Characteristics of the Wind - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 526

Wind Turbine Siting
The major goal in siting wind turbines is to maximize energy capture and thereby
reduce the unit cost of generating electricity. Maximum energy capture can be difficult to
achieve because of the wide variability of the wind over both space and time. The first step
in site analysis is to examine all available information, such as the Wind Energy Resource
Atlas of the United States [Elliott et al. 1986]. Although wind resource maps identify many
promising areas, they do not depict variability caused by local terrain features. Siting of
a wind turbine relative to local factors, which is termed micrositing , is described in this
section. The scale of the turbines to be sited can determine the specific procedures used.
Siting Small-Scale Wind Turbines
Small-scale wind turbines (rotor diameters up to about 12 m) are typically used to gen-
erate power for consumption near the turbine by a private household or a small business.
This restricts the location of the machine to a relatively small area. The siting approach
under these circumstances must address two basic problems: finding the best (or at least
the most acceptable) site for the turbine in a given area, and accurately estimating the wind
characteristics at the selected site. Picking the initial location can be done using empiri-
cal guidelines formulated for evaluating the effects of the local topography and roughness
elements on the wind, including the effects of trees and buildings [ e.g. Frost and Nowak
1979, Wegley et al. 1980, Frost and Shieh 1981].
Depending on the time and funds available, there are three possible approaches for
estimating the wind characteristics at the site: first, using wind data from a nearby site,
which is the quickest and least costly approach; second, correlating limited on-site wind
measurements with data from a nearby site; and third, collecting a representative data
sample at the proposed site, which is the most accurate approach, but also the most time
consuming and most expensive. The success of the first and second approaches depends
very heavily on the complexity of the terrain between the proposed site and site where data
were collected and on whether the two locations are similarly exposed to the prevailing
wind in the area.
Siting Medium- and Large-Scale Wind Turbines for Utility Applications
The meteorological aspects of siting medium- and large-scale wind turbines have been
documented by Hiester and Pennell [1981]. These methods also apply to wind power
stations composed of large numbers of medium-scale machines. Siting activities for util-
ity applications include more than just the identification of a large, windy site. Economic
viability, compatibility with wind turbine design capabilities, and accept-ability to the public
are also important. Formal stepwise procedures have been established to help wind power
developers through the decision process involved in locating large, viable wind turbine sites
[Pennell 1982]. This process combines the meteorological aspects of siting ( e.g. , annual
average wind speed, frequency distribution, persistence, turbulence, and wind shear) with
the non-meteorological aspects (economic potential, safety, and environmental consider-
ations) that are equally essential to a successful wind power project. Only the meteorologi-
cal aspects of siting will be discussed here.
The spacing between turbines in a wind power station is an important factor in
extracting maximum energy from the wind without significantly affecting turbine life.
Optimal spacing requires knowledge of the size and intensity of wakes downwind of each
type of turbine. The wake analysis problem is complicated by the terrain-induced
variability of the ambient wind over the station. The nature of this variability and