Does cleaning your solar panels actually make a difference to output?

Panels that have never been cleaned commonly sit 15 to 25% below rated output. That is the figure worth caring about.

Panels cleaned within the last twelve months typically recover 3 to 8%. Still worth doing, but it will not transform your bill.

The variable is what is on them. Uniform dust costs you a few percent. Bird mess and lichen create hard shading, and because panels are wired in series, one heavily shaded cell drags down the whole string.

Melbourne tap water carries dissolved minerals. When it dries on glass it leaves deposits, and those deposits reduce light transmission. You can end up marginally worse than before.

Deionised water has the minerals stripped out, so it dries completely clean with no spotting. That is why it is the industry standard rather than an upsell.

The other risk is the roof itself. More people are injured falling off roofs cleaning panels than any efficiency gain justifies.

Check your inverter app. Compare this month against the same month last year. A steady year-on-year decline that is not explained by weather usually means soiling.

Look for droppings and lichen rather than dust. Hard shading costs far more than an even film.

North-facing panels at a shallow pitch collect the most, because rain runs off too slowly to self-clean.