OVERVIEW OF A WIND RESOURCE ASSESSMENT CAMPAIGN - Wind Resource Assessment: A Practical Guide to Developing a Wind Project - page 15

Chapters 3-8 provide information and recommendations to support this phase of
the wind resource assessment process. They include guidelines for designing and
carrying out a complete measurement program.

2.2.1 Wind Monitoring Campaign Design
The general objective of a wind monitoring campaign is to obtain the best possible
understanding of the wind resource from the top to the bottom of the turbine rotor
and across the project area, consistent with the project's budget and schedule. This is
achieved by placing meteorological towers and ground-based remote sensing systems
in appropriate locations and obtaining a sufficient amount of data to characterize the
resource. Chapters 3-5 provide guidance in designing a wind monitoring campaign
using tall towers; Chapter 8 discusses remote sensing systems.

Tower Number and Placement. The main goal when deciding how many
towers to install and where they should be placed within the project area is to mini-
mize the uncertainty in the wind resource at potential turbine locations. Meeting this
objective calls not just for monitoring where the wind is strongest but capturing the
full diversity of resources, from the best to the worst, likely to be experienced by the
turbines. The size of the area, topography, land cover, and other factors come into
play in making this decision. Recommendations regarding the number and placement
of meteorological masts are provided in Chapter 3.

Instrument Height. Measuring the wind resource at the turbine hub height (and
preferably through the entire rotor plane), rather than extrapolating measurements from
lower heights, reduces the uncertainty in energy production estimates. The choice
of height depends on a number of factors including project size, tower cost, local
regulations (e.g., aviation-related height restrictions), and knowledge of the site's wind
shear. If the shear is well understood, the value of very tall towers is reduced; on the
other hand, where the shear is difficult to characterize, such towers may be very cost-
effective. For large wind projects ( 100 MW), it is recommended that at least one

in three meteorological towers be of at least hub height. Additional information on
hub-height and taller towers can be found in Chapter 3.

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Tower Instrumentation. The main task of the monitoring program is the col-
lection of accurate wind speed, wind direction, and air temperature data. Wind speed
data are the most important indicator of a site's wind resource. Multiple measurement
heights are needed to determine a site's wind shear. Wind direction frequency infor-
mation is important for optimizing the layout of wind turbines within a wind farm and
for carrying out wind flow and wake modeling. Air temperature measurements provide
additional information about the site conditions and help determine air density.
Recommendations for standard instrumentation packages are discussed in detail
in Chapters 4 and 5. These sections also outline optional additions to the typical
instrument package, which can be implemented if consistent with the project's goals
and budget. These options demonstrate the need for a detailed campaign design that
takes all project variables into account.