Question
• Ministry of Science and Technology,Renewable Energy Directorate- Iraq

# Why is usually three of blades on a wind turbine instead of say 5 or more?

Can anyone give me a complete explanation about using 3 blades on a wind turbine instead of another number especially in the utility-scale wind turbine types?

Leonard Mwankemwa
Sokoine University of Agriculture (SUA)
Ali K. Resen If the number of the blades increases the efficiency of rotation will decrease due to some reasons including vane acts as a wind breaker,

Mohamed Benbouzid
Université de Bretagne Occidentale
Dear Ali,
Regarding your question, I am attaching a document (even in french) in which it is shown the number ob blades impact on the power coefficient (Cp - left figure)) and the Yaw Moment (right figure) of a wind or marine turbine. When analyzing these curves, it came obvious that a three-blade turbine is the best choice in terms of Cp (even reduced but with a larger TSR range) and Yaw Moment (less oscillations of the turbine pile).
Regards,
Mohamed
3 Recommendations

## Top contributors to discussions in this field

Mohamed Benbouzid
Université de Bretagne Occidentale
Dear Ali,
Regarding your question, I am attaching a document (even in french) in which it is shown the number ob blades impact on the power coefficient (Cp - left figure)) and the Yaw Moment (right figure) of a wind or marine turbine. When analyzing these curves, it came obvious that a three-blade turbine is the best choice in terms of Cp (even reduced but with a larger TSR range) and Yaw Moment (less oscillations of the turbine pile).
Regards,
Mohamed
3 Recommendations
University of Tabriz
1 Recommendation
Tamer Qaimari
RWTH Aachen University
Hallo Ali,
stability problems will be main problem when we have 1 blade so it is not an option. two blades Turbine has gyroscopic precession problem.
more Blade number = more torque = Slower speed due to drag force
since the main Purpose of Turbine is generating Electricity at high speed where torques is not much of importance the ideal number becomes 3 which is dynamic stable with optimum Drag force
1 Recommendation
Ali K. Resen
Ministry of Science and Technology,Renewable Energy Directorate- Iraq
Thank you Mohamed Benbouzid for your answer, it is clear from figures that one blade causes many problems structurally and dynamically, so it is not very feasible on a large scale.
Ali K. Resen
Ministry of Science and Technology,Renewable Energy Directorate- Iraq
Thanks Claudio Pedrazzi , in addition to the cost and structure problems, some articles says :
A three-bladed wind turbine has infinite principle axes in the plane swept by the blades, which makes it the most efficient turbine design without having any dynamic issues. This is why pretty much all large wind turbines these days are three bladed.
Ali K. Resen
Ministry of Science and Technology,Renewable Energy Directorate- Iraq
Thank you Tamer Qai for your opinion.
I agree with you , more torque means slower speed , but the wind turbines need to operate at high speeds and don't need much torque for generating electricity.
regards
stability problems will be main problem when we have one blade
1 Recommendation
Halefom Kidane
Hawassa University
it is fact if the number of blades increase the generated power will also increase .But most of the wind parks uses three bladed turbine due to the their aerodynamic balances in these turbines safe because the angle between each blade is 120 degree .So main reason to select three balded is their balancing system
1 Recommendation
Leonard Mwankemwa
Sokoine University of Agriculture (SUA)
Ali K. Resen If the number of the blades increases the efficiency of rotation will decrease due to some reasons including vane acts as a wind breaker,

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