Wind Power: Fundamentals, Technologies, and Economics Norman Horn and Tony VanderHeyden

History of Wind Power From… and… to…

World Capacity for Wind Power Solar energy produces the large-scale motion of the atmosphere and winds Differential heating causes minor fluctuations Coriolis acceleration Power in wind  cube of velocity World Energy Council estimated 20,000 TWh/yr in potential wind power

United States Annual Average Wind Power

United States Installed Capacity

Altamont Pass: Over 6,000 Turbines!

Texas Wind Power Texas is the leader in wind power in the United States (ahead of California!) – Nearly 4,000 MW installed in 2007 – Goal of over 25,000 MW by 2012 Horse Hollow Wind Farm – 735 MW capacity – 47,000 acres – 421 total turbines Horse Hollow Wind Farm

Types of Wind Turbines Drag Systems Vertical Axis Horizontal Axis Darrieus ‘H’ Rotor Aerodynamic Systems Savonius Drag w/ Windbreak Cp-max ~0.2 Cp-max ~0.44

Modern System Components

Rotor Blades: Materials

Rotor Speed Control Active Stall ControlPassive Stall Control Advantages: dynamic, reduces train complexity Disadvantages: costly, more complex Advantages: Simple, self regulating Disadvantages: requires strength in high winds, hard to start-up, complex brake systems

Where should we put all the stuff? Situation dependent Maintenance requirements Size Wind quality Budget

Ideal Extractor Derivation Due to Albert Betz Continuity, energy balance, and force balance across rotor area Key Results:

Ideal Extractor Derivation Irrotational system No boundary layer or compression flow Creeping flow (Re << 1) Uniform power extraction No geometry boundary conditions Never true!

More Rigor: Deviation from Betz Limit

Blade Pitch: Trade-offs Since most designs use twisted blades, power quality is never ideal across the entire rotor blade.

More Cp, or “Why you should choose three blades too”

Technological Challenges Integrating unpredictable energy resources into existing power systems / grids. Accurate estimation of wind resources – Location, location, location! Not a commodity, a custom product. Scaling up, scaling down… Energy storage?

Location and Grid Connection Avg. wind speed of over 10 mph required – Ideal location: near constant flow of non- turbulent wind, minimal fluctuations & gusts Critically important to have accurate wind speed and direction data – Overestimating wind  massive loss of profit “Wind park effect” loss (as low as 2%) How far away is the grid? – Capital costs of any connection is substantial

Environmental and Social Concerns Pollution? Virtually none… What about construction? – Actual Average EROI: 18 – Net energy gain: between 17 and 39 Birds? Studies have been published with contradictory results… – Negligible harm compared to other human activity Noise? Wind power noise is far less than most other human activity. – Does off-shore wind technology affect marine life? Aesthetics and safety? – Offshore wind farms can reduce aesthetics complaints. – Wind energy has an excellent safety record.

Economics of Wind Power 1 Wind Turbine Components Medium-sized turbine: 750 kW (stall-controlled) Proportion % Large turbine: 1500 kW (variable- speed controlled) Proportion % Rotor Blades34.0%21.0% Rotor hub Blade bearings Hydraulic blade-pitch system Rotor shaft Rotor bearings with housings Gearbox Load-bearing nacelle structure Yaw drive (including azimuth bearings) Nacelle fairing Miscellaneous (rotor brake, clutches, etc.) 2% % 2.7% 1.0% 12.5% 8.7% 2.4% 2.0% 5.0% 2.1% 3.1% 4.0% 2.6% 1.7% 13.6% 4.7% 3.4% 1.6% 3.2% Generator (and inverter for large turbine) Control system and monitoring equipment 7.5% 5.0% 10.9% 7.4% Tower16.4%20.7% Component Costs100.0% Assembly (in the factory)5.0%

Economics of Wind Power 2

Economics of Wind Power cents / kWh!!! Roughly competitive with current prices Tech innovations: Innovative drive trains Less than 3 blades Reducing mass in vertical-axis turbines Evolution of technology

Advantages of Wind Power After installation, only cost is maintenance Wind is renewable Available everywhere to some extent No pollution Simple designs Supply of wind energy cannot be controlled by anyone (no political maneuvering) Wind farms make it profitable

Disadvantages of Wind Power Expensive to set up, custom products Wind speed varies a lot – Hard to predict – Not steady, so unreliable – Accurate data absolutely necessary Environmental impact from manufacturing Turbines can require large areas of land

Gearbox Design Decisions

Generator Design Considerations Other Factors: Weight Starting overcurrent Dynamic response behavior Speed range

Dirt and bug juice: The enemy