INNOVATION IN WIND TURBINE DESIGN

Content: Foreword xvPreface xviiAcknowledgement xixIntroduction 10.1 Why Innovation? 10.2 The Challenge of Wind 20.3 The Specification of a Modern Wind Turbine 20.4 The Variability of the Wind 40.5 Early Electricity-Generating Wind Turbines 40.6 Commercial Wind Technology 60.7 Basis of Wind Technology Evaluation 70.7.1 Standard Design as Baseline 70.7.2 Basis of Technological Advantage 70.7.3 Security of Claimed Power Performance 80.7.4 Impact of Proposed Innovation 80.8 Competitive Status of Wind Technology 8References 9Part I Design Background 11 1 Rotor Aerodynamic Theory 131.1 Introduction 131.2 Aerodynamic Lift 141.3 Power in the Wind 161.4 The Actuator Disc Concept 171.5 Open Flow Actuator Disc 191.5.1 Power Balance 191.5.2 Axial Force Balance 201.5.3 Froude's Theorem and the Betz Limit 201.5.4 The Power Extraction Process 221.5.5 Relativity in a Fluid Flow Field 231.6 Why a Rotor? 251.7 Actuator Disc in Augmented Flow and Ducted Rotor Systems 261.7.1 Fundamentals 261.7.2 Generalised Actuator Disc 281.7.3 The Force on a Diffuser 361.7.4 Generalised Actuator Disc Theory and Realistic Diffuser Design 371.8 Blade Element Momentum Theory 381.8.1 Introduction 381.8.2 Momentum Equations 381.8.3 Blade Element Equations 401.8.4 Non-dimensional Lift Distribution 401.8.5 General Momentum Theory 411.8.6 BEM in Augmented Flow 421.8.7 Closed-Form BEM Solutions 441.9 Optimum Rotor Design 461.9.1 Optimisation to Maximise Cp 461.9.2 The Power Coefficient, Cp 481.9.3 Thrust Coefficient 511.9.4 Out-of-Plane Bending Moment Coefficient 521.9.5 Optimisation to a Loading Constraint 541.9.6 Optimisation of Rotor Design and Hub Flow 561.10 Limitations of Actuator Disc and BEM Theory 571.10.1 Actuator Disc Limitations 571.10.2 Inviscid Modelling and Real Flows 581.10.3 Wake Rotation and Tip Effect 581.10.4 Optimum Rotor Theory 591.10.5 Skewed Flow 591.10.6 Summary of BEM Limitations 59References 602 Rotor Aerodynamic Design 652.1 Optimum Rotors and Solidity 652.2 Rotor Solidity and Ideal Variable Speed Operation 662.3 Solidity and Loads 682.4 Aerofoil Design Development 682.5 Sensitivity of Aerodynamic Performance to Planform Shape 732.6 Aerofoil Design Specification 742.7 Aerofoil Design for Large Rotors 75References 773 Rotor Structural Interactions 793.1 Blade Design in General 793.2 Basics of Blade Structure 803.3 Simplified Cap Spar Analyses 823.3.1 Design for Minimum Mass with Prescribed Deflection 833.3.2 Design for Fatigue Strength: No Deflection Limits 833.4 The Effective t/c Ratio of Aerofoil Sections 843.5 Blade Design Studies: Example of a Parametric Analysis 853.6 Industrial Blade Technology 913.6.1 Design 913.6.2 Manufacturing 923.6.3 Design Development 94References 944 Upscaling of Wind Turbine Systems 974.1 Introduction: Size and Size Limits 974.2 The 'Square-Cube' Law 1004.3 Scaling Fundamentals 1004.4 Similarity Rules for Wind Turbine Systems 1024.4.1 Tip Speed 1024.4.2 Aerodynamic Moment Scaling 1034.4.3 Bending Section Modulus Scaling 1034.4.4 Tension Section Scaling 1034.4.5 Aeroelastic Stability 1034.4.6 Self-Weight Load Scaling 1034.4.7 Blade (Tip) Deflection Scaling 1044.4.8 More Subtle Scaling Effects and Implications 1044.4.8.1 Size Effect 1044.4.8.2 Aerofoil Boundary Layer 1044.4.8.3 Earth's Boundary Layer, Wind Shear and Turbulence 1044.4.9 Gearbox Scaling 1054.4.10 Support Structure Scaling 1054.4.11 Power/Energy Scaling 1054.4.12 Electrical Systems Scaling 1064.4.13 Control Systems Scaling 1064.4.14 Scaling Summary 1064.5 Analysis of Commercial Data 1074.5.1 Blade Mass Scaling 1084.5.2 Shaft Mass Scaling 1114.5.3 Scaling of Nacelle Mass and Tower Top Mass 1124.5.4 Tower Top Mass 1144.5.5 Tower Scaling 1144.5.5.1 Height versus Diameter 1144.5.5.2 Mass versus Diameter 1154.5.5.3 Normalised Mass versus Diameter 1164.5.6 Gearbox Scaling 1184.6 Upscaling of VAWTs 1194.7 Rated Tip Speed 1204.8 Upscaling of Loads 1214.9 Violating Similarity 1234.10 Cost Models 1244.11 Scaling Conclusions 125References 1265 Wind Energy Conversion Concepts 127References 1296 Drive-Train Design 1316.1 Introduction 1316.2 Definitions 1316.3 Objectives of Drive-Train Innovation 1326.4 Drive-Train Technology Maps 1326.5 Direct Drive 1366.6 Hybrid Systems 1396.7 Geared Systems - the Planetary Gearbox 1406.8 Drive Trains with Differential Drive 1446.9 Hydraulic Transmission 1456.10 Efficiency of Drive-Train Components 1486.10.1 Introduction 1486.10.2 Efficiency over the Operational Range 1506.10.3 Gearbox Efficiency 1516.10.4 Generator Efficiency 1526.10.5 Converter Efficiency 1536.10.6 Transformer Efficiency 1536.10.7 Fluid Coupling Efficiency 1536.11 Drive-Train Dynamics 1546.12 The Optimum Drive Train 1556.13 Innovative Concepts for Power Take-Off 157References 1607 Offshore Wind Technology 1637.1 Design for Offshore 1637.2 High-Speed Rotor 1647.2.1 Design Logic 1647.2.2 Speed Limit 1647.2.3 Rotor Configurations 1657.2.4 Design Comparisons 1677.3 'Simpler' Offshore Turbines 1707.4 Rating of Offshore Wind Turbines 1717.5 Foundation and Support Structure Design 1727.5.1 Foundation Design Concepts 1727.5.2 Support Structure Design Concepts 1737.5.3 Loads, Foundations and Costs 1747.6 Electrical Systems of Offshore Wind Farms 1757.6.1 Collection System for an Offshore Wind Farm 1757.6.2 Integration of Offshore Wind Farms into Electrical Networks 1777.6.2.1 High-Voltage Alternating Current (HVAC) 1777.6.2.2 Current-Source Converter (CSC) 1797.6.2.3 Voltage-Source Converter for Offshore Wind Farm Integration 1807.7 Operations and Maintenance (O&M) 1807.7.1 Introduction 1807.7.2 Modelling 1817.7.3 Inspection of Wind Turbines 1827.8 Offshore Floating Wind Turbines 183References 1888 Future Wind Technology 1918.1 Evolution 1918.2 Present Trends - Consensus in Blade Number and Operational Concept 1938.3 Present Trends - Divergence in Drive-Train Concepts 1948.4 Future Wind Technology - Airborne 1948.4.1 Introduction 1948.4.2 KPS - Cable Tension Power Take-Off 1988.4.2.1 Earth Axes 1988.4.2.2 Kite Axes 1988.4.2.3 BEM Application to the Kite as an Aerofoil Section (No Tip Loss Applied) 1998.4.3 Daisy Kite - Rotary Power Transmission 2028.4.4 Omnidea - Rotating Cylindrical Balloon as a Lifting Body 2038.4.5 Makani 2038.4.6 Airborne Conclusions 2048.5 Future Wind Technology - Energy Storage 2048.5.1 Types of Energy Storage 2048.5.2 Battery Storage 2048.5.3 Gas Pressure Storage 2058.5.4 Compressed Air Storage 2058.5.5 Flywheel Energy Storage 2068.5.6 Thermal Energy Storage 2068.6 Innovative Energy Conversion Solutions 2078.6.1 Electrostatic Generator 2078.6.2 Vibrating Column 208References 208Part II Technology Evaluation 2119 Cost of Energy 2139.1 The Approach to Cost of Energy 2139.2 Energy: the Power Curve 2169.3 Energy: Efficiency, Reliability, Availability 2229.3.1 Efficiency 2229.3.2 Reliability 2229.3.3 Availability 2239.4 Capital Costs 2249.5 Operation and Maintenance 2259.6 Overall Cost Split 2269.7 Scaling Impact on Cost 2279.8 Impact of Loads (Site Class) 228References 23210 Evaluation Methodology 23510.1 Key Evaluation Issues 23510.2 Fatal Flaw Analysis 23510.3 Power Performance 23610.3.1 The Betz Limit 23610.3.2 The Pressure Difference across a Wind Turbine 23710.3.3 Total Energy in the Flow 23810.4 Structure and Essential Mass 23910.5 Drive-Train Torque 24110.6 Representative Baseline 24110.7 Design Loads Comparison 24210.8 Evaluation Example: Optimum Rated Power of a Wind Turbine 24410.9 Evaluation Example: the Carter Wind Turbine and Structural Flexibility 24610.10 Evaluation Example: Concept Design Optimisation Study 24910.11 Evaluation Example: Ducted Turbine Design Overview 25110.11.1 Extreme Loads 25110.11.2 Drive-Train Torque 25210.11.3 Energy Capture 252References 253Part III Design Themes 25511 Optimum Blade Number 25711.1 Energy Capture Comparisons 25711.2 Blade Design Issues 25811.3 Operational and System Design Issues 26011.4 Multi-bladed Rotors 265References 26612 Pitch versus Stall 26712.1 Stall Regulation 26712.2 Pitch Regulation 26912.3 Fatigue Loading Issues 27012.4 Power Quality and Network Demands 27212.4.1 Grid Code Requirements and Implications for Wind Turbine Design 272References 27413 HAWT or VAWT? 27713.1 Introduction 27713.2 VAWT Aerodynamics 27713.3 Power Performance and Energy Capture 28213.4 Drive-Train Torque 28413.5 Niche Applications for VAWTs 28613.6 Status of VAWT Design 28613.6.1 Problems 28613.6.2 Advances in VAWT Understanding and Technology 287References 28914 Free Yaw 29114.1 Yaw System COE Value 29114.2 Yaw Dynamics 29114.3 Yaw Damping 29314.4 Main Power Transmission 29314.5 Operational Experience of Free Yaw Wind Turbines 29414.6 Summary View 295References 29515 Multi-rotor Systems (MRS) 29715.1 Introduction 29715.2 Standardisation Benefit and Concept Developments 29715.3 Operational Systems 29815.4 Scaling Economics 29815.5 History Overview 30015.6 Aerodynamic Performance of Multi-rotor Arrays 30015.7 Recent Multi-rotor Concepts 30115.8 MRS Design Based on VAWT Units 30415.9 MRS Design within the Innwind.EU Project 30615.9.1 Loads, Structure and Yaw System Design 30615.9.2 Operations and Maintenance 30815.9.3 Cost of Energy Evaluation 30915.10 Multi-rotor Conclusions 311References 31116 Design Themes Summary 313Part IV Innovative Technology Examples 31517 Adaptable Rotor Concepts 31717.1 Rotor Operational Demands 31717.2 Management of Wind Turbine Loads 31917.3 Control of Wind Turbines 32017.4 LiDAR 32117.4.1 Introduction 32117.4.2 The LiDAR Operational Principle 32117.4.3 Evaluation of LiDAR for Control of Wind Turbines 32217.4.4 An Example of Future Innovation in LiDAR 32317.5 Adaptable Rotors 32317.6 The Coning Rotor 32617.6.1 Concept 32617.6.2 Coning Rotor: Outline Evaluation - Energy Capture 32817.6.3 Coning Rotor: Outline Evaluation - Loads 32917.6.4 Concept Overview 33017.7 Variable Diameter Rotor 330References 33218 Ducted Rotors 33518.1 Introduction 33518.2 The Katru Shrouded Rotor System 33618.3 The Wind Lens Ducted Rotor 340References 34419 The Gamesa G10X Drive Train 34520 DeepWind Innovative VAWT 34920.1 The Concept 34920.1.1 Blades 34920.1.2 Controls 35120.1.3 Generator Concepts 35120.1.4 Torque Absorption 35320.1.5 Anchoring Part 35320.2 DeepWind Concept at 5 MW Scale 35320.3 Marine Operations Installation, Transportation and O&M 35320.4 Testing and Demonstration 35320.5 Cost Estimations 355References 35621 Gyroscopic Torque Transmission 357References 36222 The Norsetek Rotor Design 363References 36523 Siemens Blade Technology 36724 Stall-Induced Vibrations 371References 37425 Magnetic Gearing and Pseudo-Direct Drive 37725.1 Magnetic Gearing Technology 37725.2 Pseudo-Direct-Drive Technology 380References 38226 Summary and Concluding Comments 383Index 385