Page 97 - Fluid Power Engineering

CHAPTER6

Wind Measurement

What we observe is not nature itself, but nature exposed to our method
of questioning.
—Heisenberg, Physics and Philosophy, 1963

Introduction
As described in Chapter 2, wind energy production is a cubic func-
tion of wind speed. This implies that small changes in wind speed esti-
mates can result in large changes in wind energy estimates. Therefore,
a lot of emphasis is placed on wind speed measurement because this
translates to higher accuracy in estimation of a project’s financial re-
turns. In the beginning of this chapter, the various properties of wind
speed are discussed followed by detailed description of how wind
speed and direction are measured. The following section presents
the uncertainty associated with instruments used for measurement of
wind speed. The next section describes design of a measurement cam-
paign, followed by data management and reporting. The last section
briefly describes use of remote sensing to measure wind condition.

Definition of Wind Speed
Although definition of wind speed may seem trivial, in reality, it is
not. This exposition on wind speed will cover facets of wind speed
that are relevant from the perspective of a wind energy project.

Wind velocity in the horizontal plane. From the perspective of a

wind energy project, the two quantities of importance are the
resultant wind speed in the horizontal plane and the direction
in the same plane. Vertical axis wind turbine (VAWT) captures
energy irrespective of the direction of wind in the horizon-
tal plane. Horizontal axis wind turbine (HAWT) has a yaw

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