Petros

Hello Duncan and Rae, What made me reduce the size (surface) of the map was the results that i would get and not the speed of calculations. Duncan if you mean the resource grid area, then i would agree that the extent of the grid affects the calculation time, but when it comes to Wind Farm calculations the calculation time is insignificant. I just found out that there were only minor changes on the results while i expected higher discrepancy. Roughness lines did not change when i changed the height contour map, and were covering the same area (10km away from the WTGs)as in the primary condition. The height contour intervals did not change (20m). Now for high complex terrain sites (which is the rule in Greece) i don't really see that even in closer distances (3-5km from WTGs) roughness can affect dramatically the results. When the slopes are 40,50% or even higher i suppose that turbulence causes high mixture of the air, so roughness is much less significant than it would be in a flat terrain site.

Dear WAsP team, Recently i received some past WAsP projects done with some really small sized maps. This triggered my curiosity to see how small sized maps affect the results on WAsP. What i did was that i clipped a map of a recent project, that was primarily cut according to WAsP best practices (minimum distance between the WTGs and the borders about 5km), to a smaller area where distance between the WTGs and the borders was not bigger than 1,5km. The results where really close on all variables (AEP, wind speed, wake losses). Net AEP difference 0,5%. So my question is, why should we have larger digital maps (meaning extra cost) when we get almost the same results with much smaller ones? Is there any rule (apart from the 5km one) or any explanation how the map affects the calculations? I am talking about complex terrain sites, with varying roughness. Thank you in advance Petros

Hi Troen, Thank you for your input. Your answer is actually what I expected, but i also have one more question. When a forest is located in a flat area the trunks of the trees are usually perpendicular to the ground, but when we are on the slopes this changes since the trees grow vertically to the horizon so this decreases the effective height of them. The roughness length of a 15m high forest should not be the same in a flat terrain and a slope with lets say 30 degrees because then we have 13m high forest. Is this change taken into account? Appart from the roughness length this would influence the IBL (internal boundary layer) too.

Dear WAsP team, I am currently working on a project in Greece on a very mountainous area. Additional to the slopes, the windfarm lies very close to a fir forest which ends about 80m from the ridge where a 10m high mast is installed. As a result we have a Roughness Class 2.5 area really close the the mast position. Generally the hill ridge is clear so most of the turbines and the mast are found in a roughness class 1 area. What WAsP returned as a result is a small negative wind profile since wind speed at 80m is calculated slightly lower than the one measured at the mast height. Also the energy density seems to be relatively low to what we expected. I was trying to find some explanation by myself and what is more convincing to me is that due to the clearing there is a speed up at the lower levels which cannot be applied at 80m due to the small distance between the forest and the mast. But as i was trying to find a more scientific answer it turned out that the model of roughness that WAsP uses does not contain any information on vertical displacement due to orography. My question is: Does WAsP calculate the roughness effect on a flat terrain and the ads/subtacts the results from the speed up due to orography? Does the roughness model take into account the complex terrain? Should i add any displacement height as mentioned in Dellwik's paper on forests and WAsP if i am located in a complex terrain site? Any input would be welcome Thanks in advance Petros

Dear WAsP Team, I am doing some validation of a project that i run on WAsP. This project is located in southern Greece and in a complex terrain site. After calculating the wind atlas i added a reference site at the location of the meteo mast and at the same measurement height. The results from the reference site calculation differ about 12% at the same height. Is that normal, since we don't have any horizontal displacement? Thank you in advance Petros