Wind speed data (10-07-2015)
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    Asked by 805 days ago Answers (1)

    The wind speeds found by Ecofys (in the wind resource assessment) differ from the wind speeds found by Deltares (in the metocean study). What are the reasons for the differences and does this have consequences for the studies which are already published?

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        • Public 805 days ago

        As stated in section 3.4.3 of the Ecofys wind resource assessment, these differences are related to the use of the Harmonie model by KNMI. The adjustments made by KNMI can be read in Section 1.1.3 of Validation of KNW atlas with publicly available mast observations (Phase 3 of KNW project) ( There one can read that “Geertsema (2014) concluded that the model underestimates the vertical wind shear by a factor of about 15% which implies that the wind at a 100 m height is underestimated by about 5%”.  The applied correction for wind speed is –depending on the roughness- about -2% (overestimation) at 10 m to +5% (underestimation) at 100 m.

        Waves and water levels are a function of the drag at the surface and related to the 10-m wind speed. This function is –about- linear to quadratic. This implies that a variation of a% in the wind speed will result in a variation ranging from a% to 2a% in the wave heights and the water levels. Therefore, an overestimation of 2% of the 10-m wind speed means that the waves and water levels are overestimated by at most 4%. Such differences are within the uncertainty ranges given in the Metocean report and the Wind Resource Assessment.

        Differences between the studies are within uncertainty ranges and can be explained, therefore, there is no need to update the already published Metocean report(s).