Wind Energy Meteorology
Description
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.
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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.
Content
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
3.7.2 Vertical Profiles of Wind and Turbulence . . . . . . . . . . . 653.7.3 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
4.1.2 Katabatic Winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 804.2 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
4.4 Terrain ruggedness4.5 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
6.2.3 Analytical Model for Wind Park Wakes . . . . . . . . . . . . . . . . . . 1446.2.4 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
7.1.4 Satellite data7.1.5 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
7.2.2.2 Reanalysis data7.2.2.3 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
10.6 Repercussions of Large-Scale Wind Power Extraction on Weather and Climate. . . .158References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193