It is essential to measure the wind speed as near to the hub height of the proposed turbine as possible. If ‘best practice’ of a hub height mast is not followed, then a reasonable compromise is to ensure that masts are no less than 75% of the hub height of the turbine. If wind measurement at or close to hub height is not made then it will be necessary to estimate the shear profile. This is possible, but it creates much higher uncertainties which may not be acceptable for some projects.
Source; GL Garrad Hassan
For 30m hub turbines in Northern Ireland we would strongly advise hub height wind monitoring. From our own wind monitoring stations, we have found a wide range of variations in wind speed at 15m – 20m measuring points from site to site which could have led to inaccurate predictions had there not been a further measuring point at 30m to provide exact figures.
For hub heights of 30m and 40m measurement at a minimum of 30m is the only way to ensure a high level of accuracy.