Dust, pollen and hard water film settle on panel glass and block the light your array is there to collect. Panels are cleaned with deionized water and a soft brush, reached from ground level with the same water fed pole system used on high windows, so nobody walks on your roof and the rinse dries without leaving mineral spotting behind.
A solar panel is a piece of glass whose entire job is letting light through. Anything sitting on that glass is between the sun and the cell underneath it. In Central Texas that means pollen in spring, Saharan dust when it blows through, and the mineral film that sprinkler overspray leaves behind and that rain does not wash off.
Panels are cleaned with deionized water, a soft bristle brush and a soap chosen for what it does not do to the panel. Everything is reached from the ground where the pitch allows, so the array is cleaned without anyone standing on it.
Three things matter on a panel: the water, the brush and the soap. Get any of them wrong and you either leave spotting or you damage something.
Pure water is aggressive about picking up minerals, which is exactly what you want on a panel that has been sprayed by irrigation for two summers. It lifts the mineral film rather than smearing it, and because there is nothing dissolved in it there is nothing left behind when it dries. Hose water does the opposite. It dries and leaves its own spots.
Panel glass is tougher than window glass but the anti reflective coating on it is not. A soft bristle head agitates the film without dragging grit across the surface, and then the array gets rinsed for longer than most people would think necessary, because anything left in the frame channels runs back down the glass on the next rain.
This is the part almost nobody asks about. An array is not only glass. The frames, seals and junction housings are plastic, and ordinary detergents oxidize them over time, which is how panels end up chalky and brittle around the edges. The soap used here is chosen to protect that plastic rather than slowly degrade it.
Cleaning an array visibly lifts what it produces, and the dirtier it was the more obvious that is. I am not going to quote you a percentage, because the honest answer depends entirely on what was on your panels to begin with, how steep the pitch is and how long it has been. An array under oaks a hundred yards from a limestone road is a different problem from one on an open lot.
What is predictable is the direction. Anything opaque sitting on panel glass is light the cells never receive, and unlike a window, you are not looking at a solar panel every day to notice it getting worse. Most people find out from their production figures rather than from looking up.
Panels are not a walking surface. Standing on one can cause micro cracking in the cells that does not show from the ground and does not announce itself until output starts drifting down months later. Roof tiles and shingles do not enjoy the traffic either.
The same purified water fed pole system used on sixty foot glass reaches most roof mounted arrays from ground level, so the work happens without anyone up there. Where a pitch genuinely cannot be reached safely from the ground I will say so rather than improvise, and we will talk about whether it is worth doing at all.
Not the calendar. What is around the array, and what has blown through lately.
On an open lot with no irrigation reaching the roof and no heavy tree cover, an annual clean keeps an array honest. Late spring, once the oak pollen has finished, is usually the useful moment.
Sprinklers that reach the roofline, which leave mineral film rain cannot shift. Heavy tree cover, which means pollen and organic buildup. A construction site nearby. Or a Saharan dust event, which coats everything evenly and sticks properly if there was any humidity in the air while it landed.
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Once a year suits most arrays on open lots. Twice if sprinklers reach your roofline, if you have heavy tree cover, or if there is construction nearby. Late spring, after the oak pollen has finished, is usually the most useful single slot in the year.
Yes, and the dirtier the array was the more obvious it is. I will not quote you a percentage, because it depends entirely on what was on the panels, the pitch and how long it has been since the last clean. Anything opaque on panel glass is light the cells never receive, so the direction is never in doubt even when the size of it is.
No. Panels are not a walking surface and standing on one can cause micro cracking in the cells that will not show until production drifts down months later. The same water fed pole system used on high windows reaches most roof mounted arrays from ground level.
Because hose water carries dissolved minerals and leaves them behind as spotting when it dries, which is the thing you were trying to remove. Deionized water has nothing in it, so it lifts mineral film off the glass and then dries clear.
One chosen for what it does not do to the plastic. An array is not only glass, the frames, seals and junction housings are plastic, and ordinary detergents oxidize them over time until they go chalky and brittle at the edges. Panel safe soap protects those components rather than slowly degrading them.
Yes, and they are usually simpler since access is not the constraint. Ground and pole mounted arrays pick up splash from below as well as fallout from above, so the frame channels tend to need more attention than a roof array.
Not with a soft bristle head and pure water. Panel glass is tough but the coating on it is not, so anything abrasive, any pressure washing and any harsh chemical is the wrong tool. Grit gets floated off rather than dragged across the surface.
Yes. Larger arrays are priced by panel count and access rather than as a flat job, and they usually make sense on a schedule since the difference between a clean array and a neglected one compounds across a lot of panels.
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