A mate of mine just paid $350 to have his solar panels cleaned. “They were filthy,” he told me. “The guy said I was probably losing 30% of my output.” I smiled politely, went home, and did some maths. Because that 30% figure? It’s rubbish.

Let me walk you through what the research actually says, and when cleaning does — and doesn’t — make financial sense.

What the science says

Multiple studies have looked at the impact of soiling on solar panel output. The general finding for Australian conditions is that dust and grime reduce output by 2-5% on average. In particularly dusty areas (think western NSW, parts of Queensland), it can reach 8-10%. After significant events like dust storms or bushfire smoke, losses can spike temporarily.

But 30%? That would require your panels to be genuinely caked in something. Bird droppings on individual cells can cause localised hot spots, and heavy pollen or tree sap buildup can be worse than dust. But for typical suburban panels getting rained on periodically, we’re talking single-digit percentage losses.

Running the numbers

Let’s use my mate’s system as an example. He’s got a 6.6kW system in suburban Brisbane, generating roughly 25 kWh per day on average.

At a self-consumption rate of about 40% and electricity price of 30 cents/kWh, his solar saves him about $3.00/day in avoided grid purchases. The other 60% is exported at 6 cents/kWh, earning about $0.90/day. Total daily value: roughly $3.90, or about $1,425 per year.

If his panels were genuinely producing 5% less due to soiling, that’s a loss of about $71 per year. To recover the $350 cleaning cost, his panels would need to be losing about 25% of their output. Which they weren’t.

Even in a generous scenario where cleaning restores 8% of lost output, that’s $114 per year. The cleaning cost still doesn’t pay for itself unless the panels were in seriously bad shape.

When cleaning IS worth it

There are situations where paying for panel cleaning makes sense:

Bird problem areas. If you’ve got a massive fig tree nearby and birds are using your panels as a toilet, the droppings can cause real damage (hot spots) beyond just output loss. Regular cleaning in this case is protective maintenance.

After major events. Bushfire ash, major dust storms, or construction dust from nearby building work can coat panels heavily enough to justify cleaning.

Flat or low-pitch roofs. Panels on steep roofs get natural rain washing. Panels on flat or near-flat roofs (common on commercial buildings) collect grime that rain doesn’t clear. These benefit more from cleaning.

Agricultural areas. If you’re near farms with pesticide spray, harvesting dust, or animal operations, soiling rates are genuinely higher.

The free alternative

Rain. Seriously. In most of coastal Australia, regular rainfall does a perfectly adequate job of keeping panels clean enough. Brisbane gets about 120 rain days per year. Melbourne gets about 150. Sydney around 130. That’s a lot of free cleaning.

If you want to do something yourself, a garden hose from the ground is fine for most single-story installations. Don’t use high pressure. Don’t use detergent (it can leave residue that actually attracts more dirt). Just plain water, early morning or late afternoon when panels are cool.

Never get on your roof to clean panels unless you’re qualified for working at heights. Falls from roofs kill people every year. No amount of solar output is worth that.

My approach

I clean my panels exactly once a year, in spring, with a hose from the ground. I can reach most of them from a safe position. I also keep an eye on my monitoring data — if I see a sudden drop in output that doesn’t correlate with weather, I’ll investigate.

In three years, I’ve cleaned them three times. My system’s output has degraded by about 1.5% total, which is bang on the expected annual panel degradation rate. The soiling impact is lost in the noise.

The bottom line

For most Australian homeowners in suburban areas with adequate rainfall, professional panel cleaning is an unnecessary expense. The marketing claims of 20-30% output loss are wildly exaggerated for typical conditions.

Save your $350. If you really want to optimise your system’s output, spend that money on monitoring software and learn your consumption patterns. That’ll save you far more than a clean set of panels ever will.