First Airborne News

The implications of not being ‘pitch perfect’

When we looked at developing a solution to solve issues with WTG blade pitch misalignment (BPM) we needed to ask ourselves two questions:

  1. How common is this problem?
  2. What are the economic impacts for our customers with regards to the remaining useful life (RUL) and annual energy production (AEP)?

The collective experience of our team made it moderately easy to answer the first question. 

‘Moderately’ is the operative word here because despite the fact the physics of the issue are known and undeniable. The rate at which the global wind industry has grown, means that being able to identify individual blade pitch misalignment issues amongst fleets of 100’s if not 1000’s of turbines, has become a complex and costly task to execute at scale. 

Ironically, the size of these aforementioned projects goes a long way in helping to answer the second question with regards to longevity.

Economic Impact: RUL

In 2021, the European Academy of Wind Energy (EAWE) published a research article addressing this topic directly. They looked at the impact of individual blade pitch angle misalignment with respect to the turbine's useful life.

The data set of more than 1100 turbines was filtered down to 195 turbines representing a fleet of turbine types that needed to be assessed for a lifetime extension today or within the next few years, most of which were located in northern Europe. The set contained 22 combinations of turbine and blade types in the power range between 0.9 and 2.5 MW 

A significant percentage of the 195 WTGs analyzed during the study had misalignment, with over 40% having a misalignment of more than 0.6 degrees.

Seven imbalance scenarios were defined based on the misalignment data and were used to model the effect on the life of the turbines. 

The results found that the rotating components, such as the mainframe and power base, were most affected by the misalignment.

Economic Impact: AEP

So the business case was clear with regards to longevity issues, but what about the impacts with respect to annual energy production (AEP)?

It’s no secret that today there are bold and somewhat questionable claims being made frequently by technology suppliers claiming they impact AEP increases. Slogans like “Use our product/service and see X% AEP Increases” are being touted on websites and sales material, at every corner.

The skepticism comes mainly from the specificity of the numerical claim. And there's a reason behind this position.

Firstly, the approach we prefer to take is to look at third-party, credible data from an unbiased source and reverse engineer the findings.

Once again, the EAWE article provides valuable context to the AEP discussion.

By looking at the findings of the same group of scenarios as the above, one would expect to see those with largest misalignment deviations correlating to the largest AEP losses. 

In fact, the findings were not that black and white.

As illustrated above, all cases lead to a decrease in energy production. With the largest loss amount to 1.2% which occurs in scenario 2.1.

But interestingly, we can see that the biggest loss is not necessarily caused by the biggest deviation, which means that the direction of the pitch deviation plays a significant factor. 

Scenario 1.1 with the deviation of 1° has a larger impact compared to scenarios 2.3 and 2.4 with a deviation of 2°. 

The noticeable difference observed here is that with scenario 1.1, there are 2 blades deviating towards negative, while in the other two cases the signs are either opposite or towards positive.

The final takeaway was when we look at scenarios 2.2 and 2.5 we can see that the annual energy loss is pretty much the same and amounts to about 0.6%.

But when we are looking at their breakdown over the different wind speeds:

The differences are clearly highlighted for each scenario in every wind speed segment. 

What this indicates is that if we had performed a test in these two scenarios under specific wind speed conditions, in the range between the cut in of 6mps, the results of case 2.5 would even be an increase in energy. 

What this study demonstrates is that both factors, pitch deviation angle and wind distribution, play a very important role in energy production on their own as well as combined. 

Not only are there many other misalignment scenarios besides these specific seven, the varying wind regime of different sites makes it extremely difficult to assign a numeric value to AEP increases or decreases.

So where does that leave our conclusions and why did we create our solution, 1st Pitch.

What we know for certain is that aerodynamic imbalance reduced the RUL in most imbalance scenarios compared to the design situation. These imbalance scenarios had less impact on rotating components compared to non-rotating. Pitch angle towards stall position compared to feather suffered a more severe impact on RUL.

On the AEP side we see increases or decreases depending on the wind speed and misalignment direction, but the total energy production across all wind speeds was always negative. 

Perhaps the most concrete finding is that the scenario leading to the highest loss in RUL also leads to the highest loss in AEP. 
For our customers, this means that if they are able to ascertain which WTG’s in their fleet seem to be impacted by one of these factors, it’s a strong indication that the other may also exist.

Naturally, being able to detect blade pitch misalignment issues at a higher frequency and across large scale wind farms is critical and it’s the reason why 1st Pitch, part of the Resident Airborne Services stack, is available to our customers today.