Wind Blade Maintenance: Optional Or Mandatory?
By Gary Kanaby
Wind blade maintenance is often overlooked because blades are perceived as non-wear items that are made with weatherproof materials. The problem is that the other components of a wind turbine are more familiar because they are parts that are used in many other industries and the maintenance is well understood. We all know, for example, that we have to change the oil in a car’s transmission – the same principle applies to a gearbox in a wind turbine.
However, a blade is more complex and is made of composites. Most everyone understands on some level that the same fiberglass composite contained in a blade can also be found in boat building. However, the environments are not the same, and the stressors are different.
A wind blade has many forces on it, which eventually fatigue the materials until the composites lose the strength required to maintain the structure, at which time the blade will fail. The main force on the blade is gravity, which pulls the blade down in both directions as it rotates. This force has a big impact on blades, especially as their production becomes longer and larger.
Blades must contend with the force of the wind. If they are pitched properly, this will be under control. In most cases, if a blade is designed and built correctly, the composites will not be fatigued enough during their lifetime to fail. Therefore, why do we need maintenance?
The most prevalent wear on a blade is on the leading edge. The wear is caused by rain, snow, ice or particles in the air. Depending on the amount present, the erosion can begin to occur within a few years of installation and continue through the life of the blade. Each year, the erosion affects the leading edge and the airfoil of the blade. It has been found that over the life of a blade, the reduction of power production will be anywhere from 2% to 5%, depending on the site. This is significant. The reason it is not addressed in many cases is because the production loss is not detectable over the course of a year or two, but it is still happening.
The most prevalent wear on a blade is on the leading edge. The wear is caused by rain, snow, ice or particles in the air. Depending on the amount present, the erosion can begin to occur within a few years of installation and continue through the life of the blade. Each year, the erosion affects the leading edge and the airfoil of the blade. It has been found that over the life of a blade, the reduction of power production will be anywhere from 2% to 5%, depending on the site. This is significant. The reason it is not addressed in many cases is because the production loss is not detectable over the course of a year or two, but it is still happening.
The solution is to inspect the blades to detect such wear and not only repair the erosion, but also add leading edge protection (LEP). The payback is in the production increase over the next several years. LEP can last from five years to 10 years before recoating is required. By acting when the first signs are encountered, one will eliminate long repairs that might require the leading edge airfoil to be recreated, which can double the cost of the LEP.
Inspections also detect lightning strikes, which are another common problem. Knowing that lightning has struck a blade allows for the repairs to be scheduled and reveals that the lightning protection system may have been compromised. As blades age, other manufacturing defects start to appear. Scheduling services in advance can result in savings in downtime, as the repairs can be scheduled during the low-wind season, and grouping the repairs can save on mobilization costs for the services – that is, if the repairs can be delayed until then.
No matter the conditions at a site, owners and operators that regularly perform blade inspections, schedule repairs and apply LEP will come out far better than those that do not.
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Gary Kanaby is commercial manager for WindCom, a Houston-based services provider. He can be reached at (281) 227-5130 or gary.kanaby@v9d.d78.myftpupload.com.
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