I have a monitoring system that constantly collects data on how much the PV system produces every hour and instant production. One thing that I keep monitoring is what is the peak amount of wattage does the system produce. I deduced that the closer we approach the summer solstice the more power the PV system would producre. General that is true, I have seen a constant increase in monthly production since the winter solstice.
But what I did notice is that for a couple of days after a rain storm the PV system was generating more power then on average. To the tune of 2 kilowatts (or about 5%) more. Two day after the rain storm the production would drop back to the lower average peak output.
The pattern was very constant (see chart below). Rain and then a couple of higher peek production days and then a return to the lower peeks. So I deduced that the days following a rain storm the air is cleaner, less smog. anyone can see, as they fly in the the Los Angelse basin, that most of the time there is thick layer of smog. So the smog is filtering the sun light and less sun is reaching the PV panels.
So you might argue hat the rain cleans off the PV panels. All the rain washes of the dust awasy and the panels receive more sunlight and therefore producer more power. Sounds reasonable, BUT just recently we has a service clean the PV panels and both the day of the cleaning and the two day after the cleaning the power production was the average peek not the 2 kilowatts higher peek. Both day were also very sunny and cloud free.
So the more I look at the monitor reports, the more I’am convinced that the smog is costing me about 2 kilowatts a day in lower power production. All due to the SMOG levels in our area.