Siting - Wind Energy: Renewable Energy and the Environment - page 188

MesoMap: The MesoMap system was developed specifically for near-surface wind forecasting.
It is a modified version of the Mesocale Atmospheric Simulation System (MASS) weather model.
MesoMap uses historical atmospheric data spanning 20 years and a fine grid (typically 1-5 km).
MesoMap simulates sea breezes, mountain winds, low-level jets, changing wind shear due to solar
heating of the earth's surface, the effects of temperature inversions, and other meteorological phe-
nomena. MesoMap does not depend on surface wind measurements although surface measurements
are desirable for calibration.
The model provides descriptive statistics at any height above ground, such as wind speed histo-
grams, Weibull frequency parameters, turbulence and maximum gusts, maps of wind energy poten-
tial within specific geographical regions, and even the annual energy production of wind turbines
at selected sites in the region.
WA sP: Wind Atlas Analysis and Application Program is software developed by Riso National
Laboratory for predicting wind climate and power production from wind turbines. The predictions are
based on wind data measured at stations in the region. The program includes a complex terrain flow
model. WAsP was used for developing the European wind map (see Figure 4.3 ) and is used by many
others across the world. Other models are available, so check the links listed below and the Internet.
9.7 MICROSITING
Wind maps, meteorological data from met towers, models, and other criteria are used for selection
of the wind farm locations. Other considerations for the wind farm developer are the type of terrain
(complex to plains); wind shear; wind direction; spacing of the wind turbines, which then depends
on predominant wind direction and availability and cost of the land; and other items, such as roads,
turbine, and substation. Terrain can be classified as complex, mesas, rolling, and plains. Passes may
be primarily one type or a mixture. In general, spacing is given in terms of the diameter, D, of the
wind turbine, so larger turbines will be farther apart.
As turbines have become larger, are wind shear data from 25 to 50 m sufficient to predict wind
speeds at 70 to 100 m heights? The first answer is yes, for that site, although there is not a definitive
answer at this point if the prediction is for another location in the same region.
In complex terrain, such as mountains and ridges, micrositing is very important, whereas in the
flat plains, the primary consideration is spacing between turbines in a row and spacing between
rows. On mesas, the highest wind speed is on the edge of the mesa facing the predominant wind
direction, so there may be only one row of turbines. In rolling terrain such as hills, the wind turbines
will be placed on the higher elevations.
In California, the high wind classes are due to the hot desert air rising and cooler air from the sea
coming through the passes. There they have the complex terrain at Tehachapi Pass, rolling terrain
of Altamont Pass (east of San Francisco), and both ridges and flat terrain at San Gorgonia Pass near
Palm Springs. The winds in the passes are predominantly from the west, so the rows are primarily
north-south. At San Gorgonia Pass some wind turbines were only 2D apart in the rows, and then 4D
to 5D between rows because of the high cost for leasing the land for wind farms. With tight spac-
ing, turbines could also be placed at different heights. As expected, the array losses are fairly large.
Starting in 1998, the smaller-size turbines were being replaced with larger turbines.
The wind farm near White Deer, Texas, has eighty 1 MW wind turbines, which are 56 m diam-
eter. The wind turbines have a spacing of 4D within the row and 8D between rows ( Figure 9.11 ) .
North is at the top of the figure, and the lines indicate roads at 1 mile (1.6 km). Notice the buffer
zone on the west, as that land was not under lease to the wind farm. Predominant winds are south-
southwest during the spring and summer, and from the north in winter. As lower winds are in July
and August, rows are situated perpendicular to those predominant winds. There are low spots due to
playa lakes (only contain water after rain), so there are no wind turbines in those locations. Only the
west side of the wind farm is visible in the photo, as there are more turbines to the east. Examples