Why do wind turbines have 3 blades?

If you are the curious type, it may have occurred to you over the years to wonder why most wind turbines have 3 blades. It seems a bit of an odd number – why not 2 or 4, or even just 1? The answer is actually quite interesting – so I will talk you through the various reasons as to why wind turbines have all converged towards the 3 blade model.

A question of balance

The one blade model suffers from the issue of balance. Unlike other types of blade configuration, the 1 blade design can only be balanced by weighting the system, as there is no way of making the blades symmetrical. Weighting the blade is fiddly and adds to the cost, so whilst a one blade turbine might be the best option with respect to some of the variables involved, the fares badly in this respect, and as such is seldom seen commercially.

Aerodynamics – one blade disturbing the air for the next

As the blade on the turbine moves, the air behind it becomes disturbed and turbulent. This reduces the effectiveness of the next blade that is passing through it. This would tend to suggest that the fewer the number of blades the better, because there will be more time for the air to settle before the next blade passes through.

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So if you combine these 2 factors, 2 blades would certainly seem to make sense – maximum distance between blades, but also balance that you don’t get with one blade. Adding a third blade however, will add even more stability

Length of the blade

One other factor that affects the blades is the speed at which they rotate Naturally, the longer the blades, the faster the tips are going to be travelling. With less blades, they rotate quicker – and as the tips approach the speed of sound, there is a big loss in efficiency. That means it is in the interest of the designer to ensure that the blades aren’t going to spin too fast – one way to do this whilst still achieving excellent efficiency is to increase the number of blades.

So as you can see, with larger turbines there is going to be a trade off between less blades on one hand and more on the other.

More blades are expensive

The more blades you add to the system, the more the cost of producing it. This may seem obvious, but every pound counts when you are trying to produce energy from a turbine, and going to a 4 turbine system is going to cost more to produce.

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By weighing all these factors up, there is an obvious compromise to be reached. The 3 blade turbine combines the various factors into an acceptable middle ground that is efficient, and cost effective to produce. So when you next see a turbine with three blades, you will know why…

Think we missed something? Do you have a different opinion?

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