Wind Energy Meteorology (2^nd Ed., Softcover reprint of the original 2nd ed. 2018) Atmospheric Physics for Wind Power Generation Green Energy and Technology Series

This book offers an introduction to the meteorological boundary conditions for power generation from wind ? both onshore and offshore, and provides meteorological information for the planning and running of this important renewable energy source. It includes the derivation of wind laws and wind-profile descriptions, especially those above the logarithmic surface layer, and discusses winds over complex terrains and nocturnal low-level jets. This updated and expanded second edition features new chapters devoted to the efficiency of large wind parks and their wakes and to offshore wind energy.

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Scope of the Book. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Overview of Existing Literature . . . . . . . . . . . . . . . . . . . . . . . 3

1.3 History of Wind Energy Generation. . . . . . . . . . . . . . . . . . . . . 3

1.4 Potential of Wind Energy Generation. . . . . . . . . . . . . . . . . . . . 4

1.5 Present Status of Wind Energy Generation . . . . . . . . . . . . . . . . 5

1.6 Structure of This Book. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2 Wind Regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.1 Global Circulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2 Driving Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2.1 Hydrostatic Equation . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2.2 Momentum Budget Equations for the Wind . . . . . . . . . . 12

2.3 Geostrophic Winds and Gradient Winds. . . . . . . . . . . . . . . . . . 14

2.4 Thermal Winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.5 Boundary Layer Winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.6 Thunderstorm Gusts and Tornados. . . . . . . . . . . . . . . . . . . . . . 18

2.7 Air Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.8          Thermal stratification of the air

2.8.1      The geostrophic drag law

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3 Vertical Profiles Over Flat Terrain. . . . . . . . . . . . . . . . . . . . . . . . 23

3.1 Surface Layer (Prandtl Layer) . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.1.1 Logarithmic Wind Profile . . . . . . . . . . . . . . . . . . . . . . 28

3.1.2 Power Law. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3.1.3 Comparison Between Logarithmic and Power Law . . . . . 33

3.1.4 Vertical Wind Profile with Large Wind Speeds . . . . . . . 40

3.2 Profile Laws Above the Surface Layer. . . . . . . . . . . . . . . . . . . 40

3.2.1 Ekman Layer Equations . . . . . . . . . . . . . . . . . . . . . . . . 41

3.2.2 Inertial Oscillations in the Ekman Layer . . . . . . . . . . . . 42

3.2.3 Vertical Wind Profiles in the Ekman Layer . . . . . . . . . . 42

3.2.4 Unified Description of the Wind Profile for the Boundary Layer . . . . 43

3.3 Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

3.4 Diurnal Variations of the Wind Profile . . . . . . . . . . . . . . . . . . . 50

3.4.1 Vertical Profiles of the Weibull Parameters . . . . . . . . . . 51

3.4.2 Low Level Jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

3.5 Internal Boundary Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

3.6 Wind and Turbulence Profiles Over Forests . . . . . . . . . . . . . . . 61

3.7 Winds in Cities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

3.7.1 Characteristics of Urban Boundary Layers . . . . . . . . . . . 63

3.7.3 Special Flow Phenomena in Urban Canopy Layers . . . . . 67

3.8 Summary for Flat Terrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

4 Winds in Complex Terrain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

4.1 Characteristics of Boundary Layers Over Complex Terrain . . . . 76

4.1.1 Mountain and Valley Winds. . . . . . . . . . . . . . . . . . . . . 78

4.2 Wind Profiles Over a Hill. . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

4.2.1 Potential Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

4.2.2 Modifications to the Potential Flow: Addition of an Inner Layer . . . 83

4.2.3 Modifications to the Potential Flow: Consideration of Thermal Stability . . . 86

4.3 Wind Profiles Over an Escarpment . . . . . . . . . . . . . . . . . . . . . 87

4.5 Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

4.6 Diurnal Variation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

4.7 Summary for Complex Terrain . . . . . . . . . . . . . . . . . . . . . . . . 91

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

5 Offshore Winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

5.1 Characteristics of Marine Boundary Layers . . . . . . . . . . . . . . . 96

5.1.1 Sea Surface Roughness and Drag Coefficient . . . . . . . . . 96

5.1.2 Fetch and Stability Dependent Wave Formation . . . . . . . 101

5.1.3 Extreme Wave Heights . . . . . . . . . . . . . . . . . . . . . . . . 106

5.1.4 Wave Age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

5.1.5 Impact of the Vertical Moisture Profile . . . . . . . . . . . . . 109

5.1.6 Annual and Diurnal Variations . . . . . . . . . . . . . . . . . . . 110

5.2 Vertical Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

5.3 Extreme Wind Speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

5.4 Turbulence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

5.4.1 Turbulence Intensity . . . . . . . . . . . . . . . . . . . . . . . . . . 116

5.4.2 Wind Speed Variances. . . . . . . . . . . . . . . . . . . . . . . . . 120

5.4.3 Turbulence Length Scales and Inclination Angles . . . . . . 122

5.4.4 Gust Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

5.5 Weibull Parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

5.6 Coastal Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

5.6.1 Land and Sea Winds . . . . . . . . . . . . . . . . . . . . . . . . . . 128

5.6.2 Low-Level Jets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

5.7 Summary for Marine Boundary Layers . . . . . . . . . . . . . . . . . . 130

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

6 Physics of Wind Parks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

6.1 Turbine Wakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

6.2          Wind farm wakes

6.2.1      Observations

6.2.2      Analytical Model for Mean Wind Speed in Wind Parks . . . . . . . 138

6.2.4      Application of the Analytical Model with FINO1 Stability Data . . . . .  146

6.3 Risks that a Tornado Hits a Wind Park . . . . . . . . . . . . . . . . . . 147

6.4 Summary for Wind Parks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

7             Wind data sources

7.1          Measurements

7.1.1      In situ measurements

7.1.2      Surface-based remote sensing

7.1.3      Determination of mixing height

7.1.5      Representativity and quality of measured wind data

7.2          Models

7.2.1      Analytical models

7.2.2      Numerical models

7.2.2.1  Forecast models

7.2.2.3  Large eddy simulations

7.2.2.4  CFD models

7.2.2.5  The gap problem between the mesoscale and the microscale

7.3          Statistical tools

7.3.1      Time series analysis

7.3.2      Mean wind speed spectrum and the Weibull distribution

7.3.3      Extreme mean wind speeds and the Gumbel distribution

7.3.4      Extreme gusts

7.3.5      Gust duration and wind acceleration in gusts

7.3.6      Size of turbulence elements

7.3.7      Measure – correlate – predict (MCP)

References

8             Noise generation and noise propagation

8.1          Noise generation

8.2          Noise propagation

References

9             Other meteorological issues

9.1          Icing

9.2          Lightning

9.3          Aerosols, salt, dust

References

10 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

10.1 Size of Wind Turbines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

10.2 Size of Offshore Wind Parks . . . . . . . . . . . . . . . . . . . . . . . . . 156

10.3 Other Techniques of Converting Wind Energy . . . . . . . . . . . . . 156

10.4 New Measurement and Modelling Tools to Assess Wind Conditions . .  156

10.5 Wind Resources and Climate Change . . . . . . . . . . . . . . . . . . . 157

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 

Stefan Emeis is a meteorologist. He received his PhD at the University of Bonn, Germany in 1985 and his habilitation at the University of Karlsruhe, Germany in 1994. He is currently a senior scientist and research group leader at the Institute of Meteorology and Climate Research at the Karlsruhe Institute of Technology in Garmisch-Partenkirchen, Germany and adjunct professor of meteorology at the University of Cologne, Germany. His research interests are the structure and turbulence of the atmospheric boundary layers, surface-based remote sensing of the atmosphere, the meteorological prerequisites for the usage of wind energy and all aspects of climate change.

He is the editor-in-chief of the scientific journal “Meteorologische Zeitschrift” and (co)author of more than 80 scientific papers and of several books.

Discusses the basics of meteorology for wind power generation

Focuses on large wind turbines and wind parks

Covers offshore wind parks

Includes a mathematical treatment of the efficiency of large offshore wind parks