Published · Last updated · By the Big Deal Exterior Cleaning team, Sydney
How much output soiling actually costs
A solar panel converts the light that reaches the cell. Anything sitting on the glass — dust, pollen, salt film, bird droppings, lichen creeping in from the frame edge — is light that never arrives. Across typical Sydney conditions that soiling loss runs 15 to 25 percent, and considerably more where bird activity is heavy.
The financial framing is straightforward. On a 6.6kW system generating roughly 9,000 kWh a year, a 20 percent soiling loss is about 1,800 kWh — comfortably more than the cost of an annual clean at current Sydney electricity and feed-in rates.
| Contaminant | Typical impact | Removed by rain? |
|---|---|---|
| General dust and pollen | 5–10% loss | Partially |
| Coastal salt film | 8–15% loss | No |
| Bird droppings | Can disable a whole string | No |
| Lichen at frame edges | Progressive shading | No |
| Construction or bushfire ash | 10–20% loss | Partially |
| Tree sap and leaf residue | Localised hot spots | No |
Why rain does not do the job
Rain rinses loose dust but leaves a mineral film behind as it evaporates, which is why panels often look worse a day after rain than before it. Rain also cannot shift anything bonded to the glass — salt, bird droppings, sap or lichen — and in Sydney it arrives in short bursts followed by dry spells, which is the worst pattern for panel cleanliness.
Bird droppings are the case that matters most
A single bird dropping covering one cell can shut down an entire string of cells through the panel's bypass diode. That means a few square centimetres of mess can cost a disproportionate share of that panel's output — and in a series-wired array, the effect propagates further.
Sydney arrays are particularly exposed because the gap between panel and roof is an attractive nesting space for pigeons and mynas. If you can hear activity under the array, cleaning alone is not the answer and bird proofing should be quoted alongside it.
How panels should be cleaned
Solar panels are cleaned with deionised water and soft brushes only. No detergents, no abrasive pads and no pressure washing — all three risk scratching the anti-reflective coating, and all three give an installer grounds to question a warranty claim.
- Deionised water so nothing dries into a mineral film
- Soft brush heads that will not scratch the anti-reflective coating
- No detergents, solvents or abrasives on the panel surface
- Early morning or late afternoon, so panels are cool and not thermally shocked
- Frame edges and gutter lines cleared of lichen and debris
- Visual inspection for cracking, delamination and hot spots, reported with photos
Want this done properly?
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