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

How a wind turbine rotates 2

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 C P (=P MAX /P 0 ) becomes 16/27 = (Lanchester-Betz limit)

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:

How wind turbines distributed (Making wind farms) d as the diameter of the wind turbine  Space in the horizontal direction  from 2 d to 4 d  Space in the vertical direction  from 8 d to 12 d