The WAsP Program

WAsP is a program used extensively to estimate wind energy resources. The program can generalise a long-term meteorological data series at a reference site (meteorological stations usually) and may then be used to estimate the wind conditions at a second potential site within certain limits of climate and terrain.
The WAsP Analysis procedure allows to do the data generalisation, which corrects the measured data series taking into account local effects that only affect the reference site.

These local effects are the shelter effects created by close obstacles such as trees, the terrain surface roughness and the orography.

The geostrophic wind conditions are stored in the Atlas file which and then be transferred to the potential site through the reverse process of the WAsP Application procedure (WAsP Analysis) in order to estimate the wind resource of this second site.

Prediction Accuracy

The conditions to fulfill to obtain an accurate predictions using WAsP are that both the reference and predicted sites are clearly:

1. Subject to the same weather regime,
2. The prevailing weather conditions are close to being neutrally stable,
3. Surrounding topography is sufficiently gentle and smooth to ensure that flows stay attached and that large-scale terrain effects such as channeling are minimal.

Of course, the prediction accuracy also depends on the quality of the reference data, the methods used for preliminary data processing and the correct use of the WAsP program.

It has been concluded by many studies that WAsP provides a good estimation of the wind resource provided that the terrain is not too steep. Verifications on different sites have also shown that the predictions from WAsP for wind flows over simple isolated hills was fairly accurate.
However, like other numerical models, WAsP fails to predict the low flow speeds close to the ground on sites where some degree of flow separation is suspected.

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