Wind Energy Fundamentals

Engineering Applications and Design
Engineering Materials

Wind Energy
Fundamentals, Resource Analysis and Economics

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Growing energy demand and environmental consciousness have re-evoked human interest in wind energy. As a result, wind is the fastest growing energy source in the world today. Policy frame works and action plans have already been formulated at various corners for meeting at least 20 per cent of the global energy demand with new-renewables by 2010, among which wind is going to be the major player.

In view of the rapid growth of wind industry, Universities, all around the world, have given due emphasis to wind energy technology in their undergraduate and graduate curriculum. These academic programmes attract students from diversified backgrounds, ranging from social science to engineering and technology. Fundamentals of wind energy conversion, which is discussed in the preliminary chapters of this book, have these students as the target group. Advanced resource analysis tools derived and applied are beneficial to academics and researchers working in this area. The Wind Energy Resource Analysis (WERA) software, provided with the book, is an effective tool for wind energy practitioners for assessing the energy potential and simulating turbine performance at prospective sites.

TOC

Preface ........................................ VII
1 Introduction ......................1
1.1 History of wind energy.................3
1.2 Current status and future prospects..............7
References .......................8

2 Basics of Wind Energy Conversion ..............11
2.1 Power available in the wind spectra ............11
2.2 Wind turbine power and torque ............... 14
2.3 Classification of wind turbines ............. 16
2.3.1 Horizontal axis wind turbines ...........17
2.3.2 Vertical axis wind turbines ............ 18
Darrieus rotor ..................19
Savonius rotor .................20
Musgrove rotor .................. 21
2.4 Characteristics of wind rotors ............... 22
2.5 Aerodynamics of wind turbines ...............23
2.5.1 Airfoil ...................................... 23
2.5.2 Aerodynamic theories ..............27
Axial momentum theory .............27
Blade element theory ...............31
Strip theory ..................33
2.6 Rotor design .....................34
2.7 Rotor performance .................... 40
References .......................42

3 Analysis of wind regimes.................45
3.1 The wind........................ 46
3.1.1 Local effects..................47
3.1.2 Wind shear....................47
3.1.3 Turbulence....................50
3.1.4 Acceleration effect.................51
3.1.5 Time variation..................51
3.2 Measurement of wind.................53
3.2.1 Ecological indicators................ 53
3.2.2 Anemometers...................55
Cup anemometer.................55
Propeller anemometer...............56
Pressure plate anemometer.............56
Pressure tube anemometers............ 57
Sonic anemometer................. 58
3.2.3 Wind direction.................61
3.3 Analysis of wind data.................61
3.3.1 Average wind speed...............63
3.3.2 Distribution of wind velocity.............64
3.3.3 Statistical models for wind data analysis.......68
Weibull distribution...............68
Rayleigh distribution................ 78
3.4 Energy estimation of wind regimes............. 80
3.4.1 Weibull based approach...............80
3.4.2 Rayleigh based approach.............84
References........................88

4 Wind energy conversion systems............... 89
4.1 Wind electric generators.................. 90
4.1.1 Tower......................91
4.1.2 Rotor.......................96
4.1.3 Gear box.................... 99
4.1.4 Power regulation.................101
4.1.5 Safety brakes................... 105
4.1.6 Generator...................107
Induction generator................107
Synchronous generator................ 110
4.1.7 Fixed and variable speed operations.......... 112
4.1.8 Grid integration.................. 115
4.2 Wind farms.....................117
4.3 Offshore wind farms.................. 121
4.4 Wind pumps......................124
4.4.1 Wind powered piston pumps.............126
4.4.2 Limitations of wind driven piston pumps.........129
The hysteresis effect.................129
Mismatch between the rotor and pump characteristics... 132
Dynamic loading of the pump’s lift rod....... 133
4.4.3 Double acting pump...............134
4.4.4 Wind driven roto-dynamic pumps...........135
4.4.5 Wind electric pumps.................140
References........................142

5 Performance of wind energy conversion systems....... 145
5.1 Power curve of the wind turbine...............146
5.2 Energy generated by the wind turbine............150
5.2.1 Weibull based approach.............. 150
5.2.2 Rayleigh based approach.............153
5.3 Capacity factor.....................155
5.4 Matching the turbine with wind regime..........159
5.5 Performance of wind powered pumping systems....... 164
5.5.1 Wind driven piston pumps............. 164
5.5.2 Wind driven roto-dynamic pumps.......... 171
5.5.3 Wind electric pumping systems........... 175
References........................177

6 Wind energy and Environment............... 179
6.1 Environmental benefits of wind energy..........180
6.2 Life cycle analysis.................. 182
6.2.1 Net energy analysis................185
6.2.2 Life cycle emission................189
6.3 Environmental problems of wind energy...........193
6.3.1 Avian issues..................193
6.3.2 Noise emission.................196
6.3.3 Visual impact...................202
References........................205

7 Economics of wind energy................. 209
7.1 Factors influencing the wind energy economics........ 210
7.1.1 Site specific factors............... 210
7.1.2 Machine parameters...............212
7.1.3 Energy market..................213
7.1.4 Incentives and exemptions..............214
7.2 The ‘present worth’ approach................ 215
7.3 Cost of wind energy...................220
7.3.1 Initial investment................221
7.3.2 Operation and maintenance costs............ 222
7.2.3 Present value of annual costs.............223
7.4 Benefits of wind energy................225
7.5 Yardsticks of economic merit................ 227
7.5.1 Net present value................ 227
7.5.2 Benefit cost ratio................ 228
7.5.3 Pay back period.................. 229
7.5.4 Internal rate of return................230
7.6 Tax deduction due to investment depreciation........ 233
References........................236