Solar Engineering of Thermal Processes, 4th Edition

Chapter 24

Wind Energy

Wind energy is an indirect form of solar energy; the solar heating of the atmosphere along with the earth's rotation creates planetary and local wind patterns. In this chapter the wind resource is described and a method for reducing wind data to a useful mathematical form is presented. A simplified theory of wind turbines is then presented. This simplified theory leads to a basic understanding of the characteristics of actual wind turbines. Combining the analytical description of the wind resource with the characteristic of an actual wind turbine leads to a prediction of electrical energy production. Much about wind energy is not discussed in this chapter, such as the complex meteorology that produces favorable wind sites, the aerodynamics of turbine blades, the needed controls for producing acceptable electrical waveforms, the mechanical aspects of gears trains and tower structures, the visual and avian siting issues, and noise problems.

24.1 Introduction

Windmills (wind machines used to mill grain) have been used for more than two thousand years. One of the earliest descriptions is of Persian windmills found in Arab writings of the ninth century describing windmills in use in the seventh century (El-Wakil, 1984). However, it is believed that the Persians had vertical-axis grindstones as early as about 200 bc (Eldridge, 1980).

A large variety of wind turbines have been suggested and used at various times and for various purposes. Figures 24.1.1(a) and (b) ...