Jun 012014
 

When someone gets a new rooftop solar installation, the second question they always ask is “how often do I need to clean my solar panels.” We’ll answer that question on today’s show — taking into account the different effects of rain, dust and electric rates (BTW, the first question people always ask is “how do I read my electric bill;” but that’s a topic for another show).

Rooftop solar panels get dirty primarily from wind-blown dust and pollen. Birds are usually not a problem unless your last name is Hitchcock and you live in Bodega Bay. As panels get dirtier, their output declines. A small amount of soiling — say a light dusty film — may only cause a 5 percent output decline. However, when panels get very dirty — perhaps in an agricultural area or location that does not get regular rainfall — the output decline can be greater than 20 percent. A good heavy rainstorm will usually wash away most of the accumulated soiling.