Why do wind turbines always have three blades?

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If you have seen a wind farm, you have noticed that wind turbines have 3 blades. Why not 1 blade, 2 blades, 4 blades or 5 blades ? Because the aim is when the power is produced not to capture more wind. The aim is capturing wind with greatest efficiency. And as a result it is found that 3 blades is the most efficient and less troublesome way.

 Wind turbine with one blade

It is not common but when you see a wind turbine with one blade, you shouldn't surprise. It looks like a little different from the other common wind turbines even the working principle is same. Due to one blade, it is cheaper from the others. On the other hand the aesthetic of the one bladed turbine is a little worse. Whole wind energy sector compromise about 3 blade wind turbines due to aesthetic. If we look more detail, the efficiency of the one bladed turbine is higher, but the loads are also higher due to unbalance rotor. What's more it tends to spin faster. That's why it is much more noisy.

2 bladed offshore wind turbine

As it seen the previous figure, sometimes two bladed wind turbines can also be seen. The same phenomena about aesthetic is valid for two bladed wind turbine also. But this has higher efficiency than the one bladed and 3 bladed wind turbines. When we compare with 3 bladed wind turbines, the only advantage  is one blade is less, that's why it is cheaper. It is cheaper from the rotor side but on the other hand  because of higher loads the maintenance costs and the life of turbine must be considered also. 

3 bladed wind turbine 

Due to aesthetic, efficient loads 3 bladed wind turbines are much more common. When it is compared with the other types of wind turbines, powerful enough and it is less noisy because of tending to spin slower. Noise issue is also must be considered when a wind turbine constructed. Because of these reasons 3 bladed wind turbines are accepted in wind energy sector.

Wind turbine with 5 blade

When the number of the blades are increasing, normally cost of turbine is also increasing. That's why the turbines which have more than 3 blades seen rarely. If we look from the technical side, when we have more than 3 blades, we must make them lighter. When they are lighter, they will tend to spin faster and they will be broken. That's why generally it is not good idea to use more than 3 blades.