Wind Energy Conversion

Abstract

Wind is the air-in-motion. On Earth, it has two major components: (i) Planetary winds resulting from daily rotation of the earth and differential solar heating of earth and its atmosphere between polar and equatorial regions (ii) Local winds resulting from unequal heating and cooling of ground surface and ocean/lake surface during day and night. Wind Energy is a manifestation of the solar Energy. The wind has been playing a significant role in human development and civilization. The first ever known utility of wind energy is sea transport in Egypt way back 5000 years where boats were used to sail from shore to shore. The first windmill was built as early as 2000 B.C. in ancient Babylon, which is a system with vanes attached to its axis to produce circular motion (Gipe P. Wind energy comes of age. Wiley, New York, 1995). The grain grinding and water pumping were main applications of windmill. Although a large number of concepts of wind electrical generator (aero generators) have been introduced from time to time, there are basically two designs which have been put to real applications. These wind energy conversion systems may be classified mainly based on the direction of their axis of rotation. Two broad categories are wind axis (or horizontal axis) and cross wind (or vertical axis) machines. Horizontal Axis Wind Machines (Propeller Type) are wind turbines whose axis of rotation is parallel to the air stream. Some types of horizontal wind turbine with variable degree of operational and efficiency characteristics are shown in Fig. 10.1. Large Horizontal Axis Wind Turbines have a yaw adjustment mechanism that automatically positions the wind turbine head to face against the direction of the wind. This enables these turbines to maximize energy conversion efficiency. The configuration of a typical horizontal axis wind turbine with various components is shown in Fig. 10.2. Lift machines can have blade sections moving considerably faster than the wind speed, e.g. a keeled sail boat which can sail faster than wind. Vertical-Axis Wind Turbines accept wind from any direction without adjustment. Gearing and generators can be directly coupled to the axis at ground level. Various vertical wind energy conversion systems are shown in Fig. 10.3.