Wind resources at Horns Rev

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energy. environment. knowledge. Page 14 of 69 All spikes (>4×σ) are identified by means of a screening procedure and inspected afterwards, but only significant spikes are marked with a code = 2. The second condition (2) could result in code = 3, which indicates a signal drop to zero. This procedure is only applicable for wind speed signals, while it is based on both maximum and minimum values. 1.3.2 Determination of signal drop-outs 1) The wind speed signal drop-out is determined as a period with low (= zero signal) values corresponding to the minimum signal reading (< 0.1 m/s). 2) Furthermore, periods with low signal activity (σ
energy. environment. knowledge. Page 15 of 69 1.4 Data overview The data coverage rate for the measurement systems is shown in the table below. Table 1.3 Data coverage rate for the meteorological measurement systems. Measuring system Data period Hours Data coverage Primary met. system Back-up met system Sonic System May 1999–Nov. 2002 May 1999–Nov 2002 October 1999–Nov. 2002 1.4.1 Directional sensitivity analysis 30638 30359 26888 99.05% 87.99% 37.35% The directional sensitivity has been investigated for wind vanes mounted at three different heights (28, 43 and 60 m above DNN) and is based on more than 21,000 hours of measurements recorded in the wind speed range (5–25) m/s. The reference height is 60 m and the bin-averaged differences (bin size =2°) are shown on Figure 1.7-a. The maximum absolute difference is measured in the northern direction and decreases towards the south. All three vanes are free of wake effects in the VSV sector (258 ±90°), although they do not agree very well (+2/-3°) even in this sector. The best agreement has been obtained for 180° ±35°. This analysis recommends that the wind direction measured at height 60 m be used, and not to merge directional measurements from the other levels. The uncertainty of the absolute directional measurement is ±4°. Figure 1.7-b shows that the mast wake dominates the measurements in direction 20–45°, corresponding to a boom direction of 212°. The average standard deviation of the wind direction measurement is approx. 4° - in free, undisturbed winds. 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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