Bird droppings on solar panels: the loss is bigger than the mess
Worse than the mess suggests. A dropping casts hard shade: one blocked cell can drag down its whole string and run hot. NREL puts typical soiling loss at about 5% of annual output, up to 25% in the dirtiest locations — and baked droppings sit at the bad end, because rain will not shift them.
Hard shade beats film for damage
Dust and pollen build a film. A film cuts light evenly — every cell loses a little, the panel keeps working, output drifts down. A bird dropping is a different problem. It is opaque. The cell underneath it isn't producing less; it's producing close to nothing. Panels are wired in series, so one starved cell throttles the cells around it. The dropping might cover a fifty-cent piece of glass. The loss does not stay that size.
Then there's heat. A shaded cell in a working string stops generating and starts dissipating — the string's current pushes through it and it warms up. Panel makers fit bypass diodes to limit this, and they help, but a diode protects the panel by cutting a chunk of it out of production. A dropping left through a Sydney summer means a hot spot cycling daily under glass. Cleaning fixes the shade. It cannot fix a cell that has already cooked. That is the argument for not leaving it.
Rain does not shift a baked dropping
Rain is decent at rinsing loose dust off tilted glass. It is useless against a dropping that dried through a warm afternoon. Droppings bake on. By the time a storm arrives, the deposit has bonded to the glass and the water flows around it. You can watch a panel come out of a downpour looking rinsed everywhere except the three white patches that matter most. Waiting for weather is not a maintenance plan. It is a delay with a power bill attached.
For scale: NREL, the US renewable energy laboratory, puts typical soiling loss at about 5 per cent of annual output, rising to 25 per cent in the dirtiest locations. Those figures cover ordinary grime — the even film rain does help with. Hard shading from droppings stacks on top of that, and it concentrates the loss instead of spreading it. An array under a flight path or a favourite perch isn't average. It carries the worst version of the problem until someone takes it off.
Getting it off without walking the array
The wrong way is common: climb up, stand on the panels, scrape at the deposit, hit it with a pressure washer. Every part of that is a mistake. Panel glass is built to take hail, not the point load of a boot. Dry scraping grinds grit across the anti-reflective coating. High pressure can drive water past the frame seals and stress the laminate. And a sloped roof is nowhere for a homeowner to be standing — least of all leaning over an edge with a scrubbing brush.
The right way is slower and gentler. Soften the deposit first, then lift it with a soft brush and pure water — no detergent residue left behind to grab the next layer of dust. Work from the ladder, the anchor points or a water-fed pole, never from the array itself. Rinse until the glass sheds water cleanly. Done properly, the panels come back to full light with the coating intact and nobody's weight ever on the glass. It is not complicated. It is just easy to do badly.
Put a number on it
What a fouled array costs you depends on your system size and your feed-in maths, and nobody honest will pretend to know your number without seeing the bill. What the clean costs is easier. Solar panel cleaning is priced per job — panel count, roof pitch, access, how much growth and grime has taken hold — because a flat rate would be wrong for half the houses in Sydney. Your roof is not an average, so your price shouldn't be either.
The instant quote handles it. Answer a few questions about the house and the array and it returns a firm, bookable price in about 60 seconds — a real number that holds unless the place turns out materially different from what you described. If the roof needs doing at the same time, bundling services on one visit saves 5 to 15 per cent. The birds will be back; that part is not negotiable. How long their mess sits on your glass is.