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/yrin 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 TurbinesDrag Systems

Vertical Axis HorizontalAxis

1

2

3

Darrieus

‘H’ Rotor

Aerodynamic Systems

Savonius

Drag w/ Windbreak

Cp-max ~0.2Cp-max ~0.44

Modern System Components

Rotor Blades: Materials

Rotor Speed ControlActive Stall Control Passive Stall Control

Advantages: dynamic, reduces train complexityDisadvantages: costly, more complex

Advantages: Simple, self regulatingDisadvantages: 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

221' vv

v

AvP 310 2

1

2122

214

1vvvvAP

Due to Albert Betz

• Continuity, energy balance, and force balance across rotor area

• Key Results:

Ideal Extractor Derivation

593.027

16~

112

1

max

1

2

2

1

2

0

p

p

C

v

v

v

v

P

PC

• 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

1v

RA

Blade Pitch: Trade-offs

Since most designs use twisted blades, power quality is neverideal 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 Blades 34.0% 21.0%

Rotor hubBlade bearingsHydraulic blade-pitch systemRotor shaftRotor bearings with housingsGearboxLoad-bearing nacelle structureYaw drive (including azimuth bearings)Nacelle fairingMiscellaneous (rotor brake, clutches, etc.)

2%--

0.8%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%

Tower 16.4% 20.7%

Component Costs 100.0% 100.0%

Assembly (in the factory) 5.0% 5.0%

Economics of Wind Power 2

Economics of Wind Power 3

• 6-9 cents / kWh!!!• Roughly competitive

with current pricesTech innovations:• Innovative drive trains• Less than 3 blades• Reducing mass in

vertical-axis turbinesEvolution 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