The way not to scratch solar panels when cleaning is to control the one thing that touches the glass: rinse loose grit off first with clean low-mineral water, use a soft-bristle brush and a smooth rubber squeegee on a telescopic pole, and keep pressure washers, scouring pads, dirty cloths and abrasive cleaners away from the panel. Scratches and micro-scratches reduce light transmission permanently, and the damage usually starts at the point where the wrong tool meets a thin layer of dust.
I learned this the slow way. A few years ago, before I thought about the contact point, I used a bucket of tap water and an old sponge that had been lying near the garden. The panels looked clean afterwards, but at a low sun angle later that afternoon I could see fine swirl marks. They were not dramatic, but they were there, and they do not heal. That is the point of this article: not a full cleaning tutorial, but how to stop the scratch before it happens.
Why the point of contact matters
Solar panel glass is not a car windscreen. Most modules have an anti-reflective coating on the front glass to improve light transmission. That coating is thin and softer than the glass underneath. When you rub a dirty cloth, a scouring pad, or even a clean-looking brush that has picked up grit, the grit acts like sandpaper. You may not see the damage immediately, but every pass scatters a little more light away from the cells.
I live in a part of South Africa where winter dust is a reality. It comes off gravel roads, dry veld, construction sites and roof tiles. Left on the panel, it is harmless until something moves it. The safest cleaning sequence is to get that dust off with water before anything solid touches the glass.
The rinse that does the real work
The most important step is not scrubbing. It is rinsing. I start with clean, low-mineral water. In many South African towns, municipal water has a high calcium or magnesium content, and borehole water can be even worse. If you rinse a panel and let it dry in the sun, the water evaporates and leaves behind calcium or salt residue. That residue is not just a cosmetic mark; it attracts more dust and gives the next cleaning more grit to work with.
Rainwater collected in a clean tank is my first choice. If I do not have rainwater, I use reverse osmosis or softened water if it is available. If I only have tap water, I still rinse, but I make sure to squeegee the panel dry before the water can evaporate. The key is not to let mineral-rich water dry on the glass.
The tools I will and won't let near the glass
Once the loose grit is rinsed away, I use a soft-bristle brush on a telescopic pole. The bristles need to be soft enough to bend when they touch your palm, and they need to be dedicated to the panels. If the brush falls on the ground, I rinse the bristles before it goes back up. A brush full of sand is worse than no brush at all.
After the brush, I use a smooth rubber squeegee on the same telescopic pole. The squeegee blade should be clean rubber with no nicks or hard edges. This is the only other thing that touches the glass. Not a sponge, not a chamois, not a microfibre cloth that has been through a dusty laundry basket. Those materials hold particles and rub them into the surface.
I do not use pressure washers. I do not care how far away the nozzle is or what setting the machine has; at the glass, the answer is no. Pressure washers can force water past the module seals, damage junction boxes, and strip anti-reflective coatings. The damage may not be visible on the day, but it shows up later as moisture ingress or a dull patch where the coating is gone. A pressure washer turns a cleaning job into a slow panel failure.
I also reject abrasive cleaners and scouring pads outright. Anything labelled as a 'panel restorer' or a 'glass scrub' that feels gritty is not coming near my roof. If water and a soft brush cannot shift a mark, I let the mark sit and reassess rather than reach for something harsher.
When hot panels become streaky panels
I do not clean panels in the middle of a Highveld afternoon if I can avoid it. The glass gets hot, and any water or cleaning solution I apply evaporates before I can rinse it off. That leaves streaks and mineral deposits, even with low-mineral water. It also means I end up making more passes with the squeegee, which is more opportunity for trapped grit to scratch the surface.
Early morning or late afternoon is better. The panels are cooler, the water stays liquid long enough to carry the grit off, and I can see the surface without the glare. If the panels are already hot and there is bird droppings or heavy dust, I either wait or I use a light mist from a hose first to cool just the glass, then clean. But I do not use a pressure nozzle for that, only a gentle open hose.
What to check before you even wet the glass
Before any cleaning, I do a visual check from the ground. I look for bird droppings, cracked glass, loose modules, or debris like leaves and twigs sitting against the panel edges. Bird droppings are common from hadedas and pigeons in many South African neighbourhoods. If I see a cracked panel, I stop. Cleaning a cracked panel can push water into the crack and make the damage worse, and it is not a cleaning job anymore, it is a replacement discussion.
Dried bird droppings need patience. I soak the spot with water and let it soften before I use the soft brush. Scrubbing harder with a brush or cloth turns the grit in the droppings into an abrasive paste. In coastal areas, salt film can also build up. The same principle applies: rinse first, soften, then use soft contact.
When the panel is not reachable from the ground
I clean from the ground or a stable flat surface with a telescopic pole. If a panel cannot be reached safely that way, I call a qualified service provider with the right equipment. I do not put an unsecured ladder against the gutter and stretch. The risk is not worth the cleaning. And I stay away from the wiring, connectors and inverter side entirely. This is a glass cleaning routine, not an electrical inspection.
The real lesson is that solar panels rarely need aggressive cleaning. In most South African homes, a good rinse, a soft brush and a smooth squeegee every few months is enough. The scratches people get are usually not from cleaning too little; they are from cleaning with the wrong tool once. If you control the point of contact, you protect the glass and the output that comes through it.
