KEY POINTS:
Why are we asking this now?
Because Contact Energy is to start building a giant wind farm south of Port Waikato in 2010. With 218 turbines, standing 150m high, Hauauru ma raki - as it will be known - could be among the biggest in the world.
The project will cost about $2 billion and have the potential to produce up to 650MW, enough to power about 250,000 homes.
The turbines would cover an area of 320sq km, 35sq km bigger than Great Barrier Island.
What are they for?
A wind turbine is a machine that converts the kinetic energy in wind into mechanical energy. That energy is then converted to electricity that can be supplied to homes.
Wind causes the turbine's blades to spin. The rotating effect is transmitted through a turbine shaft into a gearbox which steps up the rotations per minute so that a generator is able to spin at enough speed to generate electricity. They start generating when wind speeds reach about 14 km/h.
There are seven wind farms in New Zealand - Brooklyn in Wellington, Hau Nui in the Wairarapa, Gebbies Pass and Southbridge in Canterbury, and Tararua, Te Apiti and Te Rere Hau in the Manawatu.
Are wind turbines noisy?
They usually produce a swishing sound created by the revolving rotor blades.
Some older turbines can produce a steady hum or whine caused by mechanical components or unusual wind currents hitting parts of the turbine.
However, in 1998 Standards NZ produced a standard for the assessment and measurement of sound from wind turbines. It was developed as an aid for resource consents and to provide guidance on the limits of acceptability for sound received at residential and noise-sensitive locations. Developers must comply with this standard.
Do they kill birds?
Many people are afraid that wind turbines kill a large number of birds and opponents of wind power will often use the argument to stop developments.
There is no definite number of how many birds have been killed by wind turbines but it has been recorded that it is in the millions worldwide annually.
Many energy companies try to avoid flight paths of birds when constructing a wind farm and may consult with Forest and Bird and ecological experts. There have been no recorded incidents of bird mortality at Brooklyn.
What is the history behind wind turbines?
Wind machines were used for grinding grain in Persia as early as 200BC and in the Roman Empire by 250AD.
By the 14th century, Dutch windmills were used to drain areas of the Rhine River delta.
The first wind turbine for electricity production was built in Cleveland, Ohio by Charles F Brush in 1888.
