Wind Power

Windmills are used in a number of different applications for generating electrical power to pumping water.

The power output of a windmill may be estimated using the following equation:

where
P = power [kW]
A = swept area of sails [m2]
v = velocity of wind [ms-1]
DesignAdvantagesDisadvantages
HAWT
  • Most commercial machines use this design because it is well understood.
  • High efficiency: about 40% efficient,not too far from the theoretical limit of59%.
  • Relatively low material costs becauseblades are few (2 or 3 usually) and thin.
  • Complexity is increased because the blades must be turned into the wind by a “yaw” mechanism.
  • Alternator must be atop a tall tower, thus is hard to access for maintenance.
Drag based VAWT (Savonius)
  • Easy to build·
  • Few moving parts, no “yaw” mechanism needed·
  • Slow speed of rotation means parts don’t wear out as fast.
  • Alternator is near ground level.
  • Lower efficiency. Estimates range from 15% to 24% efficient as compared to 40% for other designs.
  • More material needed to build, because the blades are totally covered.
Lift based VAWT (Darrius)
  • Few moving parts, no “yaw”mechanism needed.
  • High efficiency. Nearly 40% efficient.
  • Alternator is near ground level.
  • Blades travel at near sonic speeds (500 to600 miles per hour) and thus are under alot of stress.
  • Design is less well understood.

See also: Energy Return on Energy Invested, Horizontal Axis Wind Turbine, Renewable Energy, Sail Wing, Vertical Axis Wind Turbine.

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Subjects: Mechanical Engineering


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