How Fast Do Wind Turbines Spin?

Wind turbines can spin at speeds of up to 190 mph with a rotational speed of around 20 RPM.

That’s pretty impressive, considering the blades on these turbines can reach 107 meters long.

This article discusses wind turbines’ mechanics, how they spin, and what affects their speed.

How Do Wind Turbines Spin?

Drag and force power in wind turbines
The effect of lift and drag forces on wind turbine’s blades (Creative Commons CC0)

Wind turbine blades are designed with a concave shape on one side and a convex shape on the other.

This helps to create more drag in front of the blade than behind it.

This difference in pressure causes rotation when wind hits them – much like an airplane wing will generate lift when air passes over it.

What Affects The Speed of a Wind Turbine?

1. Wind Speed

Chart relation of wind speed to rpm.
Chart relation of wind speed to rpm by Esmar Budi

Wind speed is one of the most significant factors determining how fast a wind turbine will spin.

Higher winds create more lift and drag on the blades, which causes them to rotate faster.

2. Blade Length

Relationship-between-blade-tip-speed-and-wind-speed-for-wind-turbines-at-5-wind
Relationship between blade tip speed and wind speed for wind turbines by Cris Hein

Longer blades create more drag and generate more power than shorter blades. This is because there is more surface area for the wind to hit, which causes more lift and drag.

However, longer blades are also heavier, requiring stronger wind to rotate them at high speed.

Engineers must strike a balance between these two factors when designing wind turbines.

To make their turbines as efficient as possible, they design the blades to be very thin so that they can spin faster in lower winds.

3. Tower Height

Relation between height and wind speed
Relation between height and wind speed by Ahmed Samir Badawi

The height of a wind turbine affects how fast it spins. At higher altitudes, the wind is stronger, with less turbulence.

This means that the turbine can spin faster since it doesn’t have to fight as much wind resistance.

Wind Turbine Rotation Speed

Wind turbines’ RPM (Rotations Per Minute) speed is the number of complete rotations the blade makes in one minute.

The average wind turbine spins at a rate of 15-25 RPM.

However, this number varies depending on the type of turbine and the wind conditions.

Some turbines have a maximum RPM of over 30, while others only reach 13 or 14 RPM.

It’s important to note that rotation speed isn’t always constant throughout the day. There are times when it will slow down, for example, when there is no or little wind.

Tip Speed

Tip speed is the velocity of the blade’s highest point. The higher the velocity, the faster the tip makes a full rotation around its axis, so it’s simply another way to measure RPM.

Tip speed is important because if it’s too low, most of the wind will pass through the gap between the blades, creating little to no lift force to help the rotor spin.

Conversely, if the tip speed is too high, the blades will blur, acting as a solid wall to the wind, reducing the turbine’s efficiency.

Further, the tip speed determines how much noise a wind turbine makes. The higher the tip speed, the more noise the turbine will produce.

Wind turbines are designed to have a tip speed of under 190 mph. Anything over that can cause damage to the turbine and create a lot of noise.

Here’s how to calculate the tip speed:

S = 2 x 𝝅 x r x RPM

Where

  • S = Tip Speed
  • 𝝅 = 3.14
  • r = Blade Length
  • RPM = Rotations per minute

How Does RPM Affect Efficiency?

A typical power versus speed characteristics of a wind turbine.
Power versus speed characteristics of a wind turbine by Rajveer Mittal

It’s not always better for RPM to be higher.

At higher RPMs, wind turbines produce more noise and vibration. This is harmful to people and animals in the turbine’s vicinity and can put a lot of stress on the turbine.

Higher RPM doesn’t necessarily mean that the turbine is producing more energy.

It’s often better to have a turbine that spins slower but has longer blades to catch more wind than having a turbine that spins too fast.

A turbine that spins too fast for its size will not be as efficient because it will put a greater load on the gearbox, reducing the turbine’s lifespan.

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