For the House

HOW DOES IT WORK?

Wind turbines use the wind to turn a propeller to produce an alternating voltage and current. These are rectified to provide DC current which is usually used to charge a battery bank. This stored energy can then be used to supplement general energy use.

HOW MUCH CAN I SAVE?

The amount of power the system is able to generate will depend of the size of the system and the amount of wind in the area. Household size systems range from a 300 watts to 5kw with the average being about 1kw. The table below shows the daily AC upload that can be met by a 1kw wind generator at various wind speeds.

 

WIND POWER
Ave Wind Speed Metres/Second	Daily AC Load that can be supplied(Wh)
3	690
4	2.142
5	3,060
6	5,585
7	7,650
8	9,180
9	10,863
10	12,470

 

HOW MUCH DOES IT COST?

 

As with most things it depends on the quality of the product, the style of system, location of the install and the quality of service provided by the supplier. We recommend talking to a professional who can match a system to your individual requirements.

GOVERNMENT INCENTIVES

Solar Credits are provided in the form of environmental certificates called small-scale technology certificates (STCs) for eligible small-scale solar photovoltaic (PV), wind and hydro electricity systems.

While it is possible for owners of renewable energy systems to create and sell the STCs themselves, in practice installers of these systems usually offer a discount on the price of an installation, or a cash payment, in return for the right to create the STCs.

When you are assessing your quote be sure to consider the STC’s as part of the quote.

MORE INFORMATION

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.

A growing amount of renewable electricity is being harnessed from the wind. Australia has an abundant supply of wind resources, which, if utilised adequately, can save significant greenhouse gas emissions. This fact sheet provides an overview of installing and using wind systems.

INSTALLING DOMESTIC WIND SYSTEMS

Domestic wind generators (also called turbines) are usually used in stand alone power systems and are designed to charge a battery bank. Domestic wind generators are usually sized in the range of 300W up to 5kW but in some instances they could include a 10kW or 20kW turbine.

New developments in wind turbines include noiseless vertical axis turbines.

Conventional wind turbines have the turbine axis in the horizontal plane, but a number of innovative designs are being developed employing a vertical axis turbine, and some with more aerodynamic features or shrouded blades to improve the performance of small horizontal axis machines.

These changes are aimed at reducing noise and providing a better output under turbulent wind conditions likely to be experienced around buildings. Test results are promising and some commercial models are making it to the installation stage. The remainder of this fact sheet relates to the commercial horizontal axis wind generation.

The main body of the wind generator comprises a set of blades, the alternator and the tail section. The power of the wind makes the blades turn. The blades are connected to the rotor inside the alternator which turns and generates electrical power. The tail ensures that the wind generator is facing directly into the wind.

Wind speed increases as the height above the ground increases.

Output of a wind generator is dependent on the amount of wind but can also vary from one manufacturer to another.

To help appreciate what you can expect from a wind generator the following table shows the daily AC load in watt hours (Wh) that can be met by a 1000 Watt wind generator at various average wind speeds.

Inverter and battery efficiency have been taken into account in accordance with design guidelines. A household electricity usage of 5,000kWh per year equates to about 13.5kWh per day.

Care should be taken in determining the wind resource of your site.

As a rule of thumb, a wind generator should be installed no closer to an obstacle than at least ten times its height, and on the down wind side. The preferred distance is twenty times the height.

Wind speed increases as the height above the ground increases, so the wind generator should be installed on the highest tower that is practical and cost effective for your site. The typical tower used in domestic wind generator systems is between 10-20m tall.

SITING AND INSTALLATION

Wind generators need ‘clean’ wind to operate. Clean wind is where the wind is constant from the one direction and is not being made turbulent by near-by obstacles. The clean wind is required to overcome the starting torque (that is the starting resistance) of the wind generator.

Wind can be affected by terrain like hills, trees and nearby buildings or structures. Some areas of Australia receive seasonal wind and may only receive winds in winter while in coastal regions on the east and west coasts the prevailing wind will be summer sea breezes.

Most manufacturers will provide figures on the ‘cut-in’ wind speed. This is the speed of the wind (generally measured in metres/second) at which the starting torque is overcome and the wind generator begins to turn and generate power. In areas with frequent light winds, a low cut-in speed is an important feature for maximum output. Manufacturers provide a rated output of a wind generator at a specified wind speed. Not all manufacturers rate their units at the same wind speed.

In Australia there is very little wind monitoring undertaken, so the system designer will have very limited wind data to use to design the system. Designers will use their own experience, knowledge and relevant information obtained from the manufacturer when determining the anticipated output of the wind generator system.

To overcome the power loss in the cables, the wind generator needs to be located as close as possible to the battery bank. If the preferred site is distant from the house, the batteries and inverter could be located near the wind generator and the power transmitted as 240V AC to minimise cable losses. Alternatively the generation voltage can be higher and then transformed down to battery voltage if the batteries are installed near the house. Higher voltage transmission means lower losses.

Wind generators can produce some running noise in high winds. The noise can come from the blades, gear-box, brush gear or wind whistling past the tower, pole or guy wires. The noise may not be loud but may be noticeable to you or close neighbours. The background noise of the wind itself usually covers the sound of the blades. Always ensure that there are no objections to the low level noise produced.

TURBINE CONTROLS

As the wind speed increases the wind generator will spin faster. If wind speed continues to increase the generator may ultimately be destroyed. All wind generators therefore have a wind ‘cut out’ speed at which the unit will employ some form of overspeed control to either stop the unit generating power or govern the rotational speed to produce constant power.

The two most common forms of overspeed control are mechanical braking and feathering.

In mechanical braking, a brake, similar to those found in many cars, is applied as a result of the centrifugal forces developed when the unit approaches the cut out speed. If the unit is operating in an area where the average speed is close to the cut out speed, braking might happen frequently and the brakes will wear out rapidly.

Feathering can occur in two ways: either by rotating the individual blades to reduce their angle into the wind, thereby reducing rotor speed; or turning the whole unit out of the wind.

Wind generators are always producing power when turning. If the batteries are fully charged the excess power is redirected into a dummy load, usually an electrical element. The dummy load can get very hot and should be positioned where it will not be touched accidentally.

TOWER DESIGN AND INSTALLATION

Wind turbines require regular maintenance and the tower needs to be designed to allow access for servicing mechanical components, such as bearings.

The typical tower is designed so that it can be lowered and raised by tilting the tower with a gin pole and winch.

If a tilt tower and gin pole is used there must be sufficient area around the wind tower for it to be lowered. If it is 20m tall you will need at least 20m area for lowering the tower. If a vehicle is used to raise and lower the tower it also needs room to manoeuvre.

ENERGY USE

Tilt towers are guyed, so although the tower might only be constructed from 100mm pipe, the guying of the tower will have a footprint of 20 x 20m for a 19.5m tower. The guy wire tensions will need to be checked regularly.

The tower and the guy wires will usually require concrete footings. These footings must be designed in accordance with the wind loadings for the particular site.

Wind generators and the accompanying system, being mounted on top of metal towers, are very susceptible to lightning strikes. Lightning arresters should be installed in the system to protect electronic components from the effects of lightning strikes.

Components of a commercial farm wind turbine:

Blades: 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.

Rotor hub: 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.

Nacelle: The nacelle houses the turbine including every mechanical and electrical component.

Yaw system: 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.

Main shaft: 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.

Gearbox: 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.

Brake: 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.

Generator: 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).

Frequency converter: 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).

Transformer: 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.

SCADA system: 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).

Tower: 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.