Wind resources at Horns Rev

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energy. environment. knowledge. Page 34 of 69 Figure 3.6 example of measured 3-D time series 4. Updating resource estimates It is well-known that short-term measurements do not capture the full-range of variability of wind speeds at a site. The aim of this section is to use different methods to assess the wind resource at the offshore measurement site based on long-term (climatological) data sets. The purpose of using different methods is that each methodology has different strengths and weaknesses and by comparing the results the uncertainty of the analysis can be estimated. 4.1 Characterising the long-term climate at Horns Rev Data from the offshore meteorological mast at Horns Rev are compared with those from the land-based meteorological station at Hvide Sande. Since data are available from Hvide Sande covering the period 1989 to 2002, the measurements at the site capture the long-term variability of wind speeds in western Denmark. By establishing a relationship between the data at the offshore site and the land-based Hvide Sande site for the period Report no.: D-160949 Tech-wise A/S is an international consulting Tech-wise A/S engineering company specialised Kraftværksvej 53 in energy and environment DK-7000 Fredericia
energy. environment. knowledge. Page 35 of 69 of simultaneous measurements (May 1999 to October 2002), data from the offshore site can be corrected to allow for the fact that the climate during the period of measurement may differ from the climate from a long-term perspective. An approximate value for the mean wind speed at Horns Rev can be obtained using a straightforward comparison of the two periods. The mean long-term wind speed at a height of 27.5 m at Hvide Sande is 7.14 m/s, but with 6.91 m/s 3.2% lower during the overlap period. It is therefore to be expected that the mean wind speeds at Horns Rev are approximately 3.2% higher than the 9.49 m/s measured during the overlap period, i.e. approx. 9.79 m/s. In the following sections, the methodologies used in the previous analysis are employed to update the wind resource estimates for Horns Rev. These results are then compared with those conducted in previous correlation analyses performed by Tech-wise and Risoe. It should be noted that mast shadow corrections have not been used to correct neither the Horns Rev data nor the long-term data set from Hvide Sande for the following reasons: 1. To retain comparability with previous analyses. 2. All wind resource estimates are performed based on the wind speeds from the top anemometer, which is expected to exhibit the least mast shadow effects in the record. 3. Because it is not possible to correct data from Hvide Sande. 4.2 Resource estimates using different methodologies Different methodologies are employed to reduce the uncertainties of the predicted wind speeds. However, the Weibull correction and measure-correlate-predict (MCP) methods do not account for the differences in directional distribution between predictor and predictand sites. 4.2.1 Weibull method The Weibull correction method for extrapolating wind speed data series is based on the concept of modifying the Weibull parameters to characterise a longer data sampling period (as described in section 4.1). The method was developed and described in[4], but in brief is employed as follows: Report no.: D-160949 Tech-wise A/S is an international consulting Tech-wise A/S engineering company specialised Kraftværksvej 53 in energy and environment DK-7000 Fredericia
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Wind resources at Horns Rev

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