resources grid difference results

[malik]

I am using wind observation data at an altitude of 30 meters to calculate resources grid at a height of 50 meters. why the huge difference in the results (approximately 7.7%) compared to the results of resources grid if using wind observation data at height 50 meters?

[Niels Gylling Mortensen]

Assuming that you use the same map for the two calculations, it follows that the difference is caused by the two different wind atlases used. And, if you predict one anemometer with the other, and vice versa, you will therefore get similar differences. This difference may be caused by a number of things:
1) are you using the same period of data for the two anemometers?
2) are the two anemometers of the same type and age?
3) are the two anemometers calibrated in the same way?
4) are the mast flow distortion effects similar for the two anemometers?


If you can say 'yes' to these questions, it seems that WAsP cannot model the vertical wind profile well, given your topographical inputs. So, you could try to adjust these, especially the roughness description, in order to improve the vertical wind profile modelling. Of course, the roughnesses should still be realistic, after you have changed them. You should also check the elevation map (see the WAsP Best Practices), is it detailed enough close to the mast?


If this is still not enough, the wind profile can also be tweaked by changing the heat flux values of the project, but you should be careful doing this - and the values should make sense (where in the world is the project?).


Of course, the 50-m anemometer will give the most reliable 50-m predictions - all other things being equal. So, you should probably trust this result more than the results from the 30-m anemometer.