even between locations that are only a few miles apart.
The amount of power lost every day due to buildup of pollutants, such as smokestacks, exhaust systems, jet aircraft exhaust, animal farms, wind, rain, dusty agricultural areas, areas adjacent to salt water, freeway exhaust, or dust varies with every location. Properties adjacent to cement plants, gravel plants, landscaping nurseries etc. are examples where your location is more likely to be affected by dirt and debris.
While the percentages vary among locations, monitoring can determine the actual amount of power lost each day.
Remember in the previous article I mentioned that dirt and debris buildup is cumulative. The amount of loss can range from a few percent to 50 % or more. Understand that solar panel manufacturers try to avoid the subject, as they do not want to make potential buyers aware of the problem. Since the use life of a solar system is 20 to 25 years, think how the car windows on your car would look if you only hose it off every six months.
Does rain help? Yes, a little. However, having lived in Seattle for many years I can tell you with absolute certainty that rain will not clean windows. It can help, but it will not clean.
Rain can also create problems. Dirt and debris must be swept off of the solar panel. Improperly directed spray patterns can cause and debris to accumulate on the side of a panel. This runs the risk of reverse polarity occurring in a solar panel. As noted in a previous article, reverse polarity will eliminate any production from the solar panel and drag down production in other panels in the same string. It can also create a hot spot, which has the potential to kill a solar panel.