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How Fast Do Wind Turbines Spin? (Not As Slow As They Look)

How Fast Do Wind Turbines Spin? (Not As Slow As They Look)

When I was reading about the topic of wind energy, I started to wonder how fast wind turbines really spin. So, I continued my research to find out the speeds that wind turbine blades actually move while creating electricity. 

How fast do wind turbines spin? Wind turbines begin turning when wind speeds are around 7 to 9 miles per hour and braking systems begin kicking in when wind speed is around 50-55 mph to prevent damage. At higher wind speeds the tips of the blades can get up to around 180 mph!

The speed of the wind turbine depends on how fast the wind is blowing. Most wind turbines are turning at about 10 to 20 rpm. When wind speeds are around 12-15 mph the tip of the blades are turning at about 120 mph.

From a distance, the blades of a wind turbine might look like they rotate relatively slowly, but this statement couldn’t be further from the truth. Most people would be surprised to find out that wind turbines are actually not as slow as they look. 

Related: Just Three Blades? Why Most Wind Turbines Use Three Blades

Wind Turbine Speeds in Rotations Per Minute (RPM) 

The speed of a wind turbine can be measured in a few different ways, depending on what you would like to find out about the machine. One of these units of measurement is called rotations per minute (RPM). The results of this calculation will tell you how many rotations occur per minute.

Rotation occurs when the rotor blades complete one full circle about the axis. You can find out what the RPM of a wind turbine is in one of two ways. First, you can use a timer and manually count how many full rotations happen within that time frame.

To make this easier, you can tie something to the end of one of the blades as a marker to help you keep track. Alternatively, you can use a tachometer tool to find the most accurate result for rotations per minute. 

Average Wind Turbine Speeds

The average, modern-day wind turbine’s blades spin at a speed of about 15-20 rotations per minute. The generator within the turbine, on the other hand, moves at a speed of approximately 1,800 rpm in order to convert the wind’s energy into electricity. 

Wind turbine blades should not spin too slow or too fast but should be somewhere in the middle for the best results. If the blades are spinning too rapidly, they will create turbulence between them and will end up blocking the wind from entering through the gaps.

On the other hand, if the blades are not moving fast enough, they will not catch the wind’s energy in time before it slips through the gaps and bypasses them.

A Wind Turbine’s Tip Speed Ratio (TSR)

Another measurement that is performed on wind turbines is called the Tip Speed Ratio (TSR). This will help you find out how long it takes the blades to travel one circumference in a rotation time that is specified in seconds. It is important to know this number because it will help you monitor the efficiency of your wind turbine.

To find the tip speed, you will first have to measure the length of one blade and find the speed. Speed is calculated by dividing the circumference by time in seconds, with the circumference being 2(pi)r. The result of this calculation is then divided by the wind speed, which can be determined by the use of a speed meter tool.

Once you know the tip speed ratio for your wind turbine, it is easy to find out if this number is an optimum ratio for your turbine. This will mean that it is balanced enough to help you get the most power from the wind as possible. 

The Optimum Tip Speed Ratio For a Wind Turbine

An optimum tip speed ratio will help your turbine create more energy from the wind and operate as efficiently as possible. The ideal tip speed ratio will depend on the number of blades on each turbine. The formula for a perfect tip speed ratio is 4(pi) divided by the number of blades.

This equation can be applied to any turbine and will be the most accurate formula to find this number. As a quick reference, a turbine with only 2 blades should have a tip speed ratio of about 6. On the other hand, a 3-blade turbine should have a TSR or close to 4 or a 5.

This number gradually decreases when more blades are added to the turbine, so a 4-blade turbine should have a tip speed ratio of approximately 3, and a ratio of 2 can be expected for a turbine that has up to 6 blades. 

The Factors That Influence a Wind Turbine’s Speed

There are various factors that can influence a wind turbine’s speed including the speed of the wind, air density, and the size and quantity of the blades.

The internal design of wind turbines stops them from reacting to certain speeds of wind. In general, the speed of the wind will be reflected in the wind turbine’s blades. Faster wind speeds create more of a push causing the blades to spin more rapidly. The brake function is used within the nacelle to stop rotations if wind speeds are too fast and could cause damage to the machine’s hardware. 

There is a certain threshold of motion in which the wind turbines will operate. These limits are known as the cut-in speed and the cut-out speed. The cut-in speed is the minimum wind speed to where the turbine can gain power from it and take its energy.

Anything below this limit will not get a reaction from the turbine’s blades at all. In other words, the wind must have enough power to be able to push the blades into rotation or else they will stand idle until speeds increase.

The average minimum speed, or cut-in speed, that is necessary for most wind turbines to begin movement is about 10 miles per hour. For machines with larger blades, this number can increase by a few miles per hour since they require more force to be exerted by the wind to trigger the rotors to spin. 

The cut-out speed is over the maximum amount of wind speed the turbine blades can handle. When the turbine reaches this limit, all functions must be stopped immediately. Basically, the blades will only spin if the wind speed is between these two numbers that are usually set when the turbine is initially built and programmed.

For the average wind turbine, the maximum possible speed is just over 130 miles per hour. However, some larger and more durable turbines can get up to speeds of 180 miles per hour.

Different levels of air density can affect the speed of the wind turbine’s rotor blades. Air density is a combination of the location’s altitude, pressure, and the temperature of the air. If any of these additional factors are pushing the air onto the rotor with more force than usual. it will help the turbine create more power than it would in another circumstance. 

Turbines that have larger blades will generally catch more of the wind’s kinetic energy. This is able to happen because a blade that stretches out further is able to push the wind with more power and move it through its internal system.

These types of turbines, however, need to have additional space between them because the reach is so big. Multiple machines that are too close can disturb each other and affect productivity. Additionally, turbines with larger blades will only react to faster wind and will not be moved if the levels of pressure are too low. 

There are many different ways to answer the question of how fast wind turbines spin, depending on what you are trying to find out or improve upon. Ultimately, the blades on a wind turbine have the ability to spin at rapid speeds event though they might look slow from a distance. 

Related Questions 

What are the Components of a Wind Turbine That Make the Blades Spin?

The speed of the wind is first determined by the wind turbine, which is usually done with something called an anemometer. The anemometer is a small piece on top of the nacelle that rotates and sends a message to the inside of the machine.

The frame inside the nacelle will then move the rotor toward the direction of the wind so the blades can take in its kinetic energy and pass it through the body of the turbine. From there, the blades will react to the speeds of the wind and rotate about their axis accordingly. 

Are Wind Turbine Rotor Blades Supposed to Move Fast?

Although the blades on a wind turbine have the potential to get up to extremely fast speeds and have the capability to stop themselves if the weather conditions are too dangerous, it is still better for the blades to move on the lower end of the spectrum.

Spinning at an extremely high speed can create more of a risk for damage to the parts as well as additional wear before the turbine has lived out its entire life span. Lower speeds are also preferable because if the blades are moving too fast, the turbulence created between them can block the turbine from receiving the wind’s kinetic energy. 

Learn More

If you’re serious about learning more about wind energy, I recommend the Wind Energy Handbook on Amazon. This book is great for both students and professionals, and it holds invaluable information on the subject of wind power.