Innovation in Wind Turbine Design

Peter Jamieson, Principal Engineer, Special Projects Department, Garrad Hassan & Partners Ltd., Edinburgh, Scotland Peter Jamieson has been in the wind industry since 1980, and with Garrad Hassan since 1991 as a founding founder member of their Scottish office. He was previously with James Howden of Glasgow who manufactured wind turbines from 1980 1988. He currently heads the "Special Projects" department in Garrad Hassan with involvement in innovative designs of wind turbine and component developments. He is also involved in technology review for government, wind industry and commercial organisations. He has authored circa 30 published papers on wind energy topics, as well as magazine articles, and authored much of the technological content for the EWEA (European Wind Energy Association) publication Wind Energy: The Facts. He holds a number of patents on wind turbine rotor technology.

Acknowledgements xiii
Foreword xv
Preface xvii
Introduction 1
0.1 Why Innovation? 1
0.2 The Challenge of Wind 2
0.3 The Specification of a Modern Wind Turbine 2
0.4 The Variability of the Wind 4
0.5 Commercial Wind Technology 4
0.6 Basis of Wind Technology Evaluation 5
0.6.1 Standard Design as Baseline 5
0.6.2 Basis of Technological Advantage 6
0.6.3 Security of Claimed Power Performance 6
0.6.4 Impact of Proposed Innovation 6
References 7
Part I DESIGN BACKGROUND
1 Rotor Aerodynamic Theory 11
1.1 Introduction 11
1.2 Aerodynamic Lift 12
1.3 The Actuator Disc 14
1.4 Open Flow Actuator Disc 15
1.4.1 Axial Induction 15
1.4.2 Momentum 16
1.5 Generalised Actuator Disc Theory 17
1.6 The Force on a Diffuser 23
1.7 Generalised Actuator Disc Theory and Realistic Diffuser Design 24
1.8 Why a Rotor? 24
1.9 Basic Operation of a Rotor 25
1.10 Blade Element Momentum Theory 27
1.10.1 Momentum Equations 27
1.10.2 Blade Element Equations 28
1.11 Optimum Rotor Theory 30
1.11.1 The Power Coefficient, Cp 33
1.11.2 Thrust Coefficient 36
1.11.3 Out–of–Plane Bending Moment Coefficient 36
1.12 Generalised BEM 38
1.13 Limitations of Actuator Disc and BEM Theory 41
1.13.1 Actuator Disc Limitations 41
1.13.2 Wake Rotation and Tip Effect 41
1.13.3 Optimum Rotor Theory 42
1.13.4 Skewed Flow 42
1.13.5 Summary 42
References 43
2 Rotor Aerodynamic Design 45
2.1 Optimum Rotors and Solidity 45
2.2 Rotor Solidity and Ideal Variable Speed Operation 46
2.3 Solidity and Loads 48
2.4 Aerofoil Design Development 48
2.5 Sensitivity of Aerodynamic Performance to Planform Shape 52
2.6 Aerofoil Design Specification 54
References 55
3 Rotor Structural Interactions 57
3.1 Blade Design in General 57
3.2 Basics of Blade Structure 58
3.3 Simplified Cap Spar Analyses 60
3.3.1 Design for Minimum Mass with Prescribed Deflection 61
3.3.2 Design for Fatigue Strength: No Deflection Limits 61
3.4 The Effective t/c Ratio of Aerofoil Sections 62
3.5 Blade Design Studies: Example of a Parametric Analysis 64
3.6 Industrial Blade Technology 69
3.6.1 Design 69
3.6.2 Manufacturing 69
3.6.3 Design Development 70
References 73
4 Upscaling of Wind Turbine Systems 75
4.1 Introduction: Size and Size Limits 75
4.2 The Square–Cube Law 78
4.3 Scaling Fundamentals 78
4.4 Similarity Rules for Wind Turbine Systems 80
4.4.1 Tip Speed 80
4.4.2 Aerodynamic Moment Scaling 81
4.4.3 Bending Section Modulus Scaling 81
4.4.4 Tension Section Scaling 81
4.4.5 Aeroelastic Stability 81
4.4.6 Self Weight Loads Scaling 81
4.4.7 Blade (Tip) Deflection Scaling 82
4.4.8 More Subtle Scaling Effects and Implications 82
4.4.9 Gearbox Scaling 83
4.4.10 Support Structure Scaling 83
4.4.11 Power/Energy Scaling 83
4.4.12 Electrical Systems Scaling 84
4.4.13 Control Systems Scaling 84
4.4.14 Scaling Summary 84
4.5 Analysis of Commercial Data 85
4.5.1 Blade Mass Scaling 86
4.5.2 Shaft Mass Scaling 90
4.5.3 Scaling of Nacelle Mass and Tower Top Mass 90
4.5.4 Tower Top Mass 91
4.5.5 Tower Scaling 92
4.5.6 Gearbox Scaling 96
4.6 Upscaling of VAWTs 97
4.7 Rated Tip Speed 97
4.8 Upscaling of Loads 99
4.9 Violating Similarity 101
4.10 Cost Models 101
4.11 Scaling Conclusions 103
References 103
5 Wind Energy Conversion Concepts 105
References 107
6 Drive Train Design 109
6.1 Introduction 109
6.2 Definitions 109
6.3 Objectives of Drive Train Innovation 110
6.4 Drive Train Technology Maps 110
6.5 Direct Drive 114
6.6 Hybrid Systems 117
6.7 Hydraulic Transmission 118
6.8 Efficiency of Drive Train Components 120
6.8.1 Introduction 120
6.8.2 Efficiency Over the Operational Range 121
6.8.3 Gearbox Efficiency 122
6.8.4 Generator Efficiency 122
6.8.5 Converter Efficiency 123
6.8.6 Transformer Efficiency 124
6.8.7 Fluid Coupling Efficiency 124
6.9 The Optimum Drive Train 125
6.10 Innovative Concepts for Power Take–Off 126
References 129
7 Offshore Wind Turbines 131
7.1 Design for Offshore 131
7.2 High Speed Rotor 132
7.2.1 Design Logic 132
7.2.2 Speed Limit 132
7.2.3 Rotor Configurations 133
7.2.4 Design Comparisons 134
7.3 Simpler Offshore Turbines 138
7.4 Offshore Floating Turbine Systems 139
References 141
8 Technology Trends Summary 143
8.1 Evolution 143
8.2 Consensus in Blade Number and Operational Concept 145
8.3 Divergence in Drive Train Concepts 145
8.4 Future Wind Technology 146
8.4.1 Introduction 146
8.4.2 Airborne Systems 146
8.4.3 New System Concepts 147
References 149
Part II TECHNOLOGY EVALUATION
9 Cost of Energy 153
9.1 The Approach to Cost of Energy 153
9.2 Energy: The Power Curve 156
9.3 Energy: Efficiency, Reliability, Availability 161
9.3.1 Efficiency 161
9.3.2 Reliability 161
9.3.3 Availability 162
9.4 Capital Costs 163
9.5 Operation and Maintenance 164
9.6 Overall Cost Split 164
9.7 Scaling Impact on Cost 166
9.8 Impact of Loads (Site Class) 167
References 170
10 Evaluation Methodology 173
10.1 Key Evaluation Issues 173
10.2 Fatal Flaw Analysis 174
10.3 Power Performance 174
10.3.1 The Betz Limit 175
10.3.2 The Pressure Difference across a Wind Turbine 176
10.3.3 Total Energy in the Flow 177
10.4 Drive Train Torque 178
10.5 Representative Baseline 178
10.6 Design Loads Comparison 179
10.7 Evaluation Example: Optimum Rated Power of a Wind Turbine 181
10.8 Evaluation Example: The Carter Wind Turbine and Structural Flexibility 183
10.9 Evaluation Example: Concept Design Optimisation Study 186
References 187
Part III DESIGN THEMES
11 Optimum Blade Number 191
11.1 Energy Capture Comparisons 191
11.2 Blade Design Issues 192
11.3 Operational and System Design Issues 194
11.4 Multi Bladed Rotors 199
References 199
12 Pitch versus Stall 201
12.1 Stall Regulation 201
12.2 Pitch Regulation 203
12.3 Fatigue Loading Issues 204
12.4 Power Quality and Network Demands 206
12.4.1 Grid Code Requirements and Implications
for Wind Turbine Design 206
References 208
13 HAWT or VAWT? 211
13.1 Introduction 211
13.2 VAWT Aerodynamics 211
13.3 Power Performance and Energy Capture 217
13.4 Drive Train Torque 218
13.5 Niche Applications for VAWTs 220
13.6 Status of VAWT Design 220
13.6.1 Problems 220
13.6.2 Solutions? 221
References 222
14 Free Yaw 223
14.1 Yaw System COE Value 223
14.2 Yaw Dynamics 223
14.3 Yaw Damping 225
14.4 Main Power Transmission 225
14.5 Operational Experience of Free Yaw Wind Turbines 226
14.6 Summary View 227
References 227
15 Multi Rotor Systems 229
15.1 Introduction 229
15.2 Standardisation Benefit and Concept Developments 229
15.3 Operational Systems 230
15.4 Scaling Economics 230
15.5 History Overview 232
15.6 Aerodynamic Performance of Multi Rotor Arrays 232
15.7 Recent Multi Rotor Concepts 232
15.8 Multi Rotor Conclusions 237
References 238
16 Design Themes Summary 239
Part IV INNOVATIVE TECHNOLOGY EXAMPLES
17 Adaptable Rotor Concepts 243
17.1 Rotor Operational Demands 243
17.2 Control of Wind Turbines 245
17.3 Adaptable Rotors 246
17.4 The Coning Rotor 248
17.4.1 Concept 248
17.4.2 Coning Rotor: Outline Evaluation Energy Capture 250
17.4.3 Coning Rotor: Outline Evaluation Loads 250
17.4.4 Concept Overview 251
17.5 Variable Diameter Rotor 252
References 253
18 A Shrouded Rotor 255
References 258
19 The Gamesa G10X Drive Train 259
20 Gyroscopic Torque Transmission 263
References 268
21 The Norsetek Rotor Design 269
References 271
22 Siemens Blade Technology 273
23 Stall Induced Vibrations 277
References 280
24 Magnetic Gearing and Pseudo–Direct Drive 283
24.1 Magnetic Gearing Technology 283
24.2 Pseudo–Direct Drive Technology 286
References 288
25 Summary and Concluding Comments 289
Index 291