Hi Peter, wind is more affected in altitude, so the effect at around 100 m of a large wind farm will be sensible several miles away (however 30% is surprising). Close to ground level the situation is different because the wind is slower and less steady anyway. It all depends on roughness between the farm and the spot. If plenty of trees, buildings, hills... the difference will be negligible. If very flat land or open water like Rodsand, the extra turbulence will travel much longer. http://www.talentfactory.dk/en/tour/...lter/index.htm
for speed simulations and http://www.talentfactory.dk/en/tour/wres/park.htm
for park effect.