Environmental Engineering Reference
In-Depth Information
most offer the benefit of being compatible with GIS. Since the 1990s, there has been
an explosion in the availability of regional wind resource maps. Some regions, such
as North America and parts of Europe, have been mapped multiple times by different
companies and groups using a variety of methods (Fig. 3-1). Some sources of wind
resource maps are listed in Appendix B.
However, regional resource maps must be used with caution, as their accuracy and
spatial resolution vary widely. Some maps provide little more than general guidance
about the wind resource in a region (and may be based on questionable methods and
data), while others may offer sufficient accuracy and detail to be used for preliminary
site selection and plant design. It is important for the analyst to investigate the methods
and data used in creating a particular map and to determine whether it has been
compared against independent, high quality wind measurements and, if so, the error
margins obtained.
The types of information presented in wind resource maps also vary. Some maps
indicate the estimated long-term mean wind speed, while others indicate the expected
mean wind power density in watts per square meter of swept rotor area. Neither
parameter can be translated directly into production by a wind turbine, which depends
also on other factors such as the speed frequency distribution and air density, as well
as on the specific turbine model and hub height. Some wind map vendors provide
such supplemental information on request, including estimates of capacity factor for
particular turbine models.
Even the best regional wind resource maps are usually not accurate enough to
replace on-site measurements, although exceptions can sometimes be made for small
wind projects where the added precision of on-site measurements does not justify the
cost of a wind monitoring campaign. Quoted uncertainties in the mean speed typically
fall in the range of several tenths to one meter per second or more, and the spatial
resolution ranges from 100 m to 5 km. Confidence in the maps is usually greatest
in relatively simple terrain and where ample validation data provided by high quality
measurements exist. A greater uncertainty can be expected in complex terrain and in
data-sparse regions.
3.2.2 Wind Measurements
Publicly available wind data can be useful for assessing the wind resource in a region,
especially if the wind monitoring stations are in locations that are representative of
sites of interest for wind projects. An example would be a tower on a ridge line
that runs parallel to a similar ridge under consideration. Tall towers instrumented
specifically for wind energy assessment are greatly preferred, but airports and other
weather stations can provide a helpful indication of the wind resource as well. It is
important in all cases to obtain as much information as possible about each station to
determine whether or not the data are reliable. Several elements should be considered
in this determination:
station location
•
tower type and dimensions
•
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