How to tell if your solar panels need cleaning

The clearest sign your solar panels need cleaning is a drop in output on sunny days compared to the same time last year, with no change in weather or shading. The second sign is the obvious one: you can see a film, pollen, or bird droppings when you look up from the ground.

Most Brisbane homeowners never check either. Panels sit on the roof out of sight, quietly losing a few percent a month, and the first hint of a problem is a power bill that crept up. Here is how to actually tell, without getting on the roof.

Sign 1: your monitoring app shows lower output on equivalent days

Almost every system installed in the last decade has a monitoring app, whether that is Fronius Solar.web, Enphase Enlighten, SolarEdge, or your inverter brand's own portal. This is the single most useful tool you have.

Open it and compare a clear, sunny day this month against a clear, sunny day from the same month last year. Pick days with similar conditions, because a cloudy day will obviously read lower for reasons that have nothing to do with grime.

A small drop is normal. Panels degrade slightly every year as a matter of physics, usually well under 1% annually. But an unexplained fall of 5% or more on equivalent sunny days, with no new shading and no fault codes, is a strong hint that soiling is the cause. If you have never cleaned the panels and the system is a few years old, that is exactly the pattern you would expect from accumulated dust, pollen, and bird fouling.

Set a calendar reminder to check the app once a month. It takes two minutes and it is the best maintenance habit you can build.

Sign 2: the generation curve looks jagged instead of smooth

On a cloudless day, a healthy system draws a smooth bell curve in the app: output climbs through the morning, peaks around the middle of the day, and tapers off into the evening.

If you see a smooth curve that simply sits lower than it used to, that points to even, all-over soiling like dust or pollen. If you see sharp dips or a jagged, spiky shape on a clear day, that often means localised shading, and a line of bird droppings across a few cells is a common culprit. Localised soiling is the worst kind, because shading even one cell can drag down the output of a whole string of panels.

Either pattern is worth investigating. A clean curve that has dropped is usually a cleaning job. A jagged curve might be cleaning, or it might be a hardware fault, which is the sort of thing a professional notices during a visit.

Sign 3: what you can see from the ground

You do not need to climb up to inspect your panels, and you should not. Stand back in the yard on a bright day, ideally with the sun behind you, and look at the glass.

Things to look for:

• A dull or hazy surface instead of clean reflective glass. A thin film of dust and pollen reads as a loss of shine.
• Dark spots or streaks, which are usually bird droppings. These tend to concentrate along the bottom edge of the array where birds perch and nest.
• Green tinges or lichen around the frame edges, more common on shaded, south-facing roofs in suburbs like Bardon and The Gap.
• Leaf litter or seed pods caught in the gaps, especially under mature trees.

A pair of binoculars makes this easier and keeps both your feet on the ground.

Sign 4: it has simply been too long

Sometimes the honest answer is just time. If you cannot remember the last clean, or the panels have never been cleaned since installation, they need attention regardless of what the app says.

Brisbane's climate works against you here. The dry season lays down dust, the jacaranda and other spring trees drop pollen across the Inner West, and our short, heavy storms tend to leave a muddy film rather than rinsing panels properly. For a sense of the right rhythm once you are back to a clean baseline, see our guide on how often you should clean solar panels in Brisbane. The short version is twice a year for most homes here.

How much output are dirty panels actually costing?

This is the question that makes the difference between "I should get to that" and "I am booking it." Australian research puts the loss from soiled panels somewhere between 5% and 25% of rated output, depending on how bad the build-up is and how the panels sit on the roof.

The angle of your roof matters more than people expect. Panels on a decent pitch shed a fair bit of loose dust when it rains. Panels mounted nearly flat hold water, dry to a film, and benefit far more from a manual clean. We have put the dollar figures together in how much production loss dirty panels are costing you if you want to run the numbers for your own system.

When to clean yourself and when to call someone

If you have a single-storey home with safe roof access and you are comfortable up there, a soft brush and clean water twice a year is a reasonable DIY job. Never use a pressure washer, and avoid tap water where you can, because the minerals dry to a haze.

For a two-storey Queenslander, a steep pitch, or any situation where you are not confident, get a professional in. Falls from residential roofs cause serious injuries in Queensland every year, and the value of a slightly cleaner panel is not worth that risk. A good operator also doubles as a quick condition check, spotting loose brackets or early faults while they are up there.

If the signs are pointing one way and you would rather hand it off, we can connect you with a local team that handles solar panel cleaning in Auchenflower and the surrounding Inner West suburbs. No pressure to book.

The two-minute version

Check your monitoring app against the same month last year. If sunny-day output has dropped 5% or more with no new shading, suspect grime. Look at the glass from the ground for film, droppings, or lichen. And if you simply cannot remember the last clean, it is time. Get the panels back to a clean baseline first, then settle into a twice-a-year habit.