How is it best done?
I have a Very tall, 2 story roof, the low part of the eves are about 22' from the ground. I've tried a sidewalk sweeper type hose nozzle, but it does not even begin to reach high enough to get to the panels on the roof. I suppose I'll have to climb up there and do it by hand with a car wash brush? Soap to use? Soap to avoid? Rinse agent to use? car wash/wax? Final rinse with DI water ? I figure I'll have to do this about every three months - I am a block downwind from a 10 lane freeway, and get lots of road dirt blowing on to them, they aren't blue any more, they are dirt brown.
Mike

Let us know how you do it.

One installer included 25 annual washings in the installation price, but in my case, I'll be doing it myself.

How about a 6HP Pressure Washer (Costco), 0-degree long-reach nozzle, and a low-wind day?

That could at least provide some artificial rain. If you have to scrub oil or soot off the panels, you're in for a climb. I'm not going up there. This is the tallest 2story house I've ever seen, and the roof tiles are curved, and I'd probably break something..

I get on the roof with hose, bucket, pole brush and dish hand soap ... been doing it this way for 5 years without issues. takes anout an hour to do all the arrays

I've done it 2x now, 1st time I was all prepared with a pole brush, soap etc.. and had a friend man the hose bib for me. I ended up just using the hi-pressure sweeper nozzle and blasting each panel clean, only moving slightly form my central point.
2nd time was just the hose and sweeper nozzle

next time, I'll try some "spot free" rinse agent, maybe

Windex makes a product for unreachable windows. It's a plastic bottle pf cleaning solution that goes on the end of a hose. You flip it to "soap", squirt the suds out, then flip it back to "rinse" and rinse off.

Anybody know any reason why that wouldn't work? It doesn't do a bad job on my windows.

i think mike has a bigger problem than just using the hose with or without windex for i believe he has to climb a large ladder to just get to the roof's edge to hit it with the hose. am i right mike? wish i had an answer for you as my home is very tall too and if i were to ever put pvs on the main roof i'd be in the same boat trying to get them clean. maybe you could talk to a major roofer or contractor and see if they have any good ideas. if you get some suggestions tell us about them even if you elect to not go along with it for it may work in other cases for other people.