Wind Electric

A Brief History of Wind

After the 1930s many isolated rural areas used small wind turbines for direct current electrical power. The extension of the Western Australian grid since the 1940s has greatly reduced their use. Isolated farms have caused an upsurge of interest in small-scale wind powered electricity generation in recent times. They are sometimes used in conjunction with small diesel generators and photovoltaic cells in remote off grid areas.

How Do Wind Turbines Work?

Wind energy conversion systems ('wind turbines') are designed to convert the energy of wind movement (kinetic energy) into mechanical power, that is the movement of a machine. In wind turbine generators, this mechanical energy is converted into electricity and in windmills this energy is used to do work, such as pumping water, mill grains or drive machinery. Electricity generated can be either stored in batteries, or used directly. There are three basic physical laws governing the amount of energy available from the wind.

The first law states that the power generated by the turbine is proportional to the wind speed cubed. For example if the wind speed doubles, the power available increases by a factor of eight; if the wind speed triples then twenty seven times more power is available! Conversely, there is very little power in the wind at low speed. This law means that accurate and detailed local wind speed data is necessary to determine the likely energy yield from a given site, and generators should be chosen for that particular site. Average wind speed information alone is often of limited value.

The second law states that the power available is directly proportional to the swept area of the blades. That is the power is proportional to the square of the blade length. For example, doubling the blade length will increase the power by four times, and tripling the blade length will increase the power by nine times.

The third law states that there is a maximum theoretical efficiency of wind generators of 59%. In practice, wind turbines are less efficient than this, due to system losses. The best wind generators have efficiencies of about 53%. Practical wind turbines are designed to work between certain wind speeds. The lower speed, called the 'cut in speed' is generally 3 - 4 ms-1, as there is too little energy below this speed to overcome system losses. The 'cut out speed' is determined by the ability of the particular machine to withstand high wind. The 'rated speed' is the wind speed at which the particular machine achieves its maximum rated output. Above this speed, it may have mechanisms that maintain the output at a constant value with increasing wind speed (see Figure 1).

Figure 1 Power Output from a Wind Turbine as a function of Wind Speed.

Figure 1 shows an ideal power curve for a small wind turbine with a furling mechanism. Vc is the cut-in speed at which the turbine starts to produce power, Vr is the rated speed at which the turbine reaches it's rated power and Vf is the furling speed, which is the wind speed at which the machine shuts down to avoid damage. Pr is the rated output of the turbine. This curve would be typical of a horizontal-axis tow or three bladed machine. The curve is ideal as the machine follows the peak power available from the wind until it reaches the generator capacity and then regulates to maintain a steady output until shut down.

Components of a Wind Turbine

A wind turbine usually comprises the following parts (see Figure 2):

Rotor: The blades of the rotor are designed to spin in the wind, driving the turbine generator. Sometimes gearing is used to increase the frequency for electricity generation.

Generator: This generates the electricity when there is sufficient wind to rotate the blades. There are now many designs of generator, including some with new powerful permanent magnets. Electricity is transferred to the next stage (either for storage, exporting to the grid or for direct use) using cabling.

Directional system: Horizontal axis machines require a mechanism to swing them into line with the wind. Small machines usually have a tail assembly for furling. Large machines usually have a 'servo mechanism' that orients them into the direction of maximum output.

Protection system: Modern wind turbines are usually equipped with mechanisms to prevent damage in excessively high winds. Large machines may use active methods involving aerodynamic and mechanical brakes to shut down generation at high wind speeds. Smaller systems may use passive methods such as furling or changing the blades' pitch so that they present a smaller surface to the wind and thereby reduce the speed of rotation.

Tower: The tower raises the turbines assembly well above the turbulent air currents close to the ground and captures higher wind speeds, as described earlier in this fact file. Tower design is particularly critical, as it must be as tall as economically possible, robust, enable access to the turbine for maintenance, and yet not add unnecessarily to the cost of the system. A particularly important aspect of tower design is elimination of resonance between the frequency range of rotating blades and the resonant frequency of the tower.

Figure 2 Major sub-components of a large-scale wind generator
(courtesy of CREST and the Renewable Energy Policy Project – Wind Turbine Development : Location of Wind Manufacturing (PDF)).

Wind Capacity Worldwide and in Australia

Globally there are many countries that have invested heavily in wind technologies. Figure 3 below is a pie chart of distribution via the worlds continents.

Figure 3 Percentage of world installed capacity by continent in 2007 (derived from the World Wind Energy Association (WWEA )world statistics 2007 publication (PDF)).

Even though Australia is a small player on the world stage the domestic wind installed capacity is making inroads to the energy mix. Figure 4 shows the cumulative MW installed capacity from the year 2000 to 2006.

Figure 4 Installed capacity in Australia from 2000 to 2006.(courtesy of the Australian Wind Energy Association’s (Auswind) Trade Winds 2004-05 publication (PDF) and the International Energy Agency).

Large Scale Wind Turbines in Australia

Wind turbines are rated according to the power output they produce, and range from a few kW up to a few MW. Table 1 below shows a list of the existing wind projects in Australia of installed capacity greater than 10 kW.

PROJECT & LOCATION	OWNER/ DEVELOPER	CONNECT.	YEAR	MAKE, TURBINE	No.	TOTAL SIZE
Breamlea VIC	Barwon Water	Grid	1987	Westwind 60kW	1	0.06
Flinders Island 1 TAS	Hydro Tasmania	Wind Diesel	1988	na 55kW	1	0.055
Salmon Beach* WA (Decommissioned)	SECWA, now Verve	Wind Diesel	1988	Westwind 60kW	6	0.36
Cooper Pedy SA	na	Wind Diesel	1991	Nordex 150kW	1	0.15
Coconut Island (decommissioned) QLD	Ergon Energy	Wind Diesel	1992	na 10kW	1	0.01
Ten Mile Lagoon WA	Western Power	Wind Diesel	1992	Vestas 225kW	9	2.025
Aurora (Brunswick) VIC	Citipower	Grid	1993	na 10kW	1	0.01
Flinders Island 2 TAS	Hydro Tasmania	Wind Diesel	1996	na 25kW	1	0.025
Armadale WA	na	Grid	1997	Westwind 30kW	1	0.03
Kooragang Island, Newcastle NSW	Energy Australia	Grid	1997	Vestas 600kW	1	0.6
Thursday Island QLD	Ergon Energy	Wind Diesel	1997	Vestas 225kW	2	0.45
Crookwell NSW details	Eraring Energy	Grid	1998	Vestas 600kW	8	4.8
Huxley Hill, King Island TAS	Hydro Tasmania	Wind Diesel	1998	Nordex 250kW	3	0.75
Denham WA	Verve	Wind Diesel	1999	Enercon 230kW	3	0.69
Epenarra NT	na	Wind Diesel	1999	Lagerway 80kW	1	0.08
Blayney NSW	Eraring Energy	Grid	2000	Vestas 660kW	15	9.9
Murdoch WA	RISE	Research	2000	Westwind 20kW	1	0.02
Windy Hill QLD	Stanwell	Grid	2000	Enercon 600kW	20	12
Albany WA	Verve	Grid	2001	Enercon 1.8MW	12	21.6
Codrington VIC	Pacific Hydro	Wind Diesel	2001	Bonus 1.3MW	14	18.2
Hampton NSW	Wind Corporation Australia	Grid	2001	Vestas 660kW	2	1.32
Exmouth Advanced WA	Verve	Research	2002	Westwind 20kW	3	0.06
Toora VIC details	Stanwell	Grid	2002	Vestas 1.75MW	12	21
Woolnorth Stage 1 TAS	Hydro Tasmania	Grid	2002	Vestas 1.75MW	6	10.5
9 Mile Beach WA	Verve	Wind Diesel	2003	Enercon 600kW	6	3.6
Challicum Hills VIC	Pacific Hydro	Grid	2003	NEG Micon 1.5MW	35	52.5
Huxley Hill stage 3 TAS	Hydro Tasmania	Wind Diesel	2003	Vestas 850kW	2	1.7
Mawson Base** AAT details	Australian Antartic Division	Wind Diesel	2003	Enercon 300kW	2	0.6
Starfish Hill SA details	Tarong Energy	Grid	2003	NEG Micon 1.5MW	23	34.5
Bluff Point (Woolnorth Stage 2) TAS	Hydro Tasmania	Grid	2004	Vestas 1.75MW	31	54.25
Canunda SA	International Power/ Wind Prospect	Grid	2004	Vestas 2MW	23	46
Hopetoun WA	Verve	Wind Diesel	2004	Enercon 600kW	1	0.6
Lake Bonney Stage 1 SA	Babcock & Brown National Power	Grid	2004	Vestas 1.75MW	46	80.5
Rottnest Island WA	Rottnest Island Board	Wind Diesel	2004	Enercon 600kW	1	0.6
Bremer Bay WA	Verve	Wind Diesel	2005	Enercon 600kW	1	0.6
Cathedral Rocks SA	Hydro Tasmania & Acciona Energy	Grid	2005	Vestas 2MW	33	66
Cocos (Keeling) Island WA	PowerCorp/Diesel & Wind Systems	Wind Diesel	2005	Westwind 20kW	4	0.08
Mount Millar (Yabmana)	Tarong Energy	Grid	2005	Enercon 2MW	35	70
Walkaway WA	B&B/National Power Partners/Carbon Solutions	Grid	2005	Vestas V82 1.65MW	54	89.1
Wattle Point SA	Southern Hydro & Wind Farm Developments	Grid	2005	Vestas 1.65MW	55	90.75
Wonthaggi VIC details	Wind Power Pty Ltd	Grid	2005	REpower 2MW	6	12
Emu Downs	Stanwell Corporation/Griffin Energy	Grid	2006	Vestas 1.65MW	48	79.2
Yambuk VIC	Pacific Hydro	Grid	2006	NEG Micon 1.5MW	20	30
					Subtotal	817MW

Table 1 Installed capacity in Australia.(courtesy of Auswea).

For a similar table of proposed installations in Australia, visit this Auswea link.

For a some interesting facts about wind installations in Australia, visit this Auswea link.

Small Scale Wind Turbines

Wind turbines that have a rated capacity of less than 10kW are usually classified as small-scale turbines. These turbines can also be connected to the grid, but more commonly are used to generate electricity as part of a Remote Area Power Supply (RAPS) or Stand-alone Power Supply (SPS) system in regions where the grid is unavailable. Figure 5 shows four 20 kW Westwind turbines used on Home Island in the Cocos (Keeling) Islands.

Figure 5 This small wind turbine generator is part of a hybrid RAPS system
(Image courtesy of Westwind Turbines).

Windmills/Wind Pumps

Windmills have been used in Australia to pump water from underground bores for nearly a century, and are a common sight in rural Australia. They are designed to operate at lower wind speeds than wind turbines for electricity generation. Windmills 'store' the energy they produce in water tanks so that water is available for feeding livestock, or irrigation in times where there is no wind. These windmill water pumping designs have also been used to provide electricity for rural electrification by using a battery system and low voltage systems. Today the more modern and efficient triple bladed rotor is commonly used in such stand-alone power systems.

Figure 6 A traditional style multiblded wind pump, known as a windmill.
(Image © 2005 Oklahoma Farm Bureau).

Managing Variability in Wind Turbine Systems

The greatest challenge to the economic use of wind power is its variability. There are very few areas on the Earth where wind is fairly constant throughout the day and throughout the year. Energy storage, or a backup system, is therefore required for windless or extremely windy periods and to supply energy even when the wind is blowing in a suitable range.

For small systems (up to a few kW) storage systems similar to those used for photovoltaic systems are used. This generally comprises a bank of deep-cycle lead-acid batteries. In hybrid generation systems, wind turbine generators are often coupled with a traditional diesel generator and an array of photovoltaic cells.

For larger systems, the problem of variability is more complex. One possibility is to build an interconnected grid with wind turbines at different locations, thereby reducing the probability of windless conditions. Proposals have also been made to couple wind generators to pumped hydroelectric storage. Suitable sites for economic storage are required for this option. The present strategy is to not consider storage in large grid connected systems, where wind generators are used primarily to replace conventional fuels. Some studies have shown that large grids can absorb about 30% wind penetration without effecting the management of the grid system, although Western Power Corporation's Denham wind project aimed at 70% penetration. If none of these options are economically viable, then large systems must be seen to be fuel savers for conventional systems, with full backup required. However, depending on the wind regime, the backup system may be less capital intensive than baseload systems. For example, gas turbines, which are cheaper to install than a coal-fired system, may be viable in some circumstances, or low load diesel gen sets. New technologies are playing a part in this area. Supercapacitors are being installed by some major wind turbine manufacturers to improve some of the electrical quality issues that are caused by some wind technologies. Flywheels are also a technology that has been applied to this task.

As with other forms of solar energy, another form of storage is to convert the energy directly into its end use. For example, it is normal to use water storage tanks together with wind powered water pumps. In special cases, the energy may be stored directly in the form of heat for water or space heating, as purified water (with reverse osmosis machines), or even in the form of ice for refrigeration.

Australian Researchers

Australia is active in wind power research with major activity occurring at the University of Newcastle, the University of Technology Sydney, and the Research Institute for Sustainable Energy (RISE). CSIRO also have a Wind Energy Research Unit.

The Industry in Australia

Australia has a flourishing wind power industry, which is involved in research and development on small wind turbines as well as sales and service. Examples of the main firms involved are Westwind and Powercorp. Most large turbines are imported from overseas. The major electricity utilities are also involved in demonstrating and testing the applications of wind power. Those with active research and development wind power programs include Verve, Great Southern Energy, Energy Australia, Pacific Power and Hydro Tasmania.

The Future

Although the generation of electricity from wind turbines has been economically marginal for many years, the future looks quite optimistic following the development of large-scale systems in both Europe and the United States. Improved subsystem technologies, the move towards mass production and installation experience are all serving to reduce costs significantly and wind turbines have become competitive with conventional-fueled systems in areas with a good wind resource.

For small-scale power generation in remote areas, the main competitor until recently was liquid-fueled systems. Many remote area power supplies (RAPS) combining wind and photovoltaics with diesel backup are now being installed. The outlook for large grid-connected wind farms is promising, with several utilities operating wind monitoring stations.