Wind Turbine Power Control
The intent of a wind turbine is to harness available energy from the wind and convert it into usable electricity in as inexpensive a method as possible. For that reason, wind turbines are usually designed to provide maximum energy output when the wind is blowing at up to a rate of 15 meters per second. Higher wind speeds are unusual, which would yield the turbines ineffective, so the rate of 15 meters per second is used to provide consistent and reliable energy.
When the wind blows at higher speeds, the excess energy can actually damage the wind turbine. Power controls are in place that are used to intentionally waste some of the energy in order to prevent damage to the turbine. There are two types of power controls that are used on wind turbines: pitch controlled turbines and stall controlled turbines.
Pitch Controlled Wind Turbines
The first type of power control that is used on wind turbines is the pitch controlled turbine. The turbine’s electronic controls monitor the energy output of the turbine. When the energy output gets too high, it activates the blade pitch mechanism. This mechanism turns the blades so that they are out of the wind. When the wind slows down, the blades turn back to their regular position in the wind. This setup requires that the blades are able to turn around the longitudinal axis. Under normal circumstances, the blades will turn just a fraction of a degree at a time while the rotor is also turning.
A pitched controlled wind turbine must be carefully designed so that the blades turn just the precise amount necessary. The electronic controls of the turbine will turn the blades several degrees as the wind changes so that the blades stay at the correct angle to provide maximum energy output. The blades are usually turned using hydraulics.
Passive Stall Controlled Wind Turbines
The blades of a stall controlled wind turbine are attached to the hub at a fixed angle. The profile of the blade is designed so that when the wind speed gets too high, turbulence is created on the side of the blade that is not facing the wind. This stalls the blade and prevents it from turning. In a stall controlled wind turbine, the rotor blades are slightly twisted along the longitudinal axis. This detail causes the blades to stall gradually when the wind increases, rather than stopping suddenly.
One advantage of stall controlled wind turbines is that the power control doesn’t require any computerised controls or any moving parts in the rotor. The majority of wind turbines that are installed worldwide – about 2/3 – are stall controlled.
Active Stall Controlled Wind Turbines
Some larger wind turbines use an active stall control method. These machines have pitchable blades, like a pitch controlled turbine. However, when the wind speed gets too high, these machines rotate their blades in the opposite direction. This forces the blades to stall, so that the extra wind energy is wasted.
An active stall gives the user more control over the power output than a passive stall.
If you are interested in using a wind turbine to provide an alternative, inexpensive source of electricity, contact Windpower Technology. At Windpower Technology, we are the experts on providing renewable electricity through small scale wind turbines and solar PV technology. Give us a call today, and we will help you through the development and installation of your small scale wind turbine.