A solar panel typically consists of solar cells covered by a protective glass coating, and just like your car windshield – the longer it's outside – the more likely it will get dirty and need to be cleaned.
Pollution, traffic dust, leaves and even bird droppings contribute to preventing sunlight from reaching the solar cells in your solar panels.
The more dirt – the lower amount of electricity they will produce. While many factors affect how much electricity your solar panels will produce – dirty solar panels can be one of the biggest, and easiest to fix.
Experts agree that dirty solar panels don't produce as much power as clean panels. That loss may range as high as 25% in some areas according to the National Renewable Energy laboratory. Individual dealers have reported losses as high as 30% for some customers who failed to ever clean their panels.