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Wednesday, July 28, 2010

Enabling Wind Farms

submitted to the New Zealand government in 2010 in response to a request for submissions on her energy policy

Enabling Wind Farm

Because of the nature of our (New
Zealand's) existing electrical generating infrastructure, the addition of wind turbines is more effective in New Zealand than for most other countries of the world. However, the construction of wind farms is being blocked at every turn by concerned citizens. Some of their concerns are pure Nimbiism and dislike of change but some of their concern may be justified. The government needs to honestly and thoroughly investigate such concerns associated with existing wind farms and then prepare and disseminate a paper on their findings in clear, easily understood language. If some of the concerns are genuine, the government must then help with the necessary research to solve these problems. Such an approach will ease the introduction of wind farms which are so essential for the future well being of New Zealand.

Much is made by many commentators of the need for more research into ways of producing renewable energy. There is of course truth in their assertion. However, it draws attention away from the fact that one of the best forms of renewable energy, namely wind turbines, is already well up the technological learning curve. Wind energy is already very competitive, cost wise, with other energy sources. As you look to the future with the steady increase in the cost of fossil fuel and our Kyoto
commitment, wind generated electricity will rapidly become the most viable option. As with many of the problems which face us today such as population increase, water degradation, green house gases and so forth, the problems are not ones of technology but of vested interests. The technological solutions are obvious.

Wind farms, because of their intermittent generating characteristics need huge storage batteries to balance their output. New Zealand is rich in such batteries. They are called hydro-electric dams. Every KWh produced by wind leaves water in the dams to be instantly used when the wind decreases. Here in New Zealand, because of the availability of already developed hydro power, wind turbines are more economically viable than for most other countries in the world. This is especially so since the generation capacity of our hydro generators is well above the sustainable energy generation capacity (determined by the amount of water flowing into the dam). This means that a dam can be drawn down, producing energy at a far greater rate than it's sustainable rate when necessary, and allowed to accumulate energy (water) when the wind is blowing strongly. This balances a similar, though not identical characteristic of wind turbines.

A one MW wind turbine is not expected to generate one megawatt continually throughout the year. Sites are rated for the availability of wind (capacity factor) and at a 30% site, over the year or years, you would expect to generate on average 0.3MW of power. However, this means that when the wind is at the optimum speed, a full MW is being generated for every nominal (nameplate) MW of generating equipment. Under these conditions, water (energy) can be left to accumulate behind the hydro dams. I repeat, a MW of wind generating capacity in New Zealand is worth more than the same capacity in almost any other country of the world.

Despite the obvious benefits of wind farms, at every turn there are fanatical objectors. The objections fall into a number of categories. These are

*Aesthetic. While some people, such as myself, find wind turbines things of beauty both for their elegant form and for what they represent, others do not.

*Shadow Flicker. This is the effect when the sun is directly behind a wind turbine from the point of view of an observer.

*Glint. Glint refers to the reflection of sunlight off the blades of a turbine and may occur when the sun is to the side or behind the observer.

*Noise. This includes audible noise transmitted through the air and low frequency sub-audible noise, primarily transmitted through the ground.

Lets have a look at each of these and then see what the government could do to ease the introduction of wind turbines.

The solution

There is not a lot that can be done about this problem. In Europe, where electricity is expensive where the cost of electricity is subject to fossil fuel price fluctuations , where there are many potentially dangerous nuclear power plants and where air pollution is far worse than in New Zealand, many people see wind farms, at the very least, as the lesser of a number of evils and at best, things of beauty. We are somewhat spoiled in New Zealand.
(See appendix 2)

Shadow Flicker

Shadow flicker occurs when you, the wind turbine and the sun are perfectly lined up. Unless you are very close to the wind turbine, a situation that is avoided by wind farms, the change in the intensity of light is very small and occurs for at most a few minutes on a few days per year. What the government can do in this regard is to publish as part of a paper on wind turbines, a well thought out explanation with suitable diagrams explaining the absurdity of worrying about shadow flicker. (see Appendix 1)


Glint can occur as different parts of the wind turbine reflect the sun to the observer. It is virtually eliminated by using matte paints on the turbine blades and by using light absorbing colors. Having the wind turbines a reasonable distance away from the observer also reduces any significant glint. Here the government must check out any reports of glint, determine if they actually exist, measure their intensity and duration and publish the results. If glint is indeed discovered from some wind turbines, a small research effort could be mounted to find an appropriate paint which will solve the problem.


The air born noise of a modern wind turbine which are constructed with acoustic isolation of the internal machinery from the nacelle and acoustic isolation of the generator from the blades along with the correct shaping of the blades makes it virtually impossible to separate air born turbine noise from the sound of wind through the trees at anything beyond a kilometer. In most instances you must be well within a km to hear a wind turbine. The effects of low frequency sound which propagate through the ground must be taken more seriously.

If an individual turbine does indeed produce low frequency sound and if it transmits the sound to the ground, such vibrations can propagate. Depending on the geology of the area, these vibrations can be propagated in unexpected ways. It is within the realm of possibility (just) that these vibrations could come up under a house, for instance, to the annoyance of the occupants. So what must the government do to address this problem.

All reported cases of low frequency sound from existing turbines should be investigated. This would involve
a) scanning the frequencies, if any, which are being transmitted from a turbine to the adjacent ground,
b)making measurements at the site of the complainant to see if any of these frequencies are showing up at the location in question,
c) stopping one or more turbines to see if that stops the vibrations (the same frequencies could be from a different source) and
d) applying dampers to any offending turbines and going back to "a".


What is needed is for the government to sponsor a small research project that examines any reported cases of annoyance from wind turbines and determines if they are justified. If any of these complaints prove to be justified, the government should lend a hand to find solutions.

(Appendix 1) Shadow flicker
Shadow flicker is a red herring. If you are any distance at all from the turbine, shadow flicker is virtually nonexistent. I will use the example of my house here in Waipara which is 5000m from the Mt Cass ridge to the East. The diameter swept out by a 3mw wind turbine is typically 90m. 90m at a range of 5000m makes an angle of 1.03 degrees of arc. From the observers point of view, looking at the horizon, the sun comes up at a different place each day. The amount it moves each day is 1/4 degree. Therefore, each wind turbine you can see from your house will have the sun behind it for 4 days as the sun 'travels' south and 4 days as it travels North. A total of 8 days per visible wind turbine.

The sun rises at 15minutes of arc(1/4 degree) per minute of time. If there was any flicker from a wind turbine at that range, it would last for just over 4 minutes. In my case, that would be 4 minutes just as the sun comes over the horizon early in the morning. However, as you will see in the next paragraph, there is practically no shadow flicker at that range.

A wind turbine blade for a 3mw turbine is typically 3.5m wide at its widest part. If the sun was a point source at an infinite distance, it would send a solid shadow 3.5 meters wide to Waipara. The sun is not a point source. It has a width of 32minutes (half a degree) of arc. Light from the edges of the sun fills in the shadow such that a full shadow (umbra) extends 350m beyond a 3.5m wide blade and by that distance the width of the full shadow is zero. At a distance of 5000m beyond the wind turbine, the shadow of the blade has spread out over 46m. Stated another way, the sun intensity will vary for the above mentioned 8 days of the year for 4 minutes in the early morning on those 8 days from full strength to 93% strength. Unless you are very close to a wind turbine, shadow flicker is virtually non existent and even if you are close, it will occur only for the short time that you, the turbine and the sun are perfectly lined up. Some simple graphics in the proposed government paper would explain this to the layman.

(Appendix 2) Aesthetics
One legitimate aspect of the aesthetic fear is the belief that if a wind turbine is visible from a property then the value of that property will decrease. The government should carry out a detailed survey both here and abroad to see if such properties have decreased or increased more or less than other properties in the same area that do not have a view of wind turbines. This would form part of the government report. An item on National Radio a couple of years ago indicated that the price of properties with a view of a wind turbine had actually increased more than the average in Europe.

William Hughes-Games

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