Q. Does WAsP assume a logarithmic wind speed profile of the atmosphere?
A. Yes – the standard logarithmic wind speed profile is used as a basis in WAsP; however, this profile is modified to take into account the effects of non-neutral stability (controlled by heat flux parameters for land and sea; the stability corrections may be disregarded by setting these parameters to zero) and up-wind roughness changes (the roughness changes experienced by the wind before reaching the point of interest). The actual model for the effect of roughness changes is described in the theory chapters in the European Wind Atlas.
Q. What is the "reference roughness" seen in the site effects page of turbine site and met. station objects?
A. It is the sector-wise reference terrain roughness length used as basis when the effect of terrain features are evaluated. For details, see the page referenced on the FAQ page.
Q. What is the impact of the standard heights in the wind atlas structure on wind climate prediction?
A. The standard heights will influence the small height interpolation errors when making wind climate predictions. When a prediction for a certain location and height above ground level is made, e.g. for a turbine hub height of 80 m, WAsP makes a look-up into the wind atlas table, and if necessary, interpolates between the nearest standard heights. Because of non-linear vertical wind profiles, there will in general be an error in connection with the linear interpolation. Normally this potential error is negligibly small – but it may have to be considered if the distance between the height of the point of interest (hub height) and one of the two relevant standard heights is large.
Example: For a certain turbine with hub height of 80 m, use of standard heights 10, 25, 50, 80 and 200 m a.g.l. prevents height interpolation errors, whereas the default standard heights 10, 25, 50, 100 and 200 m results in a small discrepancy of 1% in wind speed (2% in turbine production). If, however, one chooses 10, 25, 50, 60 and 200 m as standard heights, the unfavorable interpolation range from 60 to 200 m in relation to the 80 m hub height results in a considerably larger discrepancy of 3% in wind speed (6% in turbine production).
It is strongly recommended to keep the standard height of 10 m a.g.l. in any adjusted set-up of the standard heights in WAsP.