Wind Energy

28
Turbulence Correction for Power Curves
K. Kaiser, W. Langreder, H. Hohlen and J. Højstrup
Summary. Measured power curves depend on more site-specific parameters than
covered by international standards. We present a method to quantify the combined
influence of three effects of the turbulence intensity. The method has been tested for
different types of turbines with good results. Hence the uncertainty related to site
specific turbulence on the power curve can be reduced.
28.1 Introduction
Precise power curve measurements and verifications are important for investors,
bankers and insurers. Most contracts specify a procedure according to
the IEC regulation [1], to verify the power curve of the purchased WT either
on site or under standard conditions. However the IEC regulation does not
cover all effects on the measurement relating to site specific wind climates
e.g. turbulence. It is known that both anemometers and WTs respond to
turbulence in very specific ways. Hence measurements of the power curve will
be affected by turbulence, which is related to the topography of the site [2].
The impact of turbulence on the anemometer has been described e.g. in [3].
The qualitative response of WTs to turbulence is known. Due to the complexity
of a WT system a quantitative description of the turbine’s response is
difficult to find. Furthermore the process of binning will introduce an inherent
numeric error. Due to the non-linearity, especially near cut-in and rated
wind speed, the procedure described in the IEC regulation is sensitive to wind
speed variations. These three effects lead to the conclusion that a measured
power curve is influenced by the turbulence distribution at the test site [4].
Therefore, power curve measurements of identical turbines at different locations
will lead to different results. As a consequence measured power curves
have only limited comparable and transferable properties.