Once every 4 months or so I venture onto my Roof to clean my photovoltaic panels. All I use is a bucket of water and an extended glass cleaner tool.
Step 1: Begin Cleaning.
Just like I would a large glass window or my car's windshield, the cleaning is easy. There are always some hard grime spots that have to be picked by hand.
Step 2: Cleaned!
Now one of my Panels is clean. I have 8 total and it took me 25 minutes to calmly clean all of them.