l11 - energy sources - wind

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L11Energy Sources: Wind Energy

Course plan Basic concepts of energy and thermodynamics

Fossil fuels

Climate change

Energy sources Nuclear energy

Geothermal energy

Renewable energy sources Water

Wind Biomass

Solar energy

Energy storage and transport

Energy efficiency


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Sustainable Energy Sources

Nuclear energy

Geothermal energy (water heating)

Water energy

Wind energy

Biomass energy

Solar energy

Solar heating Photovoltaic

Wind energy


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Wind speed (mph)

Scale of wind speed


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Wind power duration

Annual wind cycle


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Daily wind cycle


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US wind electricity potential

Wind power V3


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Extracted power: Betz law

Ideal wind machines


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Tip-speed ratio


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Power coefficient of wind turbines

Solidity Factor Defined as the total blade area of the rotor

divided by the swept area normal to the

wind.

A large area of wind to be intercepted by asmall area of blade

low solidity factor

For the purpose of electricity generation

Use low solidity machines such as the two-blade propeller in order to utilize highoperational speeds and achieve high values ofpower coefficient.


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Mechanical stress on wind turbine

Efficiency of wind electricity


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Efficiency values

= 34% for large machines

= 16% for small machines

Large systems are more efficient than small systems!

1.25 MW machine, d = 53m:

late 1930s - 1945


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Forces on the Wind Machine

Centrifugal forces Due to rotating blades

Tend to pull the propeller blades out of their sockets

Vary the pitch-angle of the propeller blades

At a maximum acceptable wind speed, furling velocity Vf,the pitch-angle of the blades should be adjusted so that

zero power is extracted. Or apply mechanical brake.

Gyroscopic forces

Yawing rotation

Blade rotation

Lightweight blades

Vibrations

Recent wind machines


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Recent wind machines

2 MW wind machine


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3 MW machine


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Vertical Axis Wind Machine:Savonius rotor

Darrieus rotor


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Savonius and Darrieus rotors

Wind machine sites


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Site requirement

Pros and cons of wind machines


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Wind power capacity

Wind power capacity


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Wind Farm

Challenges

Large area required

Create ecological disruption

May create aesthetic objections

Localized sites

Seasonal


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Web Sites of Interest

www.windpower.org

www.eere.energy.gov

www.awea.org

www.nrel.gov

Questions?1. A wind turbine of the two-blade propeller type is designed to

have its maximum power coefficient value at a tip-speedratio, TSR = 6, when the wind velocity is 25 mph. If theblade diameter is 100 ft, what is the recommended speed orrotation?

2. Wind turbine units are rated at 2 MW in a rated wind speed of13 m/s. The stage efficiencies are Cp = 0.32, gb = 0.94, g= 0.96. What is the necessary swept area? If the rotor is atwo-blade propeller (horizontal axis), what is the rotor

diameter?

3. Lets assume that there are about 1500 land-based sites forwind machines with 3 MW capacity each, having wind

speeds of 20 mph. What portion of the demand forelectricity consumption of 400 TWh could be supplied?

l11 - energy sources - wind

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