I had been doing a better job in the past on cleaning our solar panels last years and I got a bit lazy this year. That was stupid, they had a layer for dust pigeon poop, and other crap.|
It took an hour with water hoses, a broom, and dishwasher liquid, but the effort was worth it.
I only have a week's worth of data and it's weather dependent, but the peak production number averaged over a week went from 4542 Watts to 4964 Watts, and the daily production went from 30.3Kwh/day to 34.9Kwh/day.
That may have been 300Kwh to 500Kwh that have been lost due to dirty panels.
Moral of the story: don't be lazy :)