Onshore and Offshore Wind Energy: An Introduction

Acknowledgements xi

1. Introduction 1

1.1 Wind energy and Planet Earth 1

1.2 Winds of the world 5

1.3 From windmills to wind turbines 9

1.4 Power, energy and performance 17

1.5 Coming up to date 24

References 29

2. Capturing the wind 31

2.1 Wind speed and power 31

2.2 Wild wind 37

2.2.1 Introductory 37

2.2.2 Wind statistics 40

2.2.3 Mapping and forecasting 49

2.3 Predicting turbine output 57

References 61

3. Wind turbines 63

3.1 Turbine types and sizes 63

3.2 Aerodynamics 69

3.2.1 Rotor effi ciency and the Betz Limit 69

3.2.2 Lift and drag 72

3.2.3 Rotor speed 80

3.2.4 Rotor blades 87

3.2.4.1 Choosing airfoils 87

3.2.4.2 Stall and pitch control 90

3.3 Mechanics 94

3.3.1 Gearboxes 94

3.3.2 Towers 97

3.3.3 Vibration and fatigue 98

3.4 Electrics 107

3.4.1 AC electricity 107

3.4.2 Generators 116

3.4.2.1 Introductory 116

3.4.2.2 Synchronous generators 122

3.4.2.3 Asynchronous generators 128

3.4.2.3.1 Squirrel-cage and wound-rotor induction machines 128

3.4.2.3.2 Doubly-fed induction generators 133

3.5 Turbine control 138

3.6 Onshore wind farms 143

3.6.1 Introductory 143

3.6.2 Siting and spacing 146

3.6.3 Monitoring and control 150

References 152

4. Moving offshore 153

4.1 Introductory 153

4.2 Wind and waves 157

4.3 Turbines and foundations 161

4.4 Offshore wind farms 166

4.4.1 Case study: Horns Rev 2 166

4.4.2 Case study: London Array 170

4.5 Bringing the power ashore 173

References 177

5. Grid integration 179

5.1 Setting the scene 179

5.2 Connecting to the grid 182

5.2.1 Grid strength and fault levels 182

5.2.2 Electrical quality 186

5.3 Large-scale wind power 190

5.3.1 Introductory 190

5.3.2 Intermittency and variability 191

5.3.3 Capacity credit and backup generation 194

References 198

6. Economics and the environment 199

6.1 Wind energy economics 199

6.1.1 Capital and installation costs 199

6.1.2 Operation, maintenance and cash fl ow 202

6.2 Environmental aspects 204

6.2.1 Introductory 204

6.2.2 Landscape and amenity 207

6.2.3 Birds, bats and farming 211

6.2.4 Seabirds, fi sh and marine conservation 216

References 218

Index 219