Ib

Dear Rameshmuthya Its always best to have measurements and application sites close - both in terms of setting (coastal, flat terrain, complex , etc) and distance (the WAsP "similarity principle"). However, WAsP is designed to estimate e.g. AEP at points many kilometers away from a measurement site. In this context 15km well within the "norm". The key question is whether the overall wind climate is governed by large scale forcing (in which case your two sites should experience close to the same forcing except for the terrain modification, which WAsP will take care of for you) or more dominated by very local flows (e.g. if you were in a narrow valley, then your distance of WAsP application could be very limited)... In your case of Gujarat, with hundreds of kilometers of plains and presumably the wind climate dominated (at Wind power relevant speeds) by large scale systems (the monsoons) (?) you should be ok within several tens of kilometers. To give a more accurate answer to your second question (as you can see very connected to the first one) one will need to do a study of Gujarat wind climatology either by studying - possibly modelling with mesoscale model -the meteorology or by looking at WAsP cross predictions between good measurement sites with reasonable length (years) good quality at different locations if they exist. Best wishes Ib WAsP team

Hello Bas WAsP does not use a "blending height". The term "blending height" was first (I think) introduced by Wieringa (1986) - at that time at the KNMI. He used the concept for matching of log profiles in the analysis of gustiness over inhomogeneous (flat) terrain. He, and later others, uses the concept to arrive at an estimate of an "effective" roughness over some area made up of patches of various roughnesses. Wieringa indeed found that his data was best represented if the blending height was set to a fixed value of 60m. Others have introduced blending heights depending on horizontal scale of the patches. For non neutral atmospheric stabilities some workers have found that the blending height concept may break down (requiring large unphysical values)... WAsP uses a different methodology for analysis of inhomogeneous terrain - involving several steps: 1) Analysis of input roughness contour lines (in map file) to give averaged roughnesses per direction sector as function of distance 2) Fitting of the sectorwise roughness variations to piecewise constant values, setting (up to ten) steps at distances where most significant changes occur 3) Using the theory of "internal boundary layers" (originating at each roughness step) to calculate the ratio of windspeed at the considered point (x,y,z) to the concurrent far upstream windspeed (beyond all roughness change steps)at the same z. 4) Using these ratios, together with the "far upstream" roughnesses ("mesoroughness") estimated under 2 and 3 to relate to the "geostrophic wind" via the "geostrophic darg law". (Which is slightly more complicated than a vertical extrapolation along a log profile) 5) Relating from geostrophic to "standard" homogeneous conditions using the geostrophic draglaw (assuming same geostrophic wind from 4) in reverse. 6) Introducing stability effects (not accounted for in the above steps) via a statistical model derived from surface layer theory and the geostrophic draglaw of how wind profiles deviate when surface fluxes are not zero (neutral). ... Details can be found in the European Wind Atlas (Troen and Petersen 1989) ... Thus depending on how you estimate a blending height you may get varying results and possibly seemingly "unphysical" - as WAsP does not use the concept explicitly. Best wishes Ib

Hi Petros From what you describe a negative wind shear is quite plausible (as predicted by WAsP). The 80m clearing from the edge of the forest to the 10m mast should have very little if any effect at 10m. It is true that the roughness change model in WAsP gives same results (for a given roughness configuration) for flat or non-flat terrain (The orographic model does however take local variations of roughness into account). Apart from the fact that the orographic model results depend on the roughness, the two models for roughness and orography are giving independent correction factors which are added in WAsP. WAsP does not pt consider displacement. Regarding displacement adding/subtracting: This complication should be treated the same way in complex and flat terrain. For your configuration, dependent on the density and height of the forest, you can expect some effects and it would be a good idea to try to estimate these. Good luck Ib Ib Troen