Wind Turbine Design Methods Robert Scott rscott@gatech.edu November 1, 2007

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

Design Siting Configurations Sizing Rotor Tower Generator

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

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

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

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

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

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

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

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

Generator Enclosed? Gearbox? Direct-drive?

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

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

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

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

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

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

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.

Useful Websites List of wind farms: http://www.fplenergy.com/portfolio/contents/portfolio_by_source.shtml Wind turbine Manufacturers http://www.skystreamenergy.com/skystream/ http://www.enercon.de/en/_home.htm http://www.nordex-online.com/en/ http://www.gamesa.es/index.php/en http://www.suzlon.com/ Current Events http://www.cnn.com/2007/TECH/science/10/09/pip.wind.energy/ www.wind-watch.org