Page 151 - Fluid Power Engineering

126 Chapter Seven

WAsP may be used to perform this analysis. The output of the analysis
is wind speed time series data at the desired site and at the desired
height, wind rose (relationship between wind speed and wind direc-
tion derived from wind data), approximation of shear, (based on sur-
face roughness), and estimate of average annual energy production.
This preliminary assessment involves:

1. Analysis of hourly wind speed data available at 10 m height
from local airport
2. Creation of a GIS-based model of the airport site (site A) with
contour elevation and terrain roughness
3. Computation of a generalized RWC from the airport data
4. GIS-based model of site B with modeling of elevation contour,
roughness, and obstacles
5. Translation of the RWC to the desired wind project site
(site B)
6. Customization of RWC to site B.

If no airport data is available, then reanalysis data from NCAR may
be used in place of the airport data in the preliminary assessment
steps described above. Even if airport data is available, NCAR data
may be used to compare wind energy estimates from the airport data
source.
Publicly available met-tower data, within 100 km of site must
not be overlooked. Although it is rare, examples include met-tower
data available from publicly funded wind data collection initiatives
in Iowa, Illinois, Nebraska, and others. Any data source from lower-
height met-towers (with anemometer less than 10 m in height) like
those on highways, bridges, and buoys should be avoided because
lower elevation wind data in greatly influenced by local surface con-
ditions and therefore uncertainty is very high when used to predict
wind speed at hub height.

Onsite Wind Measurement
This was covered in Chapter 6.

Spatial Extrapolation of Wind Resources from Measured
Locations to Planned Wind Turbine Locations
For a single turbine installation, the wind measurement location (site
A) is usually the same as the turbine location (site B). If the two loca-
tions are not the same, then this step is used. For a wind farm, there