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 Solar chimney 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 Tip vane 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 CP (=PMAX/P0) becomes 16/27 = 0.593 (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 2d to 4d Space in the vertical direction  from 8d to 12d