Wind Resource - Wind Energy: Renewable Energy and the Environment - page 51

4 Wind Resource
There are two aspects of wind resource assessment: (1) determination of the general wind power
potential and (2) determination of wind power potential and predicted energy production for wind
farms. Wind resource assessment for wind farms will be covered in the chapter on siting.
The general wind power potential was determined from the wind speed data available, and then
wind maps were developed. In general, the wind speed data that were available were at heights of 6
to 20 m; however, some anemometers were on top of buildings or control towers at airports, which
influences the accuracy of the data. In many parts of the world the amount of wind speed data was
limited to daily or even monthly averages. Wind classes were developed for 10 m height, because
that was the standard for world meteorological data, and then the wind power potential at 50 m was
double that at 10 m due to the assumption that the wind shear exponent was 1/7 for all locations.
A world wind map was prepared by Pacific Northwest Laboratory using wind data compiled
in 1980 [1]. The assessment was made by critically analyzing all available wind data and previous
assessments in order to estimate the broad-scale distribution of wind power potential. Much of the
data were used cautiously because of the lack of information on anemometer height and exposure.
Global pressure and wind patterns, upper air wind data, and boundary layer meteorology were
also used to obtain a consistent estimate of the wind energy resource. Where an actual wind speed
frequency distribution was available, that was used, or a Weibull distribution was used, to esti-
mate the wind power potential. If only mean wind speeds were available, a Rayleigh distribution
was used.
Most of the general results were known; for example, there are strong trade winds, northeast in
the northern hemisphere and southeast in the southern hemisphere. At mid-latitudes (about 40-60°)
the flow is westerly, and strong westerlies circle the world all year round in the southern hemisphere,
which results in very strong winds at the tip of South America, southwest coast of South Africa,
southern coast of Australia, Island of Tasmania, and New Zealand. The flow of the westerlies in
the northern hemisphere is broken up by the large land masses. The region off the northern coast of
South America also shows high wind speeds. The wind around the poles is predominantly easterly.
The world wind map is available online [2] showing wind class at 50 m height for typical open,
well-exposed sites. This is a very broad map and should be viewed with caution in estimating wind
power potential. Country, state, and regional maps, formulated from better data and with much
higher resolution, are now available for many parts of the world.
Note: If you are searching the Internet for world winds, links referring to NASA World Wind are
for open-source Windows software to view satellite images of the earth and do not have anything to
do with world wind maps or estimations of world wind power potential.
Archer and Jacobson [3] quantified the world's wind speeds, which are an indication of wind
power potential, at 80 m height for the year 2000. A least square extrapolation technique was used
to estimate wind speeds at 80 m from observed wind speeds at 10 m and a network of sounding
stations. Globally, ~13% of the stations have class 3 (mean wind speeds ≥ 6.9 m/s) and above winds
at 80 m, regions that are suitable for wind farms. This is a conservative estimate; for example,
India does not show any winds above class 2, and it has a number of wind farms. Wind maps are
presented for Europe, North America, Australia and New Zealand, Asia, and Africa. In general, the
maps show the same regions of high winds as the previous world wind map. The major difference
is that each met station is classified by a dot indicating the wind class. Again, these maps should
be used with caution, as mean wind speeds are just an indicator of wind power potential, and mean
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