Cross prediction

Performing cross prediction is a powerful way of utilizing wind data from on-site wind measurement masts.

As WAsP does not allow more than one met. station to define a Generalised Wind Climate (GWC or Wind Atlas), we recommend to utilize sets of wind data from different masts to validate the wind resource modelling over a site, typically a candidate site for a wind farm. This can be done by a systematic set of comparative predictions called a cross prediction. How to perform such a procedure is indicated in the scheme below, for the case of 3 met. masts on a site:

You start by using the M1 wind data to calculate an RWC and then use that to perform predictions for the wind climate at M1 itself and at M2 and M3; and then continue the same way, now using M2 and M3 as the predicting mast, respectively.

Please note the self-predictions with the green background − the deviations here from measurements are simply due to the limited resolution (speed and direction) when analyzing the time-series of measured wind.

The agreement between the off-diagonal predictions (i.e. excluding self predictions) and measurements is a measure of how well the wind resource is modelled over the site in question.

Optionally, one may adjust relevant modelling parameters within reasonable limits to optimize this agreement. The modelling parameters to adjust could e.g. be:

• terrain descriptions (e.g. roughness values in digital map or roughness roses), and

• heat flux values used to evaluate stability effects (project modelling parameters

Even after the above mentioned adjustments it may be necessary to interpolate between the resulting RWCs. Interpolation between two or three RWCs may be performed by the LIBINT software contained in the WAsP Utility Programs Package (see Interpolation of wind atlas data sets).