PLANT DESIGN AND ENERGY PRODUCTION ESTIMATION - Wind Resource Assessment: A Practical Guide to Developing a Wind Project - page 253

500

400

Free-
stream
profile

300

Disturbed
profile

200

100

0

0 500 1000 1500 2000 2500 3000

Distance downstream of roughness change (m)

3500 4000 4500 5000 5.5 6.5 7.5 8.5 9.5

Wind speed (m/s)

Figure 16-9. Illustration of the growth of two IBLs created by the wind turbine at left, which
is modeled as a surface roughness change. Between the top and bottom curves, the wind shear
is determined by the high roughness of the turbine; above the top curve and below the bottom
curve, it reverts to the shear associated with the background roughness. The two curves on
the right illustrate the effect of this turbine on the free-stream wind speed profile at the fourth
turbine, 3000 m directly downwind of the first. Additional turbines (not shown) would create
their own IBLs and further modify the profile in an analogous fashion. The curves are examples
only and are not intended to represent any particular model or plant. Source: AWS Truepower.

16.8 QUESTIONS FOR DISCUSSION

1. Suppose the windiest point in a wind project site has a mean wind speed of
8.6 m/s and an estimated annual average air density of 1.125 kg/m 3 . The mean
turbulence intensity at 15 m/s is 15%. What turbine suitability class would be
appropriate for this site? Using the Internet, find three commercial megawatt-
class turbines in this class and list their main characteristics (rated capacity,
rotor diameter, hub height).
2. Consider the topographic map in Figure 16-2. Identify the stranded turbines in
this layout, and explain why they are likely to be more costly to build than other
turbines in the layout.
3. Consider the set of power curves in Figure 16-5. Suppose you are only given the
power curve for an air density of 1.225 kg/m 3 (last column on the right). Assume
that the estimated air density at your site is 1.14 kg/m 3 . Using Equation 16.1,
calculate a new power curve for the site, and then compare it with the true power
curve for the same air density from the table. What is the maximum difference at
any given speed? Do you think this is a reasonable approximation? (Procedure
for calculating the power curve: adjust the standard speeds for the existing power
curve according to Equation 16.1, interpolate the power at 1.225 kg/m 3 to the
adjusted speeds, and assign the new power values to the original, unadjusted
speeds.)