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Wind Turbine Blade Inspections: Is it One-Size-Fits-All?



Historic Perspective

One aspect of the wind industry that is still maturing is blade inspections. Historically, the industry has not done a good job of maintaining blades. Preoccupation with gearbox failures and other mechanical and electrical issues, and a historical lack of blade experts within the power companies meant that blades were often an afterthought.


Decreasing the levelized cost of energy (LCOE) stands as the most important trend in the industry. One of the key elements in most OEMs’ LCOE strategy has been increasing annual energy production (AEP). The two most common improvement points are increasing the rotor size and the rated output of the generator. As the size of turbines and blades increased, the weight and cost of blades increased disproportionately to the energy capture. New solutions were applied to control the increase in the cost of blades, including the use of different materials, new structural designs, and changes in production processes. All these changes were made in the same timeframe across all of the industry and have resulted in an increase of blade damages.


The blade inspection solution typically employed in most annual maintenance schedules was annual binocular inspections from the ground. The main alternative – rope inspections – were costly and required significant WTG downtime. But the introduction of ground-based cameras and drones during the last couple of years has yielded a significant impact. Their use for blade inspections increased significantly the last couple of years as OEMs, asset owners and operators realized they needed to step up their blade inspection frequency and image quality to more proactively identify damages earlier. 


Most acknowledge that blades need to be adequately monitored in order to keep repair and replacement costs under control over the design life of the asset. Keep in mind that the largest driver of costs in a wind service contract over the lifetime of the asset are the main component failure rates. Of those components, the ones most easily inspected are the blades. This is not the case for gearboxes, generators, main bearings, and the likes.


A Better Path Forward

The inspection technology is now at a level where a fully autonomous drone can inspect all four sides of the three blades of a WTG with a 100m rotor within only 15 minutes. By applying this latest technology customers can reduce the WTG downtime needed for inspections. Numerous customers have realized this and have put their trust in SkySpecs during the last couple years, resulting in 25,000 WTG inspections since 2017.


This provides us with a unique set of data in the industry across numerous OEMs and blade types and manufacturers. We’ve acquired valuable insight into the damage history of various blade models. It includes damage propagation over time, which enables estimation of future damage development. With that, our team of blade experts has assessed the risk associated with various blade models, based upon which we recommend an inspection frequency for each model designed to manage the risk of a catastrophic failure or rapid propagation of damage.


Frequency of Blade Inspection: What to Consider

How often blades should be inspected, then, depends on the service business model of the owner, the budget and risk appetite. To illustrate, the cost of dealing with a single catastrophic failure at a wind farm will pay for years of annual inspections. Or the propagation of category 3 damage to category 5 will dramatically increase the cost of repair. Regarding the business model, there is a fairly big difference between a 2-year term during the warranty period and self-maintenance after this period versus a 25-year full-scope service agreement with an OEM – and of course, there is everything in between.


A long- term service agreement with the OEM provides two options:

1) When an owner extends the service contract, or signs a new one, incorporate drone inspections with an agreed-upon frequency. Although OEMs are under a lot of pressure to lower the LCOE in the O&M phase, most players now realize that regular drone inspections and data capture are a must in order to keep the blades and their own costs in check.

2) If the OEM is unwilling to include the inspections in the contract / amended annual inspection, the owner can do it on their own. If the service on one of the main components is falling short, fixing it and optimizing its lifespan is a worthwhile add-on to cover.


Service strategies can change over time. There are multiple options available in today’s market: OEM service, OEM Multibrand, Independent Service Providers or self-maintenance. Having a complete and transparent health track record of all of the blades in a portfolio will help owners make a better risk / return decision when picking the right service strategy going forward.


Contact Patrick Siep at patrick.siep@skyspecs.com