Wind power generate AC or DC ? Why ?

Wind Turbines generate AC Current. Thats due to the oscillation in the rotational speed of the shaft ( which depends on the wind profile) at a certain and time and location 

It depends on the type of the generator it can either DC or AC.

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normally wind turbine generate Ac current.

wind power is generated as AC because it can Stored easily in capacitors as DC and whenever Demand is their it is Converted into AC and Transmitted. Hope This one is correct?

Wind turbine design is the process of defining the form and specifications of a wind turbine to extract energy from the wind. A wind turbine installation consists of the necessary systems needed to capture the wind's energy, point the turbine into the wind, convert mechanical rotation into electrical power, and other systems to start, stop, and control the turbine

The speed at which a wind turbine rotates must be controlled for efficient power generation and to keep the turbine components within designed speed and torque limits. The centrifugal force on the spinning blades increases as the square of the rotation speed, which makes this structure sensitive to overspeed. Because the power of the wind increases as the cube of the wind speed, turbines have to be built to survive much higher wind loads (such as gusts of wind) than those from which they can practically generate power. Wind turbines have ways of reducing torque in high winds.

A wind turbine is designed to produce power over a range of wind speeds. All wind turbines are designed for a maximum wind speed, called the survival speed, above which they will be damaged. The survival speed of commercial wind turbines is in the range of m/s ( km/h, MPH) to m/s ( km/h, MPH). The most common survival speed is m/s ( km/h, MPH).

If the rated wind speed is exceeded the power has to be limited. There are various ways to achieve this.

A control system involves three basic elements: sensors to measure process variables, actuators to manipulate energy capture and component loading, and control algorithms to coordinate the actuators based on information gathered by the sensors.

There are many different kinds of generators that could be used in a wind turbine, right now I am going to just group them in three different types.

Induction Generator

An induction generator is a type of electrical generator that is mechanically and electrically similar to an induction motor. Induction generators produce electrical power when their shaft is rotated faster than the synchronous frequency of the equivalent induction motor. Induction generators are often used in wind turbines and some micro hydro installations. Induction generators are mechanically and electrically simpler than other generator types. They are also more rugged, requiring no brushes or commutator.

Induction generators are not self-exciting, meaning they require an external supply to produce a rotating magnetic flux, the power required for this is called reactive current. The external supply can be supplied from the electrical grid or from the generator itself, once it starts producing power or can you can use a capacitor bank to supply it. The rotating magnetic flux from the stator induces currents in the rotor, which also produces a magnetic field. If the rotor turns slower than the rate of the rotating flux, the machine acts like an induction motor. If the rotor is turned faster, it acts like a generator, producing power at the synchronous frequency. In the United States it would behz.

The common down side of using an induction generator in a wind turbine is gearing. Typically you need an induction motors to run+ RPM to meet the synchronous so a gearing is almost always needed.

Permanent Magnet Alternators

Permanent magnets alternators (PMA) have one set of electromagnets and one set of permanent magnets. Typically the permanent magnets will be mounted on the rotor with the electromagnets on the stator. Permanent magnet motor and generator technology has advance greatly in the past few years with the creation of rare earth magnets (neodymium, samarium-cobalt, and alnico). Generally the coils will be wired in a standard three phase wye or delta.

Permanent magnet alternators are can be very efficient, in the range of%-%, typically around% though. As a generator they do not require a controller as a typical three phase motor would need. It is easy to rectify the power from them and charge a battery bank or use with a grid tie.

It is easy to build a permanent magnet alternator, even for beginners. This is a common choice for home builders. I will have some great information on this site a little later that will take you through the design and building process. You just need to understand a little science and have some sort of mechanical competency.

Note: Car alternators are not PMA but actually have a field coil instead of permanent magnets, and are typically very inefficient around%. They typically need to be spun+RPM to get any real power out of them, but with a belt or gear arrangement can still do a decent job.

Brushed DC Motor

Brushed DC Motors are commonly used for home built wind turbines. They are backwards from a permanent magnet generator. On a brushed motor, the electromagnets spin on the rotor with the power coming out of what is known as a commutator. This does cause a rectifying effecting outputting lumpy DC, but this is not an efficient way to “rectify” the power from the windings, it is used because it’s the only way to get the power out of the rotor. A good brushed motor can reach a good efficiency, but are typically at most%.

There are many great advantages to using a brushed motor. One of the biggest reasons is because typically you can find one not requiring any gearing and still get a battery charging voltage in light wind. They are also quite easy to find, they can be purchased from eBay, surplus supply stores, industrial supply stores, and can find them on different things that might get thrown away or given away (like a treadmill).

The efficiency of a wind turbine is a maximum at its design wind velocity, and efficiency decreases with the fluctuations in wind. The lowest velocity at which the turbine develops its full power is known as rated wind velocity. Below some minimum wind velocity, no useful power output can be produced from wind turbine. There are limits on both the minimum and maximum wind velocity for the efficient operation of wind turbines.

Ac And Dc Due to variable wind speed

Generally its AC. However it is not impossible to make the output into DC thus it can be either AC or DC. Depending on the construction of the turbine the output will vary. However mostly its AC since the turbine is used to feed into the grid and generally the Grid transmission is in AC.