**1. Introduction**

Numerous research contributions in developing wind industry technologies worldwide have been initiated since the oil crisis in 1973, and various configurations of wind turbines and large-scale wind farms have been installed in many places. These clean energy sources can make a substantial and economically competitive contribution to the future energy needs.

Irrespective of the specific application, a wind turbine system design should be based on the cost-effective production of energy. The main objective should be based on the minimum cost of energy depending on the rotor diameter, rated power as well as the wind characteristics for a given site. The economic feasibility of large-scale wind turbines operated as a part of electrical power systems has been considered by H. M. Bae [1]. In this paper, the design variables were taken to be the rotor diameter, rated power, and number of the installed machines. Maximization of the total net value of the generated power, which is equal to the annual expected fuel cost savings minus the total cost of the system, was taken as the main system objective. Power was considered as constraint rather than design objective. Hansen [2] addressed optimum blade shapes for maximizing the power coefficient of the rotor. He presented a method to obtain the optimum blade chord and twist distributions for better aerodynamic performance. Another important consideration in the design of wind energy generator systems is to reduce vibration without increasing structural weight. This is because the economics require that large wind turbines operate reliably for long periods of time while subject to significant vibratory loads [3, 4].

In this chapter, the wind turbine will be analyzed as a system in order to build a general model for its structural design optimization. The most significant design objectives as well as design environment and constraints are defined and measured. All effective system design variables and parameters are identified and discussed. Several design alternatives will be considered to see how the various design criteria are affected in each case.

### **2. System definition and main function**

A wind turbine can be defined as a device that converts the wind's kinetic energy into useful mechanical power. This produced power can be exploited in many applications such as:


The present chapter focuses on horizontal-axis wind turbines (HAWTs) utilized for electricity generation.
