Know your blade: Understanding the risks of different blade technologies

Catastrophic wind turbine blade failures are typically seen as uncommon events.

Watch any local newscast of a reporter standing uncomfortably in a cornfield, a turbine with half its blade missing standing ominously in the background, you will often hear the question “How often does this type of thing happen?”

From a recently published study, blade failures were 40% of the value for insurance claims for the US onshore market. And from an anecdotal perspective across ONYX’s customer base, many are experiencing serial issues. In some cases, owner/operators have experienced multiple failures at individual wind farms within the last year.

As the installed base has grown and whether failures are serial issues, early life, or aging-related, understanding the risks and future costs of major repairs is ever more crucial for turbine owners. The downtime associated with a catastrophic blade failure can often be months, especially for out-of-production/hard-to-source blades, plus hundreds of thousands of dollars, to purchase the blade and for erection.

Get a Blade Health Maintenance Plan

So what are the differences between Blade A & Blade B shown in Figures 2-3?

The single shear web architecture, Blade A, has only one web bonded to both the SS and PS spar caps and is the simpler architecture.  For inspection there is only one main web bondline (where the spar cap abuts the shear web), however, there is no redundancy. If there are defects or damages in or near this bondline then the shear web can potentially detach. The resulting loss of structural integrity will lead to buckling of the shells and catastrophic failure.

The architecture with two main webs, Blade B, provides two bondlines to split the shear load that is transferred between the shear webs and the spar cap. Therefore, damages or defects found in a bondline with two main webs may be less likely to cause catastrophic failure. The other shear web provides another load path for that local region. This type of design is also more stable, providing a smaller trailing edge panel (the section between the shear web and trailing edge of the blade), which minimizes the potential of buckling of the panel under high loading or a defect in that region. The design is often heavier but brings benefits to reliability.  The inspection needs to consider both bondlines.

There are many other architectures for blades and they differ by manufacturer, age, load requirements, and the market they were designed for. The landscape is continually changing, as new technology is designed, so OEM’s can sell turbines with competitive CAPEX to and reduce the levelized cost of energy.

To help understand your fleet, we provide a brief description of architectures and pros and cons, as well as inspection tips below: