Is solar panel cleaning worth it on a Toowoomba roof?

The honest answer

It depends on what is actually on them

We are not going to quote you a percentage. Every array is different, the soiling is different, and any figure put on a website is somebody's best case. What we can tell you is what we see on Toowoomba roofs, and how to work out whether yours is worth doing.

Light, even dust does very little. Rain shifts most of it, and the loss is small enough that cleaning it is hard to justify on output alone. That is the case the sceptics are describing, and on a clean suburban roof in a wet year they are right.

Patchy, stubborn soiling is the opposite. Lichen at the frame edge, bird droppings, a band of baked-on agricultural dust along the lower edge, or sap and gum blossom under a tree — these do not rinse off, they concentrate in one part of the panel, and shading part of a panel affects far more than that panel's share of the array. That is the case worth cleaning, and it is common here.

Local conditions

What lands on panels in this region

Agricultural dust off the Downs. The westerlies carry fine soil off cropping country through the dry months, and it settles on everything facing the sky. Out at Wilsonton, Torrington, Westbrook and Oakey it is the single biggest factor. It is also the one that builds a film rather than a layer — dew wets it overnight, it dries on, and the next lot sticks to it.

Lichen and algae off the Range. Long dew and fog at 700 metres grow biological soiling on any surface that stays damp, and the aluminium frame edge of a panel is a perfect ledge for it. It starts at the frame and creeps inward, which is exactly the worst place for it because it shades the bottom of every cell in that row.

Pollen, gum blossom and sap. Spring in the Garden City puts a sticky layer on north-facing glass, and it is not something rain takes off. Anything under a gum gets sap and small bark as well.

Low-pitch roofs make all of it worse. The flatter the array, the less self-cleaning it is — water sits and evaporates rather than running off and carrying the dirt with it. Most newer estate homes have shallower roof pitches than older Toowoomba houses, which is why you often see it worst on the newest roofs.

How to decide

Four things that tell you it is worth doing

Your monitoring is down against the same month last year. This is the only figure that matters, and you already have it. Compare like with like — same month, similar weather — and if the array is quietly producing less than it did, soiling is the first thing to rule out because it is the cheapest to fix.

You can see green or dark edging on the frames from the ground. If it is visible from down there, it is well established up there.

Nothing has been done since installation. Plenty of Toowoomba arrays are now well past ten years old and have never been touched. Those are the ones where a clean makes a visible difference rather than a marginal one.

You are having other work done up there anyway. If the roof or the gutters are being done, adding the panels to the same visit costs far less than a separate trip — and the order matters, because a roof clean throws material onto the array.