Solar panel cleaning restores output lost to soiling, using deionised water at low pressure so nothing abrasive or mineral-bearing touches the anti-reflective coating. It is a genuinely specialist job: the wrong water and the wrong pressure both cause permanent damage that costs more than the generation they recover.
What soiling actually costs
A photovoltaic panel converts the light that reaches the cell. Anything sitting on the glass reduces that, and the losses accumulate quietly — nobody notices a gradual decline in a number they rarely look at.
The heavier contributors here are spring pollen, agricultural dust, bird droppings and, on low-pitch arrays, general grime that rain does not carry off. Rain rinses light dust adequately; it does nothing for bonded droppings or a pollen film.
Bird droppings deserve separate mention because they are not merely a soiling problem. A fully shaded cell creates a hot spot, and repeated hot-spotting degrades the panel permanently.
Why deionised water and low pressure
Two rules govern this work, and both are about avoiding damage rather than achieving cleanliness.
Deionised water. Tap water — and especially the mineral-heavy well water common across this region — leaves deposits as it evaporates. Those deposits are exactly the soiling you were trying to remove, so the panel is dirty again as it dries. Deionised water has the minerals stripped and dries clear with no residue.
Low pressure and soft brushes. Panel glass carries an anti-reflective coating that is thin and easily abraded. High pressure, abrasive pads and household detergents all damage it, and the damage is permanent because the coating cannot be reapplied in the field. Most panel warranties specify cleaning method, and several are void if it has not been followed.
Ground mounts and solar farms
Ground-mounted arrays are the more sensible economic target. They are reachable without roof work, they soil faster because they sit closer to dust sources, and they are frequently larger installations where a percentage of output is a meaningful number.
Agricultural ground mounts in this region take a particular beating during planting and harvest, when field dust is heaviest.
For commercial arrays and solar farms, cleaning is a maintenance line item with a calculable return: the cost of the clean against the generation recovered across the interval until the next one. If you have production data, that calculation is straightforward and we are happy to work through it with you.
How often
Once or twice a year suits most residential arrays here, timed after spring pollen and, where relevant, after harvest dust.
Arrays near gravel roads, active fields or heavy tree cover want more frequent attention. So do low-pitch installations, which shed less on their own.
The honest guide is your own production data. If output is drifting below what the same month produced in previous years and nothing else has changed, soiling is the usual explanation.