Wind Speed Measurement in Practice
Amemometer Mast The best way of measuring wind speeds at a prospective wind turbine site is to fit an anemometer to the top of a mast which has the same height as the expected hub height of the wind turbine to be used. This way one avoids the uncertainty involved in recalculating the wind speeds to a different height.
By fitting the anemometer to the top of the mast one minimises the disturbances of airflows from the mast itself. If anemometers are placed on the side of the mast it is essential to place them in the prevailing wind direction in order to minimise the wind shade from the tower.
Which Tower?
Guyed, thin cylindrical poles are normally preferred over lattice towers for fitting wind measurement devices in order to limit the wind shade from the tower.
The poles come as kits which are easily assembled, and you can install such a mast for wind measurements at (future) turbine hub height without a crane.
Anemometer, pole and data logger (mentioned below) will usually cost somewhere around 5,000 USD.
NRG data logger
NRG data logger Photograph by Soren Krohn
© 1998 DWIA
Data Logging
The data on both wind speeds and wind directions from the anemometer(s) are collected on electronic chips on a small computer, a data logger, which may be battery operated for a long period.
An example of such a data logger is shown to the left. Once a month or so you may need to go to the logger to collect the chips and replace them with blank chips for the next month's data. (Be warned: The most common mistake by people doing wind measurements is to mix up the chips and bring the blank ones back!)
Arctic Conditions
If there is much freezing rain in the area, or frost from clouds in mountains, you may need a heated anemometer, which requires an electrical grid connection to run the heater.
10 Minute Averages
Wind speeds are usually measured as 10 minute averages, in order to be compatible with most standard software (and literature on the subject). The result for wind speeds are different, if you use different periods for averaging, as we'll see later.
© Copyright 1997-2003 Danish Wind Industry Association
Updated 19 September 2003
http://www.windpower.org/en/tour/wres/wndsprac.htm
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