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Cleaning Solar Panels: Harmattan, Soot and Rain
Panels have no moving parts, so people assume there is nothing to maintain. Mostly true. There is exactly one job, and skipping it costs more than any other thing you can neglect.
A panel makes power from light reaching the cells. Anything in the way reduces it, in direct proportion. Not dramatically, not with an alarm, just a little less every week until the numbers stop making sense.
Three things land on your panels here
Harmattan dust arrives between roughly December and February, and it is fine enough to settle as an even film across the whole surface. Even coverage is the dangerous kind, because there is no obvious dirty patch to notice.
Soot is the Port Harcourt problem, and it behaves worse than dust. It is oily, so it sticks, and rain does not wash it off. It smears. Anybody here who has wiped a windowsill knows exactly what it does to a panel lying flat in the open.
Everything else. Bird droppings, leaves, and whatever the neighbour’s generator exhausts. These are worse than they look, because a single opaque spot can shut down a whole string of cells rather than just its own patch.
What it actually costs you
A light film of dust takes a few per cent. Nobody notices that, and nobody should worry about it.
This has a name and a body of research behind it. Soiling loss is measured seriously in the solar industry, and the figures from dusty regions are worse than most owners would guess.
A season of harmattan with no cleaning is a different matter, and a soot film on top of it worse again. Twenty per cent is not unusual, and we have seen worse on panels near a busy road that had not been touched in a year.
Twenty per cent of your generation is twenty per cent of the reason you bought the system. It shows up as the battery not quite filling, then not reaching morning, which people blame on the battery. It is the same misdiagnosis as the rainy season, arriving from a different direction.
When to clean, on a Nigerian calendar
| When | Why | How urgent |
|---|---|---|
| End of harmattan, around February | The heaviest dust load of the year has just finished settling | The most important clean you do |
| Before the rains, around April | Going into the low sun season with the panels as clean as possible | Worth doing |
| Mid rainy season, if you are in a soot area | Rain smears soot rather than removing it | Port Harcourt and Lagos, yes |
| After anything obvious | Bird droppings, a leaf fall, nearby building work | As soon as you see it |
If you have monitoring, you do not need the calendar. Watch your daily generation across a few clear days, and when it drifts down without the weather explaining it, that is your reminder.
How to do it without damaging anything
Early morning or evening, never the middle of a hot afternoon. Cold water on hot glass is how panels crack, and that is not a warranty claim you will win.
Plain water and a soft brush or cloth. Rinse the loose dust off first so you are not dragging grit across the glass, then wipe gently. For soot you may need a drop of mild detergent, and a second rinse to clear it.
Never a pressure washer. Never an abrasive pad, never a scraper, and nothing solvent based. The anti-reflective coating on the glass is what makes the panel efficient, and once you have scratched it through, no amount of cleaning brings the output back.
The part where you should not go up there
Most panel damage we see was done by somebody cleaning them, and most roof injuries happen to people doing a two minute job they had done safely a dozen times before.
If your roof is steep, high, or the panels are hard to reach, this is not the money to save. Get somebody with the right ladder and a harness. A cleaning visit costs a fraction of a cracked panel and considerably less than a fall.
Put it in your calendar, twice
February and April. Add a third around July if you are somewhere sooty.
That is the entire maintenance schedule for the generating half of your system. Everything else looks after itself, which is worth remembering the next time somebody tries to sell you a service contract for panels with no moving parts.
If your output has dropped and cleaning has not brought it back, something else is going on. Testing the panels is the next step, and we can talk you through it.