Environmental Engineering Reference
In-Depth Information
be acceptable in some cases to install a tower with just two levels of anemometers,
rarely just one. It may be fine to use a new or unusual atmospheric model, but not
without anchoring the results in reliable measurements or testing the model's accuracy.
What we hope the reader gains from this topic is a clear understanding of those limits.
Whenever possible, the topic goes beyond a cookbook to describe some of the
concepts and principles behind the tried-and-true techniques. This, we hope, will
empower the reader to make his or her own judgments where conditions depart, as
they often do, from the ideal. What the topic does not strive to be is a comprehensive
reference on every aspect of wind resource assessment. For those many interesting
topics, there are standards published by the International Electrotechnical Commission
(IEC), proceedings of the many wind conferences that occur every year around the
world, and a number of topics and Internet-based resources.
The topic is organized in the order of the main stages of wind resource assess-
ment. The first several chapters focus on the nuts and bolts of conducting a wind
measurement campaign. It starts with an overview of the wind resource assessment
process. Then it moves through site selection, measurement parameters and tower
instrumentation, tower installation and maintenance, and data collection and han-
dling. The last chapter in this group, Chapter 8, focuses on remote sensing (lidar and
sodar).
The next section of chapters addresses how the wind resource data are analyzed.
It starts with quality control (QC) and validation and then moves on to characteriz-
ing the observed wind resource. Subsequent chapters cover extrapolating the resource
estimates to hub height, correcting short-term measurements to long-term historical
conditions, and wind flow modeling. Chapter 14 is devoted to special issues con-
cerning offshore sites. Chapter 15 discusses uncertainty in wind resource estimates,
including the different categories of uncertainty and their typical values. The last
chapter, Chapter 16, provides an overview of the steps involved in designing a wind
project and estimating its long-term average energy production.
In most chapters, discussion questions aimed at classroom use and recommenda-
tions for further reading are provided.
1.5 QUESTIONS FOR DISCUSSION
1. What is the principal cause of pressure gradients (differences) between different
points on the earth's surface? When a pressure gradient increases, how does the
wind tend to change?
2. What are the three principal mechanisms affecting the speed and direction of
the wind near the earth's surface?
3. Give two examples of mesoscale atmospheric circulations. Does either of these
mechanisms occur in the country or region where you live? If so, where?
4. What would have a larger surface roughness length, a grass field or a forest?
All other things being equal, how is this difference likely to affect wind speeds
at the height of a wind turbine?
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