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Comments on domestic wind turbines

I recently looked at a BBC messageboard where there was an interesting discussion about domestic wind turbines and their performance.

Some of the more informed comments are summarised below. It's a pity that the contents of these boards are not kept long, so I've done this page before they disappear.

I have reduced names to initials, and where necessary, made small edits so that each message is self-contained. I do not know how to contact any of the contributors,, but if any person recognises his contribution and wants it removed, please email me; it will be done straight away.

My email address is

suttonelms (at) ukonline.co.uk. I've written it like this to avoid spammers.

N.D.

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G.B.B.: .....I was recently going to go ahead with a turbine but got cold feet and bought a PC interfaced anemometer instead. So far my logged data suggests that a 1kW turbine would generate 30p's worth of electricity per week despite my house being at the top of a south-facing hill.

I have looked at the 'Betz law' used to design current turbines and am unhappy with it. The dangerous assumption in this derivation is the swept area of the turbine, which becomes inaccurate at low speeds due to the low fill factor of the blades.

As a keen sailor, I know that you can still get loads of energy out of low wind speeds simply put putting up a larger sail area and also adding extra shape (curve) to the sails to generate maximum lift. I think that turbine designers and the scientists who advise the government need to get out more.

I am a professional physisist with 20 years experience and I sail to a semi-professional standard.

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A.H.: ....Suppose your average power output is as low as 25W; your yearly available power is still 219KWh (25W times 24 hours in a day times 365 days in a year). Not bad, if you could store this energy for later use.

Now suppose that you use this energy to break up water into oxygen and hydrogen by electrolysis. You could store the hydrogen and burn it when you need energy and/or warmth.

Comment from ND - health and safety implications here ... hydrogen / oxygen mixtures are highly explosive; much more so than natural gas / air.

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M:......I accept the limits of wind turbines, but I do have two worries which caution against completely rejecting them.

First is the experience that when householders start generating electricity, it has an impact on their energy use. Energy stops being meaningless stuff that comes from a wire or a pipe and instead is something you can "see" being generated. It would be great if we could encourage people to stop wasting energy while investing in more efficient generation (like shares in an offshore windfarm, perhaps) or . People like to have something to show for their money; we are all flawed.

Second, I think it is reasonable to make a decision to spend more on a less efficient way of saving energy if it avoids something else we don't like. So if domestic wind turbines are less effective than big windfarms, but less visually intrusive and don't spoil beauty spots, I'm not too hung up about doing the less efficient thing. The extra money required is actually being spent to preserve views - not on climate change, and we shouldn't confuse the two.

Finally, maybe the main benefit of these devices is that people spend money on them instead of the latest plasma screen, extra holiday, or other energy guzzling status symbol. They might not generate as much as hoped - but they may stop using extra energy. I'm worried that fashionable consumption is probably not the long-term way to tackle climate change - but if gives us a short term boost then so much the better.

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T:
I work in a turbomachinery lab. We worked out using some basic Physics that a domestic wind turbine would struggle to generate more than 8 watts on average; an irrelevantly small amount of power.

Worse than this, it represents a unnecessary burden to society because of the waste of materials used in its construction.

There is nothing wrong with distributed power generation. However, its strength seems likely to be when groups of people do something large together, rather than everyone 'doing their little bit' and in the process actually doing nothing useful.

There is a lot of sensible discussion here about how to estimate average energy generation and typical savings over a year or the lifetime of the generator, but none seem to take into account the fact that for much of the time, energy is being generated when there will be no actual demand for it. For example, one assumes the wind turbine is turning at night, when domestic power requirements are at a minimum.

Are these domestic generators supplied with some type of power storage mechanism such as batteries and an inverter, so that none of the power generated is wasted, or am I missing something?

If there is no storage system, then presumably most of these annualised power calculations are way out.

If one did produce such a generator, with batteries for example, has anyone thought to factor in the cost of manufacturing these, from an energy perspective and from also the point of view of the material pollution produced both during manufacture and at the end of its life?

Also, most rechargeable battery systems that I know of have a limited lifespan and lose energy storage efficiency progressively through their life. I donít think they would last over the 10 year period used by many of the calculations here.

Comment from ND - ......some batteries last five years. Most fail way before that.

At the end of it all, Iím sorry to say that I think that whatever we do from a renewable energy perspective these are only short term fixes, as none of these appear to have the ability to generate the vast amounts of energy that the ever increasing population of this planet is likely to require in the future and thatís something that never seems to get talked about.

Just how many wind turbines would it take if (even at current population levels) the entire global population used energy at the rate of a ďtypicalĒ western household? Even assuming that we become more energy efficient, the figures do not make pleasant reading.

We need to look to other higher energy-density power generation solutions. Letís hope that ITER, the new thermonuclear fusion research project, finally gets its act together, proves that thermonuclear fusion power generation is physically practical, commercially feasible and environmentally sound and that in 50 years time we will be running a world hydrogen economy underpinned by that.

If we donít, our children and our childrenís children are in for a very grim time of it.

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