Wind Power and its Science

As one of the powerful energy sources

The first windmill / wind turbine

During 500–900 AD, windmills were built in Persia for pumping water and grinding grains.

In 1888, Charles F. Brush used a windmill to generate electricity in Cleveland, Ohio, as is called a wind turbine nowadays.

The advantages

Small environmental load Little pollution

Equal to the efficiency of thermal power with a best circumstance Twice as much as that of solar cells

More secure than other energy sources

Usage of wind energy

For charging batteries Work saving

Pumping water to storing water when wind is available, etc.

Hybrid generating system Hybridized with other generators

The energy payback time (EPT)

With a 2000-kW class wind turbine,7m/s of year-average wind velocity

It can create 7 million-kWh electricity a year

The power consumed by 1,400 households

The average EPT is 3 to 4 months.

Measurement of wind velocity Cup anemometer

World standard

Doppler LiDAR (Light Detection And Ranging) Using Doppler effect Able to measure at 200-m height

Types of windmills / wind turbines

Horizontal Axis Wind Turbine (HAWT) More common and commercialized Dutch windmill Propeller type, etc.

Vertical Axis Wind Turbine (VAWT) Independent of directions of wind Darrieus Savonius Giromill, etc.

Other wind turbines 1

Magnus wind turbine From the effect discovered by Heinrich

Gustav Magnus Using long cylinders instead of blades

Solar chimney wind turbine Air heated by sun going up in the

chimney The wind turbine installed in the chimney

Other wind turbines 2 Diffuser

With 10% increment of wind velocity, 30% increment of the power generated

Tip vane Removing vortex at the

tip of the blade

How a wind turbine rotates 1

Low pressure zone

High pressure zone

Fluid resistance

Lifting force

Wind velocity

Blade

How a wind turbine rotates 2

Savonius-type wind turbine

Puddle type

The wind for rotation

The wind against rotation

Axis

Savonius type

Axis

The wind for rotation

The wind against rotation

The net wind for rotation

Types of wind turbines and the power

A small number of blades The power becomes larger, but the

torque is smaller.

A large number of blades The power becomes smaller, but the

torque is larger.

The number of blades and usage of wind turbines/windmills

One or two blades are capable of generating the best power.However, they get noise most.

Three-blade wind turbines are the best balanced.

Multiple-blade windmills are used for pumping water due to larger torques.

Theoretical efficiency of windturbine The maximum power

of windmill received from wind

The entire power from wind covered by the windmill

The power coefficient CP (=PMAX/P0) becomes 16/27 = 0.593 (Lanchester-Betz limit)

31max 2

1

27

16SvP

310 2

1SvP

Practical efficiency of windturbine

Fluid mechanical loss About 50%

Mechanic loss About 4%

Electrical loss About 6%

The practical energy efficiency is 40%.

Size of a windturbine and its power

The power of wind

where , A, v are the air density, the area of windmill, and wind velocity, respectively.

Therefore, the power is proportional to the square of the wind velocity:

322

2

1

2

1

2

1AvvAvmvP

2vP

How wind turbines distributed(Making wind farms)

d as the diameter of the wind turbine

Space in the horizontal direction from 2d to 4d

Space in the vertical direction from 8d to 12d

d

2d – 4d

8d – 12d

Wind