Most power-producing wind turbines do change direction. Small, residential turbines simply use a tail to face them into the wind.
Large, commercial wind farm turbines use wind direction, wind speed, a computer, and motors to optimize their orientation. But, there is more going on than just facing the wind.
- Wind Direction.
- Blade Angle.
- Blade Rotation.
- Rotation Speed.
A Wind Turbine is essentially a generator like we use at home. Instead of a gasoline engine to spin the generator head, the turbine harnesses wind energy to turn the generator.
A wind turbine can produce a lot of electricity under the right circumstances.
Facing The Wind
Usually, wind turbines like to face the wind. They can rotate 360 degrees to make the best use of whatever wind is available. A wind turbine receives the most wind energy if it is facing directly into the wind.
Small, domestic wind turbines use a tail to keep the blades facing the wind. Large, wind farm turbines, use sophisticated electronics to optimize their orientation to the wind. This movement is known as YAW.
Mechanical Yaw Adjustment
Simple, domestic wind turbines use a tail to adjust their yaw. Under normal circumstances, the tail will keep the blades of the unit facing directly into the wind.
This maximizes rotation speed and power output. Under certain circumstances, the tail will furl. When winds exceed the safe operating speed of a wind turbine, the tail will employ a furling movement to decrease wind speed.
The tail will move to a yaw angle of about 45º to slow the rotation of the blades. When the wind speed drops to a safe speed, the tail will return to its regular orientation.
Electronic Yaw Systems
Large wind turbines used in wind farms do not use tails to control yaw. Wind speed sensors, wind direction sensors, and air temperature sensors all feed data to a computer.
This computer determines the optimum yaw orientation to maximize power output while avoiding power spikes from high-speed winds.
Motors within the nacelle of the turbine adjust the yaw angle.
This is one reason some wind turbines may not be facing directly into the wind when observed.
Reasons for Yaw adjustment
- Manage orientation to wind direction.
- Maximize power generation.
- Avoid generator damage from excessive wind speed.
- Minimize power spikes from wind gusts.
Blade Angle
The blade pitch, or angle, of a wind turbine blade, can affect two things: The torque at the axis of the blade assembly and the rotational speed.
By varying the blade angle, engineers can maximize power output for a specific wind speed range. In the case of home turbines, this angle is set.
In the case of commercial wind turbines, the blade angle can be adjusted to optimize the power output at various wind speeds, or even stop the turbine in the event of extreme weather.
Home Turbine Blade Angle
The blade pitch of a typical wind turbine is between 30º and 35º. On a home wind turbine, this value is fixed and can not be changed.
It is set to optimize power output for the power generator over a specific range of wind speeds. In the case of fixed blade angles, furling and electronic breaking are used to limit blade rotation speed in extreme weather.
Commercial Turbine Blade Angle
The blades of commercial wind turbines are adjustable. Hydraulic or electronic drive systems within the hub of the blade assembly can vary blade pitch to take maximum advantage of low wind speeds or to retard rotation in the event of high wind speeds.
In the past, braking systems similar to domestic units were ineffective at protecting the large turbines.
Today, most commercial turbines can move the blades to a dead flat setting that will stop, or nearly stop, rotation in extreme weather.
Advantages Of Variable Blade Angle
- Optimize power output at various wind speeds.
- Can retard rotation speed to avoid power spikes.
- Increased safety during high wind events.
- More effective at protecting system in extreme weather.
Blade Direction of Rotation
The modern wind turbine rotates in a clockwise direction when viewed from an upwind, or frontal, perspective. It has been accepted as a standard.
There are a few rather arbitrary reasons for this, and until recently it did not seem to matter.
However, in the past few years, research has suggested that the rotational direction of wind turbines may have a significant impact on performance under certain circumstances.
It is all fairly complex, but really interesting. In the future, we may see turbines going in both directions! A good link is included below.
Rotational Speed of Wind Turbines.
While the speed of the wind does impact every wind turbine, the rotation of the blades in relation to wind speed is not the same.
If you have ever seen a commercial wind turbine turning in a 20 mph wind, and then seen it again in a 30 mph wind, you have noticed the rotational speed does not change much. In those same circumstances, a domestic wind turbine will appear to spin much faster. Why?
Factors That Affect Turbine Rotation Speed
- Blade Mass.
- Generator Design.
- Blade Pitch.
- Dynamic Braking.
Domestic Wind Turbine Rotation Speed.
The rotation of a small, domestic wind turbine is tied directly to wind speed. These units are simply a set of blades mounted to a generator.
As the wind blows harder, the blades spin faster. Faster speed equals more power. A charge controller will step higher power down to accommodate the battery bank.
In many cases, the only adjustment to rotation speed is from the furling feature. In some cases, a domestic turbine may employ dynamic braking that slows the blade rotation.
This feature usually kicks in when the battery bank is full.
Commercial Wind Turbine Rotation Speed
The rotational speed of a commercial wind turbine is a function of mass, speed reduction gearing, and electronic braking. A commercial wind turbine blade can exceed 100 feet in length and weigh over 10,000 pounds.
In addition to the sheer magnitude of the turbine, speed reduction gears within the nacelle hold the speed down by converting it to torque.
The increase in torque can drive a larger, more efficient generator housed within the nacelle. Finally, in extreme wind conditions, dynamic braking and blade pitch control can slow rotation.
All of these features go into making a commercial wind tower very efficient while protecting itself from high winds.
Wind Turbines
Wind Turbines are very sophisticated devices. They can rotate to face the wind, slow themselves down, and adjust themselves to take advantage of every gust that comes their way.
What you see when you pass a wind farm is more than just some windmills. It is a spectacular array of technology on display.
Sources
Wind Energy Basics 1
Wind Energy Basics 2
Clockwise vs Anti-Clockwise: Blade Rotation Direction.
Blade Pitch
