Does Dirty Solar Really Cut Your Output? The Sunshine Coast Numbers

Why a little grime costs more than it looks like it should

The intuitive assumption is that if 5% of a panel's surface is covered in grime, you lose roughly 5% of that panel's output. On many systems that's roughly true for an evenly spread, thin layer of dust. But bird droppings, leaf debris and other concentrated spots behave differently: they create hard shading on specific cells, and depending on how the system's wired, a few heavily shaded cells can throttle the output of the whole string of panels connected to them — not just the cells directly underneath the mess. This is the main reason a seemingly minor amount of visible grime can translate into a output drop that doesn't match how "dirty" the panel looks from the ground.

What actually builds up on Sunshine Coast panels

What accumulates depends heavily on where the property sits. Coastal suburbs — Mooloolaba, Maroochydore, Caloundra, anywhere with a direct ocean breeze — get a fine salt film that builds steadily and, because normal rain doesn't fully rinse it off, keeps thickening over months. Further inland and in drier regional areas like Gympie, dust is the bigger contributor, especially after a dry spell. Everywhere on the Coast, bird droppings and pollen (particularly through spring) add to whatever the local climate is already depositing. Properties under trees get an added layer of leaf litter and sap, which is stickier and harder for rain to clear than dust alone.

Roughly what it costs in lost generation

As a general guide, based on typical patterns we see across the systems we clean:

• Light, even dust/salt film: around 5–10% output loss
• Heavier film after a long dry stretch with no rain: can push past 10–15%
• Localised bird droppings or debris on specific panels: can cost well over 20% on the affected string, due to the shading effect described above

For a standard 6.6kW residential system, even the lower end of that range adds up to a meaningful amount of generation over a year — and because solar savings compound daily, a dirty system keeps costing you every single day it stays that way, not just once.

Why plain tap water makes the problem worse over time

This is the part most people don't expect: washing panels with ordinary tap or bore water can actually make the long-term problem worse, not better. Tap water carries dissolved minerals that dry on the glass as a chalky residue — a process called calcification. Each wash with mineral-heavy water leaves a little more of this behind, and over repeated cleans it builds into a hazy, hard-to-remove film that permanently dulls the glass. It's why we use a purified, deionised water-fed pole system for every solar clean — the water has virtually no mineral content, so it dries completely spot-free and doesn't add to the problem it's meant to solve. See our solar panel cleaning page for how the system works.

When cleaning actually pays for itself

The honest answer is it depends on your system size, your electricity rate, and how dirty the panels actually are — which is exactly why we do a visual assessment before quoting rather than a flat per-panel price with no inspection. As a rule of thumb though: if it's been more than 12 months since your panels were cleaned, or you're in a coastal, dusty or heavily treed location, the cost of a clean is very likely to be recovered in extra generation well within a year, often inside a few months.