Google has the answer on how dirt affects the efficiency of solar panels. While it takes a study, it doesn't take a genius to figure that anything covering a solar panel immediately reduces its efficiency for it to harvest light. Google facilitated a study that would back this belief up with data. The study began by comparing the two different sets of solar panels in Google campus - the flat ones in carports and the tilted ones on roofs.

Google published parts of the study online entitled "Getting the most out of Google's solar panels."