Foreword ..................................................... xvii
Preface ....................................................... xix
1 Chronological History of Wind Turbine Technology ............. 1
1.1 Introduction ............................................ 1
1.2 Major Benefits and Problems Associated with Alternate
Energy Sources .......................................... 3
1.3.1 Benefits ......................................... 4
1.3.2 Disadvantages .................................... 5
1.3.3 Unique Installation Requirements ................. 6
1.3.4 Repowering to Increase Output by Existing
Turbines ......................................... 6
1.4 Worldwide Utilization of Wind Turbines .................. 7
1.4.1 Denmark .......................................... 7
1.4.2 Germany .......................................... 8
1.4.3 China ............................................ 8
1.4.4 United States .................................... 9
1.4.5 Canada ........................................... 9
1.4.6 Belgium and the Netherlands ..................... 10
1.4.7 United Kingdom .................................. 10
1.4.8 France .......................................... 10
1.4.9 Russia .......................................... 11
1.4.10 Italy ........................................... 11
1.4.11 Early Wind Turbine Development: Summary ......... 11
1.5 Operating Principles of Wind Turbines .................. 13
1.5.1 Critical Elements of Wind Turbine Systems and
Their Principal Functions ....................... 14
1.6 Wind Turbine Classifications ........................... 16
1.6.1 Utility-Scale Wind Turbine Sources .............. 16
1.6.2 Pay-Off Periods for Utility-Scale Wind
Turbines and Wind Farms ......................... 17
1.6.3 Small-Scale Wind Turbines ....................... 18
1.6.4 Component Cost Estimates for Small Wind
Turbine Systems ................................. 19
1.6.5 Total Installed Cost for 5-kW Wind Turbine in
2009 ............................................ 19
1.6.6 Wind Turbine and Tower Installers ............... 20
1.6.7 Potential Applications of Small Wind Turbines ... 21
1.6.8 Intermediate-Scale Wind Turbines ................ 21
1.7 Wind Farm Developers ................................... 21
1.7.1 Wind Farm Dealers ............................... 22
1.7.2 Renewable Energy Professionals .................. 22
1.8 Design Configurations .................................. 22
1.8.1 Residential Design Configurations with Off-
Grid Capabilities ............................... 23
1.8.2 Residential Design Configurations with Grid-
Tied and Back-Up Capabilities ................... 23
1.8.3 Residential Design Configurations with Grid-
Tied and No-Battery Operation ................... 23
1.8.4 Hybrid Solar-Wind Turbine System
Configurations .................................. 24
1.8.5 Compact Wind Turbine and Energy Systems for
Dual Applications ............................... 25
1.8.6 Critical Electrical Components .................. 25
1.9 Next Generation Wind Turbines with Unique Features ..... 26
1.9.1 Helix Wind Turbines ............................. 26
1.9.2 Wind Turbines Operating from Ocean Surfaces ..... 26
1.9.3 Wind Turbine Design Based on Jet Engine ......... 26
1.9.4 Vertical Axis Wind Turbines ..................... 27
1.9.5 Floating Offshore Wind Turbines ................. 27
1.10 Typical Wind Power Estimates for United States ......... 28
1.11 Summary ................................................ 28
References ............................................. 29
2 Design Aspects and Performance Requirements ................. 31
2.1 Introduction ........................................... 31
2.2 Types of Wind Turbines ................................. 32
2.2.1 Windmills ....................................... 34
2.2.2 Farm Type and Dutch Type Wind Turbines .......... 35
2.3 Modern Wind Turbines ................................... 35
2.3.1 Horizontal Axis Wind Turbine (HAWT) ............. 36
2.3.2 Vertical Axis Wind Turbine (VAWT) ............... 37
2.3.3 VAWT Operating Requirements ..................... 38
2.3.4 Advantages and Disadvantages of VAWTs ........... 38
2.3.5 Operational Difficulties of VAWTs ............... 39
2.3.6 Simplified Procedure for Predicting Darrieus
Wind Turbine Performance ........................ 39
2.3.7 Understanding Flow Phenomena of VAWTs ........... 39
2.3.8 Early European Wind Turbines .................... 40
2.4 Off-Design Performance ................................. 40
2.4.1 Critical Design Aspects ......................... 41
2.4.2 Impacts of Variations in Design and Operating
Parameters ...................................... 41
2.4.3 Impact of Drag and Lift Coefficients on
Maximum Power Coefficient ....................... 41
2.4.4 Performance Enhancement Schemes ................. 42
2.5 Techniques for Capturing Large Amounts of Wind
Energy ................................................. 43
2.5.1 Impacts of Blade and Angle Parameters on
Performance Capabilities ........................ 45
2.5.2 Techniques for Achieving High Power
Coefficients .................................... 47
2.5.3 Installation Site Requirements for Optimum
Performance ..................................... 47
2.5.3.1 Wind Parameters over Ridges and
Hills .................................. 48
2.5.3.2 Variations in Wind Speed and
Direction .............................. 50
2.5.4 Fundamental Properties of Wind Energy ........... 50
2.5.4.1 Available Wind Power ................... 51
2.5.4.2 Power Generated from Wind Energy ....... 51
2.5.4.3 Impacts of Wind Speed and
Installation Height on Performance ..... 55
2.5.5 Global Wind Power Capacity Using High-Power
Turbines ........................................ 57
2.6 Annual Energy Acquisition from Specified Wind Turbine
Site ................................................... 58
2.6.1 Requirements for Long-Term Capture of Wind
Energy .......................................... 59
2.6.2 Impact of Wind Speed on Wind Energy Density ..... 59
2.6.3 Annual and Hourly Extraction of Wind Energy by
Wind Turbine .................................... 60
2.6.4 Energy Integrals for Savonius Rotor in VAWT ..... 60
2.6.5 Use of Vortices for Creating Regions of High
Wind Velocity ................................... 61
2.6.6 Maximum Power Coefficient as Function of Exit
Pressure Coefficient and Interference Factor
(a) ............................................. 62
2.6.7 Computations of Power Coefficients .............. 62
2.6.7.1 Techniques for Enhancing Power Output
2.7 Estimating Annual Hours of Capturing Wind Energy ....... 64
2.7.1 Annual Hours Estimation Using Empirical
Method .......................................... 64
2.7.2 Annual Energy Production Estimate Using Blade
Element Momentum Method ......................... 67
2.7.3 Parameters Affecting Performance ................ 71
2.7.3.1 Impact of Wind Characteristics on
Power Coefficient ...................... 71
2.7.4 Combined Impact of Rotor Tip Speed Ratio and
Drag-to-Lift Ratio on Power Coefficient ......... 75
2.8 Summary ................................................ 77
References .................................................. 78
3 Design Aspects and Performance Capabilities of Wind
Turbine Rotors .............................................. 79
3.1 Introduction ........................................... 79
3.1.1 Rotor Types and Their Performance
Capabilities .................................... 80
3.1.1.1 Rotor Blades ........................... 80
3.2 One-Dimensional Theory for Ideal Rotor ................. 80
3.2.1 Axial Momentum Equation in Integral Format ...... 82
3.2.2 One-Dimensional Momentum Theory Using
Alternate Control Volume ........................ 84
3.2.3 Power Coefficient for Ideal One-Dimensional
Wind Turbine .................................... 86
3.2.4 Thrust Coefficient for Ideal One-Dimensional
Wind Turbine .................................... 86
3.2.5 Effects of Rotation ............................. 90
3.2.6 Tip Speed Ratio of Rotor ........................ 92
3.2.6.1 Properties of Airfoils ................. 94
3.3 Two-Dimensional Aerodynamic Model ...................... 97
3.3.1 Airfoil Configuration for Two-Dimensional
Aerodynamic Model ............................... 97
3.4 Three-Dimensional Aerodynamic Model for Wing of
Finite Length .......................................... 98
3.4.1 Parameters Affected by Streamlines Flowing
over Wing ....................................... 99
3.4.2 Coriolis and Centrifugal Forces ................ 100
3.4.3 Vortex System behind Modern Wind Turbine ....... 101
3.5 Rotor Design Requirements for Wind Farm
Applications .......................................... 102
3.5.1 Rotor Performance .............................. 102
3.5.2 Material Requirements for Rotor Blades ......... 103
3.5.3 Impacts of Airfoil Characteristics on Rotor
Performance .................................... 104
3.6 Hydrodynamic Analysis of Flow over Rotor .............. 104
3.6.1 Two-Dimensional Flow Analysis over Sphere ...... 104
3.6.2 Two-Dimensional Flow Analysis over Cylinder .... 105
3.6.3 Power Generated by Windstream .................. 107
3.7 Summary ............................................... 107
References ................................................. 109
4 Wind Turbine Blade Design Requirements ..................... 111
4.1 Introduction .......................................... 111
4.2 Analysis of Performance of Propeller Blades ........... 112
4.2.1 Aerodynamic Performance Analysis of Blade
Elements ....................................... 112
4.2.2 Thrust and Power on Annul#f Area of Blade ...... 114
4.2.3 Conditions for Maximum Power Output ............ 115
4.3 Blade Performance ..................................... 116
4.3.1 Power Coefficient .............................. 116
4.3.2 Axial Interference Factor ...................... 116
4.3.3 Torque Grading Coefficient ..................... 117
4.3.4 Blade Loading Coefficient ...................... 118
4.3.5 Variations of Flow Angle as Function of
Tangential Speed Ratio and Flow Angle .......... 120
4.3.6 Impact of Tip Speed Ratio and Drag-to-Lift
Coefficient on Wind Turbine Power
Coefficient .................................... 121
4.3.7 Variations in Pitch Angle as Functions of
Radius ......................................... 122
4.3.8 Forces Acting on Blades ........................ 124
4.3.9 Mechanical Integrity ........................... 125
4.3.9.1 Structural Parameters and Stresses .... 125
4.3.9.2 Shearing Forces and Bending Moments
in Presence of External Forces ........ 128
4.4 Application of Beam Theory to Various Turbine Blade
Configurations ........................................ 130
4.5 Material Requirements for Blades ...................... 130
4.6 Critical Features of Blade Section .................... 130
4.6.1 Impacts of Bending Moments and Blade
Instability on Performance ..................... 131
4.6.2 Role of Wind Triangle .......................... 131
4.7 Summary ............................................... 133
References ................................................. 134
5 Sensors and Control Devices Required for Dynamic
Stability and Improved Performance under Variable Wind
Environments ............................................... 137
5.1 Introduction .......................................... 137
5.2 Regulation Control Systems ............................ 139
5.2.1 Pitch Regulation Control ....................... 140
5.2.2 Description of Pitch Regulation Control
System ......................................... 141
5.2.3 Yaw Control System ............................. 142
5.3 Sensors for Monitoring Wind Parameters ................ 143
5.4 Transmission Systems .................................. 143
5.5 Electrical Generators ................................. 144
5.5.1 Induction Generators ........................... 144
5.5.2 Rotor Configurations for Induction
Generators ..................................... 145
5.6 Performance Capabilities and Limitations of
Synchronous Generators ................................ 145
5.7 Critical Rotor Performance Parameters ................. 146
5.7.1 Rotor Design Classifications ................... 147
5.7.2 Dynamic Stability and Structural Integrity ..... 147
5.7.3 Monitoring of Stress Parameters ................ 149
5.7.4 Stall Regulated Rotors ......................... 149
5.7.5 Factors Affecting Wind Energy Capture and
Turbine Performance ............................ 149
5.8 Impacts of Airfoil Characteristics on Blade and
Turbine Performance ................................... 151
5.8.1 Vortex System behind High-Capacity Turbine ..... 152
5.9 Automatic Shut-Down Capability ........................ 152
5.10 Critical Design Aspects of HAWT and VAWT Rotors ....... 153
5.10.1 Techniques for Improving Turbine Reliability
and Performance ................................ 153
5.10.2 Sensors for Ensuring Efficiency, Dynamic
Stability, and Structural Integrity ............ 154
5.10.3 Blade Twist Angle Adjustments .................. 156
5.11 Low Harmonic Content Electrical Generators for
Improving Efficiency .................................. 156
5.11.1 Bearing Reliability ............................ 156
5.12 Impacts of Loadings on Structural Integrity of Wind
Turbine ............................................... 157
5.12.1 Impact of Gravitational Loading ................ 157
5.12.2 Impact of Inertial Loading ..................... 157
5.12.3 Impact of Aerodynamic Loading .................. 159
5.13 Summary ............................................... 160
References ................................................. 161
6 Stand-Alone Wind Turbine Systems ........................... 163
6.1 Introduction .......................................... 163
6.2 Historical Background: Use at Remote Sites ............ 165
6.3 Configurations of Stand-Alone Systems ................. 166
6.3.1 Hybrid System with Back-Up Capability .......... 166
6.3.2 Micro Wind Turbines ............................ 167
6.3.3 Applications of Micro Wind Turbines ............ 167
6.3.4 Micro Wind Turbines for Rural
Electrification ................................ 168
6.3.5 Power Generating Capacity ...................... 169
6.3.6 Telecommunications Applications in Remote
Areas .......................................... 169
6.3.7 Cost Reduction Techniques ...................... 170
6.3.8 Reducing Power Demands ......................... 170
6.3.9 Typical Energy Consumption by Electrical
Appliances ..................................... 170
6.3.10 Techniques for Reducing Energy Consumption ..... 171
6.4 Stand-Alone Systems for Remote Sites .................. 171
6.4.1 Refrigeration Appliances ....................... 173
6.4.2 Air Conditioning Units ......................... 173
6.4.3 Selection of AC or DC Operation ................ 174
6.4.4 Parameters of Generating System ................ 175
6.5 Sizing of System Components ........................... 175
6.5.1 Sizing and Performance Capabilities of Solar
Arrays ......................................... 176
6.5.2 Sizing and Performance Capabilities of
Inverters ...................................... 176
6.5.3 Sizing and Performance Parameters of
Batteries ...................................... 178
6.5.4 Sizing and Performance Parameters of Solar
Panels ......................................... 179
6.6 Stand-Alone Systems with Utility Power Back-Up ........ 179
6.6.1 Economic Aspects of Remote Systems ............. 181
6.6.2 Cost Analysis for Stand-Alone Hybrid System .... 181
6.6.3 Cost Estimate for Extending Line from
Existing Utility ............................... 182
6.7 Stand-Alone Wind Turbine-Based Systems for Various
Applications .......................................... 182
6.7.1 Telecommunications ............................. 183
6.7.2 Performance Capabilities of HR 3 Hybrid ........ 183
6.7.3 Fuel Savings from Use of Hybrid Systems ........ 184
6.8 Hybrid Systems for Village Electrification ............ 185
6.8.1 Successful Examples ............................ 185
6.8.2 Application of Village Electrification for
Water Pumping .................................. 186
6.8.3 Estimating Pumping Capacity of Farm Windmill ... 187
6.8.4 Hybrid Wind Turbines for Economic
Electrification ................................ 188
6.9 Multitasking Wind Turbines ............................ 188
6.9.1 Low-Power Turbine Applications ................. 189
6.9.2 Design Requirements for Irrigation ............. 190
6.9.3 Annual Energy Outputs of Wind Turbines ......... 190
6.9.3.1 Wind Power Density and AEO
Computations .......................... 191
6.10 Summary ............................................... 192
References ............................................ 194
7 Wind Energy Conversion Techniques in Built
Environments ............................................... 195
7.1 Introduction .......................................... 195
7.2 Concentrator Configuration Requirements ............... 196
7.2.1 Sphere-Like Configuration ...................... 196
7.2.2 In-Ducts-through-Buildings Configuration ....... 196
7.2.3 Close-to-a-Building Configuration .............. 197
7.2.4 Capabilities of Various Concentrator Schemes:
Summary .................................................... 197
7.3 Energy Design Buildings ............................... 197
7.3.1 Requirements for Built Environments ............ 197
7.3.2 Impact of Roughness Length on Wind Speed
Parameters ..................................... 199
7.3.2.1 Estimating Wind Speed in City
Environment ........................... 200
7.3.3 Wind Potential in Built Environments ........... 202
7.3.3.1 Atmospheric Boundary Layers ........... 202
7.3.3.2 Impact of Atmospheric Boundary Layer
on Wind Speed and Variations .......... 203
7.3.3.3 Vertical Wind Speed Gradient .......... 203
Local Wind Characteristics in Built Environments ...... 207
7.4.1 Building Characterization ...................... 207
7.4.2 Streamlines around Buildings with Sharp
Edges .......................................... 208
7.4.3 E)rag Force Components ......................... 208
7.4.4 Air Flow Properties ............................ 209
7.4.4.1 Hydrodynamic Analysis of Flow over
Sphere ................................ 210
7.4.4.2 Impact of Pressure Coefficient on
Free Stream Quantities ................ 211
7.4.4.3 Theoretical Aspects of Reynolds and
Strouhal Numbers ...................... 212
7.4.3.4 Probability Function of Wind Speed
for BAWT Installations ................ 214
Impact of Built Environment on BAWT Performance ....... 215
7.5.1 Aerodynamic Noise Levels ....................... 215
7.5.2 Computation of Total Aerodynamic Noise at
Installation Site .............................. 215
7.5.3 Noise Arising from Nearby Wind Turbines ........ 216
7.5.4 Induced Vibrations from Turbine Blades ......... 218
7.5.5 Shadow Flicker from Blades ..................... 218
7.5.6 Turbulent Structures ........................... 219
7.5.7 Impact of Stream Tube Length on Wind Energy
Extraction ..................................... 220
7.5.8 Yawed Flow Requirements in Built Environment ... 221
7.5.8.1 Rotor Design Configurations for
BAWT Systems .......................... 221
7.5.8.2 Drag-Driven Wind Turbine .............. 221
7.5.8.3 Lift-Driven Wind Turbine .............. 223
7.5.8.4 Deceleration of Air by Rotor .......... 224
7.5.8.5 Power Absorbed by Actuator ............ 225
7.5.8.6 Hybrid-Driven Wind Turbines ........... 226
7.5-8.7 Comparison of Wind Turbines in
Built Environments .................... 226
7.5.8.8 Boundary Conditions for Wind
Turbines in Built Environments ........ 227
7.6 Summary ............................................... 227
References ............................................ 228
8 Environmental Issues and Economic Factors Affecting Wind
Turbine Installation ....................................... 229
8.1 Introduction .......................................... 229
8.2 Environmental Factors and Other Critical Issues ....... 230
8.2.1 Choice of Installation Site .................... 230
8.2.2 Wind Features and Their Effects ................ 231
8.2.3 Terrain Modifications to Augment Wind Speeds
for Improved Performance ....................... 232
8.2.4 Impact of Volumetric Flow Rate on
Performance .................................... 233
8.2.5 Maximum Extractable Power ...................... 234
8.2.6 Power Coefficient .............................. 234
8.2.7 Output Torque Performance ...................... 235
8.2.8 Power Generated by Windstream as Function of
Windstream Diameter ............................ 238
8.3 Problems Arising from Large Windstream Diameters ...... 238
8.3.1 Higher Noise Levels ............................ 239
8.3.2 Ambient Noise from Installation Site ........... 241
8.3.2.1 Estimating Noise Levels from Wind
Turbines .............................. 241
8.3.2.2 Community Reaction to Wind Turbine
Noise ................................. 242
8.3.3 Television and Radio Interference .............. 242
8.3.4 Quantitative Description of Wind Turbine
Noise .......................................... 242
8.3.4.1 Estimation of Noise Generated by
Single, High-Capacity Wind Turbine .... 245
8.4 Estimating Critical Performance Parameters Using
Classical BEM Theory .................................. 247
8.4.1 Mechanical Shaft Power ......................... 247
8.4.2 Impact of Blade Design Parameters on
Performance Level .............................. 248
8.5 Justification of Wind Turbine Installation Based on
Economics ............................................. 248
8.5.1 Continuous Availability of Electrical Energy ... 249
8.5.2 Estimating Procurement Costs ................... 250
8.5.3 Per-Kilowatt Electrical Energy Cost ............ 250
8.5.4 Per-Kilowatt Electrical Energy Cost from Wind
Turbine ........................................ 251
8.5.4.1 Empirical Method for Computing
Annual Energy Output of Wind
Turbine ............................... 251
8.5.4.2 Cost of Electricity as Function of
Turbine Cost and Life ................. 252
8.5.4.3 More Elaborate Method of Computing
Cost of Energy Generated by Wind
Turbine ............................... 253
8.5.4.4 Sample Calculation for Estimating
Cost of Electricity Generated by
Wind Turbines ......................... 254
8.6 Estimated Costs of Critical Components and
Subsystems ............................................ 255
8.6.1 Cost Estimates for Critical Components ......... 255
8.6.2 Typical Design and Performance
Characteristics of 2-MW Wind Turbine ........... 257
8.7 Wind Turbine Towers ................................... 257
8.7.1 Tower Height Requirements ...................... 258
8.7.2 Mechanical Strength Requirements ............... 258
8.7.3 Tower Classifications .......................... 258
8.8 Summary ............................................... 259
References ................................................. 260
Index ......................................................... 261
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