I’m having my windows professionally cleaned in a couple of months. I do this every few years as the spiders nests build up and there can be quite a bit of dust. The same provider also can clean my solar panels.
In the past I cleaned my solar panels when they weren’t really very dirty. Fortunately, now PG&E offers data download in a cleaner format than in years past. I can download a little over a years data in a giant comma separated file, which is compatible with Excel or Numbers.
By simply looking at the electrical usage for a few days during the same period year to year, I can compare the kWh generated. I choose a few afternoons from 2-5pm, where very little electricity is being used. This April has been cooler and cloudier than normal, so I focused on three days I knew were sunny in 2014. The data is broken down into simple 15 minute intervals as shown below.
By doing some very simple sums over three periods on the same days in 2013 and 2014, I actually generated more power in 2014. So I have really no reason to clean the solar panels this year.