Not every wind turbine is suitable for every site.
A criterion for suitability for example could be the given climate conditions at the site: an experienced developer knows at which range of temperatures, wind conditions, etc. the considered wind turbine type is able to operate without restrictions.
Another criterion e.g. is the Sound Power Level of a wind turbine type (being associated with its noise emission): there are significant differences between turbine types and manufacturers. A wind farm developer like NewEn has all relevant information about market proven wind turbines and is able to take all of these factors into account while planning the wind farm layout.
How does a wind turbine work?
The principle of a wind turbine is rather simple.
The energy of the wind causes the propeller-like blades of the wind turbines to rotate. The rotor is connected to the main shaft inside the nacelle which connects to a gearbox that in turn converts the slow motion into a fast motion. The fast motion is required by the generator, which uses magnetic fields to convert the rotational energy into electrical energy. A transformer converts the electrical energy to the appropriate voltage for distribution via the existing grid.
There are many different wind turbine designs, with plenty of scope for innovation and technological development. The dominant wind turbine design is an up-wind, three bladed, pitch controlled and variable speed machine.
Components of a wind turbine:
Wind turbines have just one, two or three blades. Nowadays most turbines have three. These are made from glass fibre reinforced plastic and lightwood. The colour of the blades can differ between various site locations. Often blades are marked with red stripes which is to improve flight security and depends on the surrounding area, maximum tip height and the appropriate law. Most manufacturers have a well developed lightning protection with special receptors mounted on the blade. Some manufacturers offer heating of the blades to avoid icing.
The rotor hub connects the blades to the nacelle and transfers the power to the main shaft.
Some years ago the connection of blades and hub had been rigid. Today the blades can be turned a) to secure the highest efficiency by rotating the blades to a position where the maximum energy of the wind can be harvested and b) to stop the operation of the turbine, which would be necessary for maintenance or when excessive winds might inflict danger on the wind turbine or in case of a failure. The system responsible to turn the blade into the right position is called ‘pitch system’. The pitch system (hydraulic or electric) is located in the hub.
The nacelle houses the turbine including every mechanical and electrical component.
The yaw mechanism turns the nacelle with the hub and the blades so that they face directly into the wind. It is situated between the nacelle and the tower. The control of the yaw system is influenced by the wind direction, measured on top of the nacelle.
The main shaft is made of steel and passes the motion of the rotor to the gearbox. A bearing mounted on the bed plate of the nacelle is holding the main shaft in its position.
There are different types of gearboxes on the market (spur gear, planetary gear or a combination of both). Their task is to convert the slow motion of the main shaft into the fast rotation required for the generator. Some manufacturers do not use a gearbox but install a generator working with low rotation (‘direct drive’). These generators have to be significantly larger but on the other hand the omission of a gearbox often results in reduced maintenance work.
Generally a wind turbine has two brakes: one are the blades, reducing the speed can be accomplished by turning only one blade – or in general all blades “out of the wind” so that rotation is reduced or stopped alltogether. The other is a mechanical disc brake mostly mounted on the fast shaft between the gearbox and the generator. For wind turbine designs without any gearbox the manufacturers have found some other solutions for their brake system.
For service and maintenance work the rotor can be locked manually.
Generally there are two different types of wind generators: synchronious and asynchronius (induction generator).
Nowadays most wind turbine manufacturers use doubly-fed asynchronius generators (allowing variable rotational speed). Turbine designs without gearboxes use synchronous generators (annular generators).
All variable speed turbines need to convert their electrical energy coming from the generator to a certain frequency to ensure compliance with the grid code.
The quality of the electricity produced by the generator is variable – depending on the rational speed of the shafts (therefore originally influenced by the wind). To fulfill the local grid code requirements the frequency converter transfers the electricity from alternating current (AC) to direct current (DC) and again to AC but with a certain frequency (e.g. 50 Hz in Europe, 60 Hz in Northamerica and Korea).
The wind turbine generates low voltage energy which has to be transferred to middle voltage energy before being fed into any grid. Large wind farms require a substation to transform the middle voltage energy to high voltage energy to feed into the prevailing high voltage transmission line.
The SCADA system (Supervisory Control And Data Acquisition) allows the telemonitoring of any turbine from the service centre of the manufacturer, provided there is a fast internet connection.
All data collected at the wind turbine (e.g. temperature, wind direction, wind strenght, oil pressure) and any reaction of the turbine (e.g. pitch angle, yaw angle, heatening or cooling of components) are visible to the manufacturer online who controls each and every turbine throughout the entire year on a 24/7 basis. The owner and operator of the turbine very often can have access to the main data as well.
Many of the instruments/sensors (e.g. anemometer, wind vane, shadow detector if any) are visibly mounted outside on the nacelle, some are connected inside (e.g. vibration sensors).
There are many tower types on the market such as pure steel towers, concrete towers, lattice towers and hybrid towers (hybrid tower: concrete and steel for the upper part), cylindric or conical or a mixture from both.
In general the height of a tower is decisive for the wind energy turbines efficiency. The higher the tower, the stronger the wind at hub height and the less turbulent – and as a result: the higher the annual electrical output. Naturally higher towers are more expensive, therefore each wind farm requires its own individual solution.
NewEn has the experience to find the best solution for your wind farm