Innovation in Wind Turbine Design

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