Wind Resource Assessment and Micro-siting

Matthew Huaiquan Zhang, Independent Renewable Energy Consultant, China/ UK

Preface xiii Introduction xv

Acknowledgments xvii

About the Author xix

List of Symbols xxi

1 Introduction 1

1.1 Wind Resource Assessment as a Discipline 2

1.2 Micro-siting Briefing 2

1.3 Cascade of Wind Regime 3

1.3.1 Global Scale Wind Regime 3

1.3.2 Synoptic Scale Wind Regime 5

1.3.3 Meso-scale Wind Regime 5

1.3.4 Local Scale Wind Regime 6

1.4 Uncertainty of Wind Resource 7

1.5 Scope of the Book 9

References 9

2 Concepts and Analytical Tools 11

2.1 Surface Roughness and Wind Profile 11

2.1.1 Roughness Length 11

2.1.2 Vertical Wind Profile 14

2.1.3 Internal Boundary Layer 15

2.1.4 Roughness Change Model 16

2.1.5 Displacement Height 17

2.1.6 Wind Shear 18

2.2 Speed-up Effect of Terrain 20

2.2.1 Horizontal Speed-up Profile 20

2.2.2 Vertical Speed-up on Hill Top 22

2.2.3 Orographic Categorisation of Terrain 24

2.2.4 Ruggedness Index 27

2.3 Shelter Effect of Obstacles 28

2.3.1 Reduced Wind Speed 29

2.3.2 Increased Turbulence Intensity 31

2.4 Summary 32

References 33

3 Numerical Wind Flow Modelling 35

3.1 Modelling Concept Review 36

3.1.1 Wind Flow Concepts 36

3.1.2 Governing Equations 37

3.1.3 Meshing the Computational Domain 41

3.2 Linearised Numerical Flow Models 42

3.2.1 Jackson–Hunt Model 42

3.2.2 WAsP Model: The Principle 43

3.2.3 WAsP Model: Limitations 46

3.2.4 WAsP Model: Improving the Results 48

3.3 Mass-Consistent Models 50

3.4 CFD Models 50

3.4.1 Meteodyn WT and WindSim 51

3.4.2 Validation of CFD models 52

3.5 Meso Scale NWP Models 53

3.6 Inherent Uncertainties in Wind Flow Modelling 55

3.7 Summary 56

References 56

4 Wind Park Physics and Micro-siting 61

4.1 Wind Power Density 61

4.2 Wind Power Conversion 63

4.2.1 Betz’s Limit 63

4.2.2 Power Coefficient 65

4.2.3 Thrust Coefficient 65

4.2.4 Wind Turbine Power Curve 66

4.2.5 Power Curve Adjustment 67

4.3 Wind Turbine Wake Effects 68

4.3.1 Analytical Structure of Wake 68

4.3.2 Reduced Velocity Wake Models 70

4.3.3 Added Turbulence Wake Models 73

4.3.4 Deep Array Wake Models 75

4.3.5 Wake Effects in Complex Terrain 77

4.4 Wind Turbine Micro-siting 78

4.4.1 Park Efficiency 79

4.4.2 Capacity Factor 80

4.4.3 Site-Specific Wind Conditions 80

4.4.4 Wind Turbine Selection 82

4.4.5 Site Survey 83

4.4.6 Wind Sector Management 86

4.5 Summary 87

References 87

5 Wind Statistics 91

5.1 Statistics Concepts Review 91

5.1.1 Random Variables 91

5.1.2 Sample Mean and Standard Deviation 92

5.1.3 Probability Density Distribution 92

5.2 Wind Data Time Series 93

5.2.1 Mean Wind Speed 94

5.2.2 Turbulence Intensity 95

5.2.3 Wind Direction 97

5.3 Mean Wind Speed of the Whole Time Series 99

5.4 Weibull Distribution 100

5.4.1 Weibull Probability Density Function 100

5.4.2 Weibull Cumulative Distribution Function 101

5.4.3 Rayleigh Distribution 103

5.5 Estimating Weibull Parameters 104

5.5.1 Linear Regression Method 104

5.5.2 Mean-Standard Deviation Method 105

5.5.3 Maximum Likelihood Estimate Method 105

5.5.4 Medians Method 106

5.5.5 Power Density Method 107

5.5.6 Quality of the Weibull Fit 108

5.6 Extreme Wind Statistics 110

5.6.1 Independent Extreme Wind Events 110

5.6.2 Gumbel Method 111

5.6.3 Peaks-Over-Threshold Method 116

5.6.4 Extreme Wind Gusts 117

5.7 Summary 118

References 118

6 Measure–Correlate–Predict 121

6.1 Wind Data Correlation 122

6.1.1 Correlation Coefficient 122

6.1.2 Physical Interpretations of the Correlation 122

6.1.3 The Impact of Averaging Interval 123

6.2 Wind Data Regression and Prediction 125

6.2.1 Regression Equation and Residual 125

6.2.2 Data Validation 127

6.2.3 Data Resampling 128

6.3 MCP Methodology for Wind Energy 129

6.3.1 Linear Regression 129

6.3.2 Variance Ratio Method 130

6.3.3 Weibull Scale Method 131

6.3.4 Mortimer Method 132

6.3.5 WindPRO Matrix Method 132

6.3.6 Artificial Neural Networks 134

6.4 MCP Uncertainty 135

6.4.1 Reducing MCP Uncertainty 135

6.4.2 Estimating MCP Uncertainty 135

6.4.3 Overlapping Period 136

6.5 Sources of Reference Data 137

6.5.1 Meteorological Stations 137

6.5.2 Reanalysis Data 138

6.6 Summary 139

References 140

7 Wind Park Production Estimate 143

7.1 Gross and Net AEP 143

7.1.1 Wake Losses 144

7.1.2 Availability Losses 145

7.1.3 Power Curve Performance 145

7.1.4 Environmental Losses 146

7.1.5 Electrical Losses 147

7.1.6 Curtailments 147

7.2 AEP Uncertainty Analysis 148

7.2.1 Defining Uncertainty 148

7.2.2 Combining Uncertainties 150

7.2.3 From Wind Speed Uncertainty to AEP Uncertainty 151

7.2.4 P90, P75 and P50 AEP 151

7.3 Natural Variability of Wind 153

7.3.1 Inter-Annual Wind Speed Variability 153

7.3.2 Long-Term Stability of Windiness 154

7.4 Uncertainty in Wind Measurement 155

7.5 Uncertainty in Wind Flow Modelling 156

7.5.1 Vertical Extrapolation 156

7.5.2 Horizontal Extrapolation 158

7.5.3 Wind Resource Similarity 159

7.5.4 Deploying Multiple Masts 160

7.6 A Case Study 162

7.7 Wind Resource Assessment Report 163

7.8 Summary 165

References 166

8 Measuring theWind 169

8.1 Representativeness of the Met Mast 169

8.1.1 Similar Wind Climate 170

8.1.2 Similar Topography 172

8.1.3 Similar Shelter Effect 172

8.2 Cup Anemometer Physics 173

8.2.1 Horizontal Wind Speed 174

8.2.2 Vertical Sensitivity 174

8.2.3 Dynamic Response in Turbulent Winds 175

8.2.4 Nonlinearity and Mechanical Friction 177

8.2.5 Sheared Flow Effect 178

8.2.6 Cup Anemometer Design 178

8.3 Met Mast Installation 179

8.3.1 Tower Shadow 179

8.3.2 Boom and Ancillary Effect 181

8.3.3 Wind Direction Vane 181

8.3.4 Air Temperature and Other Parameters 183

8.3.5 Good Practice 183

8.4 Met Mast Operation and Maintenance 185

8.4.1 Documentation 185

8.4.2 On-Site Inspection 188

8.4.3 Monitoring 189

8.5 Data Validation 190

8.5.1 Test Criteria 190

8.5.2 Graphical Review 191

8.5.3 Combining the Data 191

8.5.4 Data Recovery Rate 192

8.6 Alternative Wind Sensors 192

8.6.1 Propeller Anemometer 192

8.6.2 Sonic Anemometer 193

8.6.3 Sodar 195

8.6.4 Lidar 196

8.6.5 Deploying Sodar and Lidar 197

8.7 Summary 199

References 200

9 Atmospheric Circulation and Wind Systems 201

9.1 General Concepts 201

9.1.1 Vertical Structure of the Atmosphere 201

9.1.2 Standard Atmosphere 203

9.1.3 Geopotential Height and Sigma Height 203

9.1.4 Cascade of Scales 204

9.2 Laws and Driving Forces 206

9.2.1 Equation of State 206

9.2.2 Hydrostatic Equation 206

9.2.3 Air Density 207

9.2.4 Forces and Winds 208

9.3 General Atmospheric Circulations 210

9.3.1 Geostrophic Winds 210

9.3.2 Baroclinic Atmosphere and Thermal Winds 211

9.3.3 Three Cell Circulation 212

9.4 Synoptic Scale Wind Systems 214

9.4.1 Mid-latitude Cyclones and Anticyclones 214

9.4.2 Weather Fronts 215

9.4.3 Tropical Storms 216

9.5 Meso-scale Wind Systems 217

9.5.1 Convection and Thunderstorms 218

9.5.2 Land and Sea Breezes 219

9.5.3 Mountain and Valley Winds 221

9.5.4 Katabatic Winds 222

9.6 Micro-scale Winds 222

9.6.1 Turbulence Kinetic Energy 223

9.6.2 Turbulent Flux 224

9.6.3 Turbulence Spectra 225

9.7 Summary 226

References 227

10 Boundary Layer Winds 229

10.1 Atmospheric Stability 229

10.1.1 Neutral Stratification 230

10.1.2 Unstable Stratification 230

10.1.3 Stable Stratification 231

10.1.4 Stability Parameter 231

10.1.5 Modification on a Vertical Wind Profile 232

10.1.6 Influence on Turbulence 233

10.2 Orographic Effects 234

10.2.1 Channelling of Wind 234

10.2.2 Wind Speed-up and the Froude Number 235

10.3 Onshore Boundary Layer Winds 238

10.3.1 Surface Layer 238

10.3.2 Ekman Layer 239

10.3.3 Diurnal Variations 240

10.3.4 Low-Level Jets 241

10.3.5 Internal Boundary Layer 243

10.4 Offshore Boundary Layer Winds 243

10.4.1 Sea Surface Roughness and Wave Influence 244

10.4.2 Marine Atmospheric Stability 245

10.4.3 Annual and Diurnal Variations 245

10.4.4 Offshore Turbulence Intensity 246

10.4.5 Offshore Vertical Wind Profile 246

10.4.6 Offshore Turbine Layout Optimisation 247

10.5 Summary 248

References 248

11 Environmental Impact Assessment 251

11.1 Biological Impacts 251

11.1.1 Birds and Bats 252

11.1.2 Terrestrial Animals 253

11.1.3 Marine Animals 253

11.1.4 Vegetation 254

11.2 Visual Impacts 254

11.2.1 Shadow Flicker 254

11.2.2 Scenery and Aesthetics 256

11.3 Noise Impacts 257

11.3.1 Wind Turbine Noise Curve 257

11.3.2 Sound Propagation 259

11.3.3 Combining Sound Levels 259

11.3.4 Evaluating Noise Levels 261

11.4 Weather and Climate Change 262

11.5 Public Health and Safety 264

11.6 Summary 264

References 265

Appendix I Frequently Used Equations 267

Appendix II IEC Classification of Wind Turbines 269

Appendix III Climate Condition Survey for aWind Farm 271

Appendix IV Useful Websites and Database 275

Index 277