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Wind speed at hub height calculator.
Wind is faster higher up. Scale a measurement to tower height and see how much more power it brings.
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Hub-height wind
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How do you find wind speed at hub height?
The wind shear power law scales a speed measured at one height to another: v2 = v1 x (h2 / h1)a, where a is the wind shear exponent. A 2000 note in Wind Engineering reports 0.14 as the typical value, though it is often picked fairly arbitrarily, so measure it where you can. DOE's Small Wind Guidebook says calculating the exponent requires data at two different heights; with two measurements a = ln(v2 / v1) / ln(h2 / h1). DOE also says average speeds may be 15% to 25% greater at a typical hub height than at airport anemometer height, and that power depends on the cube of speed. For siting, DOE recommends the bottom of the rotor be at least 30 ft (9 m) above any obstacle.
Worked example. 5 m/s measured at 10 m, hub at 30 m, a = 0.14: 5 x 30.14 = 5.83 m/s, 17% faster, which is 1.173 = 1.59 times the power. With a 12 m tree and a 1.5 m rotor radius the blade tip bottom must be at least 21 m and the hub at least 22.5 m.
Frequently asked questions
How does wind speed change with height?
It generally increases. DOE says average speeds may be 15% to 25% greater at a typical hub height than at airport anemometer height. The power law v2 = v1 x (h2/h1)^a estimates the exact change.
What wind shear exponent should I use?
0.14 is the typical value reported in the literature, but real values vary with terrain, trees and weather. Measuring at two heights gives your site's own exponent.
How high should a wind turbine tower be?
DOE says the bottom of the rotor blades should be at least 30 ft (9 m) above any obstacle. Taller is usually better because speed rises with height and turbulence falls.
Does a bit more wind speed really matter?
Yes. Power scales with the cube of wind speed, so a 17% faster wind gives about 59% more power.
Sources
Checked
- U.S. Department of Energy WINDExchange: Small Wind Guidebook
- Wind Engineering 24(1), 2000: wind speed with height exponent estimation
The 15% to 25% height gain, the 30 ft clearance and the cube relationship are from the DOE Small Wind Guidebook. The 0.14 exponent is the typical value from the Wind Engineering note and varies with terrain. Runs entirely in your browser. Nothing you type is sent or stored.
Scope
Planning estimate only. Site wind varies with terrain and turbulence; measure at your site and get a professional assessment before installing a tower.