INTRODUCTION AND OVERVIEW ON ROTOR-BASED METHODS

In times of zero subsidy bids and lowest cost of energy competition in the wind industry the margins of wind farm business cases are becoming rather tight. It is not enough anymore to simply keep the availability of the wind turbines on a reliable and high level to meet the business case expectations. Well, this paves the way for wind turbine optimisation measures in order to regain the last 5-10% losses that a wind turbine might suffer as well as to tap additional performance potentials hidden in the turbine design. In addition, there is usually an indirect added value, as such improvement measures are usually not only increasing the annual energy production (“AEP”), but also reduce loads and stress considerably in the wind turbine components. Such indirect profitability lowers the cost and increases the value of wind farm assets by less wear & tear, therefore lesser maintenance & repair efforts and higher availability. On top longer component lifetime yield potentially additional years of operation, which all adds up to a better business case for your wind assets.

If dealing with wind turbine performance improvements, there are a couple of questions, that owners & operators usually would like to get answered before they are entering into such an investment:

• What are now the root causes for underperformance in wind turbines?
• Where can we find additional percentage points beyond the warranted power curve?
• Which methods and tools are available on the market?
• What is the improvement potential for my wind farm / turbine types?
• How can the performance improvement reliably be validated?
• What risks have to be considered in applying these measures?
• What is the return of investment, the business case for the application of such methods / tools?

To answer these questions, you need to be an expert in the field and even those struggles to keep an overview on the various tools and methods offered in the wind industry.

Overview rotor-based performance improvement methods:

The following table shall give an overview on methods to improve the performance of wind turbines mainly in terms of the annual energy production (AEP), but also in terms of more availability (AV) in case of curtailment, noise reduction (N) and extension of component lifetime (LT). But it might also be the case, that the tool described simply serves to increase the safety of the wind turbine or to comply mandatory safety requirements (S).

Rotor based improvements are understood as being applied in the rotor plane mainly. Most of them have their physical background logically in the domain of aero-dynamical improvements.

Adding up all the methods one easily collects 10-15% improvement potential accompanied by considerable investment cost. Hence, the question about the business case for the application of such methods needs to be answered and we also need to have a look into how such improvements can be optimally validated and what uncertainties need to be considered. We will have a look into the tools, methods available today on the market for performing power curve / performance comparisons in upcoming posts over the next couple of weeks. It is one of the biggest challenges for the industry to validate any performance improvements as real AEP gains conclusively, since the major uncertainty in the performance calculation is coming from the wind measurements itself. Comparing just on the power level is certainly possible as well but requires at least two wind turbines with almost the same wind conditions and at least one year of measurements. Otherwise the uncertainties of such methods would easily exceed the actual improvements resulting in an inconclusive validation. As volatile, changing and dependent from so many factors as the wind is, it is therefore quite difficult to come up with methods that are able to validate smaller improvement steps in the range of 1%.

Conclusion:

The retrofit market for the wind industry offers a lot of tools and methods to improve different weaknesses of the original wind turbine design or to tap additional performance potentials. However, it is tremendously important to understand, where the underperformance of the wind turbines is coming from or where such additional potentials can be tapped to apply the right tools and methods. Therefore, a detailed analysis of each specific wind farm with its usually unique environmental conditions based on the existing information is highly recommended. Based on this, the right approach to validate the benefits of the applied methods is equally important to justify the investments.

References

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