Apparently you should get a pro in. "...utensils may be needed that could cause issues with the panels if not used correctly. Unfortunately moss and Lichen cause large amounts of shading to panels and can have a detrimental effect on the performance." - Isobel
If you want to go up and clean panels but you’re concerned about roof safety, then fit an eyebolt on the opposite wall to your solar panels, near the bottom (in the mortar would be fine). Attach one end of a long rope to the eye bolt, then hurl rest of it over the rooftop to the other side and use a gadget like this rappelling rope.
Clean panels are a good thing. You're maximising their efficiency, when your own draw during the day is lessened and you can trickle in some export credit to help offset your non-solar consumption.
I too have noticed that some solar companies do recommend pro cleaning only, but then others don't. I think if people are careful and use some form of fall protection, then it's pretty straight forward and safe.
To me, solar panels are made to withstand harsh environments and need to be very tough, imagine the turmoil if there was a full on hailstorm and everyone's panels got wrecked.
The precaution of washing them early morning, early evening to avoid thermal shock, makes a lot of sense. As a bonus, there's less likelihood of smears being left on the glass.
I agree that cleaning agents need to be chosen with care, but a splash of dishwashing detergent in a bucket of water, won't do any damage & I can't see how it would. Rinsing it off after the clean is common sense, & using a squeegee to remove excess water will prevent smearing. To be doubly sure, wrap a slightly damp microfibre cloth around the broom head & sweep the panels to remove micro-droplets (if there were any). - Andy_Mann
I got some moss on my solar hot water system where the glass meets the frame. It will hose off easily or get burnt off with some decent sun. - Brad
Used to live in Canberra where lichen on tiled roofs was common - people would install a line of copper wire on top of roof and water running down roof would carry minute amounts of the copper down the roof and slowly kill and remove the lichen. - PappaGabba