The brush extends to 75", but since the panels are on a 2nd story roof, I can only reach the first 8 panels without creeping near the edge of the roof. I ended up zip tying the brush to an extension pole we used for painting, and I was easily able to reach to the end of the 2nd row of panels. At 6AM this morning, I climbed up on the roof with the brush, the pole and the hose and washed away. In 15 minutes, I was done as well as I could be. The brush is very soft and there still seemed to be some dirt I wasn't able to scrub away, but it is a lot cleaner. Today will be cloudless and mild, like yesterday and the day before, so I'll be able to make a good comparison on the effects of the cleaning. So far, at 9AM, the panels are producing 2245 W and total power produced is 3.033 kWH. Compared to yesterday at 9AM, the panels were delivering 1965 W and had produced 2.574 kWH. Instantaneous output has gone up 14% and total production is up 17%. Pretty good! We'll see where the day's production ends up, and I'll post updates for below. It certainly looks like I'll be making periodic trips onto the roof to wash the panels.
Update: At the end of the day, 24.5 kWH of electricity were produced versus 21.99 kWH yesterday, an 11.4% increase. That's pretty significant. It's as if I added 2 more solar panels to the 16 we already have. The question is, when should I get back up there and clean them again? One interesting bit from the above table is that dirty panels are actually less productive in the morning and evening. In other words, the grime on the panels obstructs more sunlight when the sun is not directly above them. I'm sure there's some high school physics explanation behind that, but I'll let someone else figure it out :)