The Illusion of Power Curves: Understanding TI, Shear, and Atmospheric Stability in Power Performance

Power curves are a fundamental element of any wind resource assessment. These are required to estimate how much energy a wind turbine will convert. The theoretical power curves are validated with measurements in test sites, however they may not be fully applicable in different wind climates as they are dependent on the site where, and the weather conditions when they were measured. The turbulence, and wind shear, connected to the atmospheric stability, are phenomena related to significant deviations in the power output expected from the power curves. They affect the energy available in the profile for conversion, and the actual conversion efficiency of the wind turbine. With actual data, distinguishing these changes is challenging, through simulations these factors could, however be relatively told apart from each other. The present work addressed the research question how these factors influence the estimation of power curves and investigated the methods to account for them in order to ultimately deliver more reliable power curves. Data from a flat, smooth, uniform test site in the Nether- lands and from a medium complexity site in Sweden was segregated by atmospheric stability, turbulence intensity, and shear, to generate regime-, turbulence-, and shear-dependent power curves to compare. The impact of these factors was observed, and it could be only till a certain degree accounted for. Bladed simulations were also employed to study the isolated effects of turbulence and shear; their influence in the power output was analysed and better results accounting for shear were achieved, turbulence for shear-less profiles was successfully accounted for with the proposal of a mixed correction. A correlation between the energy in the profile and the power output was found for the cases of shear and turbulence intensity. The concept of equivalent wind speed for wind resource assessment was analysed and the use of visualisation from LiDAR data to further understand the shear, TI, and stability at a test site was effectively explored as well. A series of recommendations for power performance are formulated.

Subject

Windenergy
Power performance
power curves
atmospheric stability
atmospheric conditions
turbulence intensity
vertical wind shear
equivalent wind speed
wind resource assessment
wind turbine certification
LiDAR
dynamically generated power curves
power production loadings

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Student theses

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master thesis

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Hector Villanueva r.pdf

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