Introduction

A successful blade design must satisfy a wide range of objectives, some of which are in conflict. These objectives can be summarized as follows:

(1) maximize annual energy yield for the specified wind speed distribution;

(2) limit maximum power output (in the case of stall regulated machines);

(3) resist extreme and fatigue loads;

(4) restrict tip deflections to avoid blade/tower collisions (in the case of upwind machines);

(5) avoid resonances;

(6) minimize weight and cost.

The design process can be divided into two stages: the aerodynamic design, in which objectives (1) and (2) are satisfied, and the structural design. The aerodynamic design addresses the selection of the optimum geometry of the blade external surface - normally simply referred to as the blade geometry - which is defined by the aerofoil family and the chord, twist and thickness distributions. The structural design consists of blade material selection and the determination of a structural cross section or spar within the external envelope that meets objectives (4) to (6). Inevitably there is interaction between the two stages, as the blade thickness needs to be large enough to accommodate a spar which is structurally efficient.

The focus of Section 7.1 is on blade structural design. After a brief consideration of the aerodynamic design in Section 7.1.2, practical constraints on the optimum design are noted in Section 7.1.3 and forms of blade structure surveyed in Section 7.1.4. An overview of the properties of some potential blade materials is given in Section 7.1.5 and the properties of glass-fibre reinforced plastic (GFRP) and laminated wood are considered in more detail in Sections 7.1.6 and 7.1.7. Governing load cases are considered in Sections 7.1.8 with reference to both stall- and pitch-

regulated machines. Subsequent sections touch upon blade resonance, panel buckling design and blade root fixings.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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