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Wasp and uncertainty (2003-11-13)

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Dear all,

Some of the external consultants I met in the field of wind resource assessments require that the wind measurement mast is at least 2/3 as high as the forecasted hub height. Which means for 80 meters WTG, a minimum height of 54 meters. In terms of costs, this requirement has huge impact.

Among the reasons evoked for such a requirement, it is always mentioned that the more the distance between hub and mast heights is great, the more inaccurate the height extrapolation of WAsp will be. Thus, in case of great difference, the uncertainty of Wasp calculations will be increased. I fully understand that point, but I have to find the good compromise between accuracy and costs of measurement campaigns.

My questions are : for the specific point of hub height (with regards with hub height), does Risoe has any recommendations, and if yes how were they issued (case study available?). More generally, I guess that the uncertainty on Wasp calculations depends on this difference of height between measures and hub but also on terrain (orography, especially). Do you have any study on this uncertainty induced by Wasp calculations according to the type of terrain, height extrapolation and other sources of error (I do not mention the uncertainties of measurement/calibration/roughness and orography digitization/power curves ... which are independent) ?

Thanks a lot in advance


Dear Vincent (and all)

In last EWEC'03 conference in Madrid, we presented the results of a wind profile comparisons among 3 SODARs, 2 WAsP extrapolations and a 100m-high met tower measurements over flat terrain.

One of the conclusions of that project was that, for that limited set of experimental data, WAsP discrepances relative to tower measurements at 100m could range between 10% and 30% (in terms of AEP) depending of the stability parameters used when extrapolating from 30m measures.

Best Regards
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