Google has a 1.6 MW solar panel installation in California.
The research they carried out concluded clearly that dirty solar panels will have a negative impact on their performance. After their solar panel array was installed 15 months, they experimented with solar panel cleaning. After the first session of solar panel cleaning, their output doubled on some solar panels. Eight months later, they had their second session of solar panel cleaning and the solar panel efficiency increased again by 32%. After having solar panel cleaning, all of Google’s solar panels increased their output by at least 12%.