Solar panel cleaning in Mallorca

What dirt actually does to your system

A PV module turns the radiation passing through its glass into electricity. Anything sitting on top intercepts that radiation before it reaches the cell. But not all soiling does the same damage, nor in the same way.

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  CalimaSaharan dust intrusions leave an extremely fine, even film. You can barely see it from the ground — which is exactly why it goes unnoticed. It covers 100 % of the collecting surface.
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  Sea saltNear the coast, marine aerosol deposits salt on the glass. As it dries it crystallises into a bonded layer that rain no longer washes off.
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  Dust and soilUnsurfaced tracks, building work and a rainless summer: the soiling piles up in exactly the months of highest radiation, when the system should be producing most.
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  Bird droppings and leavesThey cover very little area, but they are opaque. This is the case that does the most damage — and the reason is electrical. See below.

Two different ways of losing output

1. Transmittance loss. A thin, even layer — calima, dust, salt — lets less radiation through to the module as a whole. The loss is proportional to the soiling: light film, small loss. The catch is that it is constant, every sunny day, and it accumulates through the dry months without ever announcing itself.

2. Concentrated partial shading. This is where the damage stops being proportional. The cells in a module are wired in series, so the same current has to flow through every one of them. If a bird dropping or a leaf covers one cell, it can no longer supply that current and instead limits the current of its whole string; the current the other cells keep generating forces it into reverse bias, at which point the cell stops producing and starts dissipating energy as heat. That is a hot spot, and sustained over time it can brown the glass and degrade the encapsulant.

To prevent that, modules carry bypass diodes that short out the affected string. They do their job — they protect the panel — but bypassing a string means you stop producing with all of it. Which is why a mark the size of a coin can cost you far more than the area it covers.

Worth saying plainly: those figures come from general studies, not from a measurement of your roof. Every installation loses what it loses depending on orientation, tilt and surroundings. We are not going to quote you an invented percentage — we assess it on site, with your system in front of us.

How to clean a panel without ruining it

Module glass is not ordinary glass: it carries an anti-reflective coating on the outer face. Scratching it or attacking it with the wrong product is permanent damage, and cleaning harder won't undo it. That is why manufacturers publish fairly strict cleaning instructions. They are the ones we follow.

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  Low-hardness waterManufacturers ask for total hardness below 75 mg/L, or deionised water. Mains water in the Balearics is well above that — among the hardest in Spain. As it evaporates it bakes limescale onto the glass, and that scale won't come off with more water.
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  No abrasives, no aggressive chemicalsA soft brush and, if needed, a neutral detergent. Never a scouring pad, hydrochloric acid, ammonia or caustic soda: they take the anti-reflective coating with them.
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  Only on a cool moduleEarly morning or late afternoon. Throwing cold water at glass sitting at 60 °C is thermal shock for nothing; the manufacturer caps the difference at 20 °C. It also means we don't interrupt production during the good hours.
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  Nobody stands on the modulesThe glass takes the weight, but the silicon wafer underneath is around 170 microns thick and does not. Standing on it creates microcracks — invisible to the eye — that break the current paths, reduce output and can end in hot spots. For many manufacturers it also voids the warranty. We work with a pole, from outside the panel array.

The specific limits — total hardness < 75 mg/L, a maximum 20 °C temperature difference, maximum 35 bar at the nozzle, and the ban on abrasives, hydrochloric acid, ammonia and caustic soda — are taken from First Solar's module cleaning guidelines (PD-5-804 rev. 3.4). Every manufacturer has its own, and it's worth checking the ones for your specific module.