1. Wind Turbine Design Methods
Robert Scott
November 1, 2007

2. Advantages of Wind Power
Clean
Flexible
Large Potential for Growth
Economically Viable (most of the time – peak opportunity)

3. Design
Siting
Configurations
Sizing
Rotor
Tower
Generator

4. Siting Wind speed Climate Conditions Inland or at sea Terrain
Surrounding Community

5. Configurations Vertical Axis Disadvantages Darrieus H-Type Savonius
Size limits
Reliability

6. Configurations Horizontal Axis
3-bladed most common, structures and dynamic considerations
1 and 2-bladed designs exist, but don’t even bother.
Upwind or Downwind

7. Sizing Designs exist for capacities of <1 kW up to 5 MW.
What are you designing for?
Utilities
Individual Use
Special Use

8. Rotor Diameter Blades Control
Larger = higher capacity and higher costs, helps for lower windspeed
Blades
Airfoils
Shape (Twist)
Control
Stall/Pitch regulated
Rotational Speed

9. Rotor Control Stall/Pitch regulated Rotational Speed
Cut-in, rated, cut-out velocities

10. Tower Type Height Tubular Lattice Tall = smoother air
Short = better for construction

11. Wind Variability The terrain of the site affects the wind speed.
Higher roughness lengths slow the wind down more at low elevations.

12. Generator
Enclosed?
Gearbox?
Direct-drive?

13. Design Process Performance Economics Efficiency Reliability
Infrastructure (~ $1.7 Million per MW)
Construction
Operational Costs (~ 2% of acquisition costs/yr)
Subsidies

14. The Power Curve Published power curve for a 1.5 megawatt wind turbine.
Nordex S70. Vc-o≈ 2VR

15. Wind Variability Model the wind as a probability density function
The Weibull distribution
For wind,

16. What does all this tell us?
Capacity Factor:
A capacity factor of 35% for a wind turbine is considered good.
Ū = 5 m/s  CF = 0.05
Ū = 7 m/s  CF = 0.18
Ū = 9 m/s  CF = 0.42
Ū = 11 m/s  CF = 0.73

17. Sensitivity Studies – HOMER
Sensitivity to wind speed
Ū = 5 m/s:
225,000K $0.15/kWh
Ū = 14 m/s:
1,000,000K $0.055/kWh
Sensitivity to hub height
zH = 40 m
500,000K $0.087/kWh
Ū = 5 m/s:
675,000K $0.07/kWh

18. The Power Coefficient
The power output normalized to the energy density of the wind and the rotor area.
Measures the amount of power actually converted out of the power available in the wind

19. Optimized Costs of Energy
Optimized Cost of Energy:
$0.038/kWh (3% interest)
$0.040/kWh (4% interest)
$0.042/kWh (5% interest)
$0.044/kWh (6% interest)
High wind speed areas, U > 10 m/s consistently
Maximized hub heights, zH = 100 m
Large development – Economies of scale reduce per unit price of turbines.
Comparison with other fuels:
Coal $0.02 – 0.03/kWh
Natural Gas $0.05 – 0.08/kWh
Nuclear $0.02 – 0.03/kWh
Note: Other fuels, especially coal and nuclear, benefit from not having to include their high external costs in the price of energy. Wind energy also receives a $0.015/kWh tax credit.

20. Useful Websites
List of wind farms:
Wind turbine Manufacturers
Current Events