Have you ever seen a wind farm or a wind turbine? A wind turbine is rather like a giant fan. When the wind sets it spinning, it generates electricity. Wind turbines can range in size from small ones installed on large yachts and small buildings, to giant ones like those shown in Figures 1 and 2.

A wind farm is a set of wind turbines that are linked together to supply electricity to a local community or to an electricity grid for a larger population. Many are located along coastlines where the winds are strong. The Woolnorth wind farm in Tasmania, shown in Figures 1 and 2, is an example of this.

 

Figure 1: A coastal view of the 140 MW Woolnorth Wind Farm, located on the far north-west coast of Tasmania where the Great Southern Ocean meets Bass Strait. Up until April 2008, this was the biggest wind farm operating in the southern hemisphere. This title now belongs to the Lake Bonney Wind Farm in South Australia, at 239.5 MW. PHOTO CREDIT: Roaring 40s

Figure 2: A close-up view of some of the wind turbines at Wool north Wind Farm. The van at the base of one of the towers, and the cattle in the background, give some idea of their size. PHOTO CREDIT: Roaring 40s

How do wind turbines work?

Wind turbines transform the kinetic energy of the wind into electrical energy.

Figure 3 shows the key energy transformations that take place.

Figure 3: The energy transformations that take place in a wind turbine

The main steps are:

STEP 1: Moving air pushes against the blades of the turbine, which are tilted to the direction of the wind. This makes the blades spin. In the process, some of the kinetic energy of the moving air is transformed into the mechanical energy of the spinning blades. (The wind still has some kinetic energy as it flows away from the turbine.)

STEP 2: The shafts and the gears inside the gear box transfer the mechanical energy of the turbine to the generator. (The gears make the drive shaft to the generator spin faster than the shaft connected to the blade hub.)

STEP 3: The generator transforms mechanical energy into electrical energy.

Figure 4 shows a close-up view of a wind turbine. Figure 5 shows what wind turbines might look like on the inside.

Figure 4: A close-up view of a wind turbine at the Woolnorth wind farm. PHOTO CREDIT: Roaring 40s.

Figure 5: A wind turbine – an inside view
Source: http://www.alliantenergykids.com/wcm/groups/wcm_internet/@int/@aekids/documents/image/022691.jpg
Accessed: 4 January, 2011

What is the best place to locate a wind farm?

Wind turbines must, of course, be located where there are steady strong winds - though not so strong they would damage the turbines.

They work at their greatest possible energy efficiency, however, when they operate in 'smooth' air - that is, when the air particles are moving in the same direction and not whirling around and moving in different directions.

Ideal sites for wind turbines therefore are:

• Away from obstructions such as forests, towers and rocky outcrops. (These would cause the air to whirl around.)
• At the highest point possible.

The best place is on top of a smooth hilltop, where the wind can concentrate and increase in speed.

What determines how much power is generated by a wind turbine?

Wind turbines do not produce electricity all the time. Although the wind might be available for as much as 70% of the time, it is often not strong enough to operate the wind turbine at full capacity. The combination of absence of wind and inadequate wind strength means that even in a good location the wind turbine, over the course of a year, will generate only about 30% of the amount it could generate in a constant strong wind.

The amount of electrical power produced by a wind turbine doesn't only depend on the speed of the wind, and how smoothly it flows, however. It also depends on the way the turbine is built:

• The number of blades
• The length of the blades
• The shape of the blades
• The weight of the blades
• The pitch (angle) of the blades to the wind
• The height of the tower
• The gears used
• The type of generator used
• The computer system that controls the operation of the turbine and its power output (where this is used)

What is the energy efficiency of wind turbines?

A good site might have a 35% capacity factor. This means that the turbines will produce 35% of their capacity on average over a year.

Apart from problems with the wind itself, some of the kinetic energy of the wind is 'wasted', due to the fact some is transformed into heat energy (the gears and shafts get hot) and sound energy ( the blades, gears and shafts make some noise as they spin). This is summarised in Figure 6.

Figure 6: A Sankey diagram showing how some of the kinetic energy of the wind is transformed into forms of energy that are not useful.

What are the advantages of wind turbines?

The main advantages of wind turbines, once they are built*, are:

1. They are a renewable energy resource – we always have wind!
2. They do not emit greenhouse gases or any other pollution.
3. They are more energy efficient than most power stations that burn fossil fuels.
4. They are less costly to run than many other energy resources.
5. They can be established in remote areas where other energy resources are not practical, even in places like Antarctica and on ocean-going yachts.

*Greenhouse gases and other pollutants are produced during the manufacture, transport and installation of wind turbines, but once they have operated for a year or so, they will have compensated for this. Overall, wind turbines help reduce the amount of greenhouse gases emitted into the atmosphere.

Figure 7 shows one of the wind turbines that were built by an Australian company in Antarctica. The headquarters of this company are in Darwin.

Figure 7: A wind-diesel energy resource that was built by Dr Alan Langworthy and his company, Powercorp Pty. Ltd., at the Mawson base in Antarctica. Alan also has built wind turbines at the Murdoch and Scott bases. PHOTO CREDIT: Powercorp Pty. Ltd

What are the disadvantages of wind turbines?

Some of the disadvantages of wind turbines are:

• The electrical power delivered varies because wind speed and direction vary. Sometimes the wind speed is too low to even start rotation. Therefore they can only be used to provide some of the electrical power people need.
• They can be damaged by very strong winds and also corroded by salt in the air when near the sea.
• It can be costly to connect them to the electricity grid, due to the distances involved.
• Some people think they spoil the landscape.
• They need to have flashing lights on the top to warn the pilots of any aircraft that fly overhead of their presence. People who live close by sometimes complain the flashing lights disturb their sleep.
• In many countries, most wind turbines are constructed off-shore, usually because people do not want them across the land. This is a much more expensive location, because the turbines are more costly to install and to maintain, because of problems such as corrosion of metal parts by sea water and damage from the constant movement of waves and sand. This means the electricity they generate is more expensive than that generated by coal-fired power stations.
• There may be some impact on local bird populations.

The noise issue

Some people believe the sound produced by wind turbines is annoying or even harmful.

However, tests conducted by Danish sound engineers on many wind turbines in Denmark have shown that the loudness of sound heard in any location depends on wind direction and speed. The engineers reported that they often could not detect any sound above normal natural levels in areas near wind turbines. Even when they could, the loudness of the sound was not of a level that would harm people's hearing.

They also found that no infrasound is produced by wind turbines. Infrasound is low frequency sound that cannot be detected by the human ear. It is thought to cause a number of health problems.

What say do local communities have?

Many local communities, or the majority of members of local communities, are very happy to have a wind farm installed near them. Usually farming communities, they benefit from the jobs such developments bring into their area.

Moreover, wind turbines are often installed on farms and provide the farmers with extra income. Cattle and sheep still graze peacefully under them (as shown in Figure 2).

However, local communities can object to the installation of a proposed wind farms if they wish. The arguments they may raise include:

• The potential damage to local sacred Aboriginal sites
• The effect on the appearance of the landscape and possible impact on any local tourist industry
• Noise
• The possible impact on the local environment, and on local populations of birds and other animals

Figure 8: Protest signs at a farm located near a wind farm in Victoria. PHOTO CREDIT: The Age