High shear (different wind speeds at different heights) creates problems with power curves.
A 2.3 MW with 82.4 m rotor and 60 m hub height has 3.5% less apparent power at 10 m/s if sited near a 20 m forest with m = 0.25 than if sited in open terrain with m = 0.14 (where m is shear).
Bonus uses following rules of thumb for evaluation of possibility of power curve measurement:
- Shear not to exceed 0.20
- This shear expected possible if tree height does not exceed a horizontal level of:
- Hub height − 0.67 rotor diameter for distance from trees less than 5 rotor diameters; up to
- Hub height − 0.50 rotor diameter for distance from trees equal to 10 rotor diameters
Presentation by Bo Schou Nielsen and Henrik Stiesdal, Bonus Energy (now Siemens), 17 March, 2004
Download original document: “Trees, Forests and Wind Turbines – A Manufacturer’s View”
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