Environmental Engineering Reference
In-Depth Information
Applying Equations (2-27), the surface roughness length associated with the Cleveland Water
Intake site is 0.000115 m, which falls within the typical range in Table 8-3 for large expanses
of water: 0.0001 m (calm open sea) to 0.001 m (coastal areas with off-sea winds).
Accurate estimates of the capacity of the wind resource for utility-scale HAWTs depend
on wind data taken at higher elevations, and this is particularly true for offshore sites. As-
sume, for example, that wind speeds at elevations near 100 m are approximately the same
for an onshore and an offshore site. If that is the case, the comparative wind power densities
for these two sites could be as illustrated in Figure 2-23. Because of the lower wind shear at
Figure 2-23. Comparison of calculated vertical proiles of wind power density at on-
shore and offshore sites when higher-level winds are the same at both locations, indicat-
ing a potential advantage in energy production at the offshore site. In this example, the
wind resource is the same at an elevation of 100 m.
the offshore site, wind power densities there at elevations below 100 m may be signiicantly
larger than at onshore sites. This illustrates the potential for increased energy production
from an offshore turbine that may offset to some degree its higher initial capital cost.
Table 2-6 lists the results of calculations of comparative gross annual energy outputs of
utility-scale wind turbines represented by the DOE/NASA Mod-5B 3.2-MW HAWT, fol-
lowing the procedure described in Table 2-2. The potential energy output advantage for the
offshore location is 22 percent in this example.
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