Wind turbine blade cleaning: when it is soiling and when it is erosion
On a dirty blade two things coexist that look alike and have nothing in common: soiling, which is cleaned, and leading-edge erosion, which is repaired. Confusing them is expensive in both directions.
The blade is the part of a wind turbine where cleaning is most often confused with repair. Both look like "the blade is in bad shape", both start at the leading edge, and only one of them is solved with pressurised water. This article explains how to tell them apart.
What builds up on a blade
A blade cuts through the air at very high tip speeds, and everything in that air ends up on it: insects, pollen, dust, tree resin in some areas, salt near the coast and, in farmland, residues from crop treatments. Soiling concentrates on the leading edge and the first third of the suction side, because that is the zone that strikes first.
All of that is soiling: it sits on the blade, not in it, and comes off with water, detergent and controlled pressure. A clean blade recovers its original aerodynamic profile. That is what a blade clean does.
What is not soiling
Over the years, the continuous impact of rain, hail and particles wears down the leading-edge coating. First the paint pits, then the material underneath shows, and the edge stops being smooth. That is leading-edge erosion, and nothing washes it off: it has to be repaired, with tapes, coatings or fillers, and that is contact work that needs a technician on the blade.
From a distance, an eroded blade and a dirty blade look alike. Up close they do not: soiling is a layer on a smooth surface; erosion is a rough surface, sometimes with the laminate showing. A photographic inspection from a few metres tells them apart without doubt, which is why inspection and cleaning work well in the same visit.
Why telling them apart matters
- If a clean is ordered for an eroded blade, the client pays and the blade stays the same. An honest contractor should say so before starting.
- If a repair is ordered for a blade that was only dirty, a rope access set-up is rigged for something that could have been solved from the ground in a day.
- And if cleaning precedes repair, the repair is done on a clean surface, which is how it should be done.
On production
It is well known that a dirty blade has worse aerodynamics than a clean one, and that the effect depends on the machine, the type of soiling and the site. What we will not do is give you a percentage of recovered production, because we do not have our own measurement to back it. What we do measure from day one is downtime: one day per machine versus the 4-5 days of rope access. When we have our own production data, we will publish it with its method.
What to ask for
Photographs of the leading edge of every blade before cleaning, to know what is under the dirt; a clean with controlled pressure that does not damage the coating; and a report that says, blade by blade, whether what was found is soiling, erosion or both. That turns a cleaning into a maintenance decision.