Problem with Wind Atlas Structure modification...

[Ellsworth Morriss]

Hi,
when the wind atlas structure is modified using Project Configuration, the re-calculated AEP changes appreciably !
In my mind, the wind atlas structure, as a wind atlas representation, must not change the results.
Is this problem known ?
Is that a bug ?


Thank you for any help.

[Niels Gylling Mortensen]

In an ideal world, the wind atlas shouldn't change the results, because it would then contain a very comprehensive and detailed description of the generalised wind climate that drives the predictions. However, with only 5 heights and 5 roughness classes, this is not so...


It has always been the case that the wind atlas configuration should span and represent the conditions you want to model. So, the data and prediction sites should be within the ranges of height and roughness length in the atlas, and the configuration should be changed to best represent the modelling scenario. For years, most users didn't bother to change this, though.


Recently, we have stressed this aspect of the modelling more, not least because modern wind turbines often have a hub height between the two standard heights of 50 and 100 m a.g.l.


So, it's a known issue (it's not a bug) and we do recommend to change the configuration. In most cases, the changes in the results are quite small, on the order of one per cent. Do you see bigger changes?


PS. This may well be changed in a future version of WAsP.