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  1. #11
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    The cheapest wind generator you can get in nz is $585.
    It generates 200w at 40m/s wind speeds.
    To get 1kw you need to have it running for 5 hours at top speed.

    To buy 1kw hour off the power grid is only 17c.
    I believe wind generator's have very poor rate of return for the investment.


  2. #12
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    Pimpit - is that to buy outright? How long does it last?. My calcuations show it needs to survive for 2 years running at full speed non stop to break even. However, you would only get that if you weren't connected to the grid. To connect to the grid (because you are to far away) may cost $1000's. Plus, i assume they get more efficent as they grow bigger.

    Wind (large scale)is currently bordering on being economic (otherwise they wouldn't build them). IF carbon taxes were introduced this should improve.

    I though one of the problems with Nuclear is that it is just to big for NZ. ie One normal size station will supply the majority of our power needs, making transmission a major problem, and the major issues when you close it down (ie for maintenance or meltdown) if the majority of the country is relying on it.
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  3. #13
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    quote:Originally posted by pimpit

    The cheapest wind generator you can get in nz is $585.
    It generates 200w at 40m/s wind speeds.
    To get 1kw you need to have it running for 5 hours at top speed.

    To buy 1kw hour off the power grid is only 17c.
    I believe wind generator's have very poor rate of return for the investment.

    40m/s = 144km/h

    BTW Are we talking about the windmill or the cow?
    om mani peme hum

  4. #14
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    quote:Originally posted by duncan macgregor

    Lot of proving to be done before i invest in this one. Meridian and trustpower both questioned the two blade British design before it blew its self to bits. I dont care if it was a one off shows a lack of understanding.
    NZ Windfarms are running open days the last three Sundays in November. So yesterday I went along to check the Gebbies Pass site out myself. It was quite refreshing in that instead of facing off to some media drone, you get to speak to the people who are actually driving the project, Chris Freear and/or Geoff Henderson face to face. In other words you get to ask the tough questions to the people who should know the answers, and are not fobbed off with some platitude! There is one open day left, Sunday afternoon next weekend (27th November), for those who haven't been up there to see it. The Windflow Turbine Site is normally closed to the public, (it's on private land) so I would encourage those who have some interest in power generation in general, as well as Windfarms in particular, to go out and have a look for yourselves.

    Anyway, here is the theory behind the two bladed design. Over the wing span of the Windflow blade (which is reasonably large, comparable with a Boeing 737) the wind is not pefectly steady. Generally one side of the blade will have a slightly different wind force on it compared to the opposite side. There are two obvious ways to overcome this.

    1/ Build the whole windmill structure to be enormously strong so that it can resist any wind nonuniformity - this is the path followed by the three bladed windmill designs.

    2/ Adjust the pitch of the blade on either side of the (two bladed) windmill so that wind of different strength on each side of the blade produces a 'balanced' force on each side of the blade. This is the so called 'teetering' design. Doing it this way means that the whole tower structure can be lighter (less wind forces to resist) and therefore cheaper to make.

    Now why can't a three bladed windmill 'teeter'?

    Imagine you are on a 'see-saw' with 'big lump you' on one end and a light weight kid on the other. Even though there is a severe weight imbalance you can use your legs to 'regulate' the movement of the see-saw to give the kid a good ride. This is analagous to the two bladed windmill design with an unbalanced load on each blade.

    Now imagine a different kind of 'see-saw' analagous to a three bladed propellor. In this design of see-saw there are three sitting positions spread evenly about the circumference of an imaginary circle - all at 120 degrees from one another. There is a single central pivot point, with 'Mom' 'Dad' and 'Kid' equally spaced around the circumference. Now you can see that 'Mom' and 'Dad' have to co-ordinate their efforts together to give the Kid a good ride. Now imagine that Mom and Dad and the Kid are suddenly swapped around from blade to blade. Even worse, their weights are randomly swapped around so that sometimes all three weigh as much as Dad, sometimes there is effectively 'one adult and two kids' and all the other weight combinations are cycled through on a random basis. Can you imagine trying to give a kid a good see-saw ride in that situation?
    It would be almost impossible!

    Of course balancing the wind forces on a two rotor wind blade isn't trivial either, but it is much easier than trying to do the same on a three bladed design.

    Two other things make this project more viable than your average kiwi creation that comes out of the garden shed.

    1/ You don't have to 'sell' the end line product. That's because there is already an established market for power so the risk of 'market failure' is as close to nil as you can get.
    2/ The break even point of the technology, from a production basis, is as low as 60 units. IOW for the thi
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  5. #15
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    RIGHT Snoop now you are Balanced is it a BUY or NOT .. [8D]

  6. #16
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    SNOOPY, Good post thanks for the explanation. I am inclined with the little bit of engineering study i did to still question two blades instead of four, or more. Its a bit like a car engine two cylanders vibrate more than six. The Dutch windmills had four blades never two i still am inclined to think that they have it wrong. My limited knowledge in this field tells me they have it wrong, the more blades the less noise, and vibration the blades can still be feathered in strong wind gusts. I wont buy in i am already exposed with TPW in this field but will keep an open mind on the company.
    macdunk

  7. #17
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    quote:
    Now why can't a three bladed windmill 'teeter'? ...

    ... Of course balancing the wind forces on a two rotor wind blade isn't trivial either, but it is much easier than trying to do the same on a three bladed design.
    Is this what they actually told you Snoopy?

    Hinging rotating blades is a common practice to cope with differential and varying loads across multiple blades. The single (lifting) rotor helicopter did go really anywhere until this idea was applied.
    The advantage of the windflow two blade design is the simplicity of the hinging mechanism. However using a constant velocity joint sort of arrangement it could be applied to a three or (to keep duncan happy) four or whatever blade design. The theory is simple the actual practice of applying it to several tonnes swirling round a horizontal axis is a little! more involved.

    You may also be interested to know that the rotor (independent of the number of blades) balances itself out without any clever control device.

    The big issue here, which blew the prototype apart, is that it can only cope with a finite degree of imbalance (upto when the hinge reaches the limit of the hinge movement). Exceed that and you need to go out and pick up the pieces.
    om mani peme hum

  8. #18
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    quote:Originally posted by Paper Tiger


    Is this what they actually told you Snoopy?
    Not in those exact words. You got the output from the Snoopy 'paraph****ometer'. The see-saw analogy was mine.

    quote:
    Hinging rotating blades is a common practice to cope with differential and varying loads across multiple blades. The single (lifting) rotor helicopter did go really anywhere until this idea was applied.
    The advantage of the windflow two blade design is the simplicity of the hinging mechanism. However using a constant velocity joint sort of arrangement it could be applied to a three or (to keep duncan happy) four or whatever blade design. The theory is simple the actual practice of applying it to several tonnes swirling round a horizontal axis is a little! more involved.
    I appreciate your powered flight acumen on this matter Paper Tiger.

    However, what I think the Windflow people were trying to tell me (and I stand to be corrected) was that a wind turbine tends to be an order of magnitude larger than these transport applications. So the differential blade loading of wind gusting is much more of an issue.

    Also with a plane or a chopper you can simply 'go with the flow' if a really strong gust of wind gets up. A wind turbine is anchored to the ground and so it must take the full force of whatever the wind throws at it.

    quote:
    The big issue here, which blew the prototype apart, is that it can only cope with a finite degree of imbalance (upto when the hinge reaches the limit of the hinge movement). Exceed that and you need to go out and pick up the pieces.
    The wind turbine is programmed to shut down above a certain wind speed. I think I am correct in saying that it was stationary when it blew apart. The Windflow people know this because of the electronic data logging equipment on it. Something was mentioned about the bolting assembly on the nacelle being redesigned.

    SNOOPY

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  9. #19
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    quote:Originally posted by duncan macgregor

    SNOOPY, Good post thanks for the explanation. I am inclined with the little bit of engineering study i did to still question two blades instead of four, or more. Its a bit like a car engine two cylinders vibrate more than six.
    I don't think your analogy is quite right Macdunk. Car cylinders are generally in different geometric planes turning a crankshaft. It is the out of balance forces and moments in the different geometric planes that gives an internal combustion engine its balance (or not so to speak). IIRC the 'straight six' cylinder engine is a theoretically perfectly balanced layout, whereas any smaller number of cylinders, or a V6, is not.

    The windmill blades are all in one geometric plane.

    Perhaps a more valid comparison would be with a radial aero engine. I don't think it matters much how many cylinders you have in a radial aero engine. It won't have large out of balance forces operating inside it.

    quote:
    The Dutch windmills had four blades never two I still am inclined to think that they have it wrong.
    There may be some argument for four blades being more efficient. Certainly the commercial prop aircraft I see tend to have four blades and not two.

    However, in the case of a wind turbine the power source is 'free', so efficiency isn't the number one goal. The goal is to extract as much power as you can from the wind available, and that can but doesn't always mean working your blade at maximum efficiency.

    Of course if you had four blades, then the total blade structure you are supporting would be twice as heavy, and that has other implications for costs.

    quote:
    My limited knowledge in this field tells me they have it wrong, the more blades the less noise, and vibration the blades can still be feathered in strong wind gusts.
    The 'noise point' was brought up. There is no denying that wind turbines do make a noise. The plan is to keep the noise 'broad spectrum' wherever possible. That means no annoying 'high pitched whine' or 'deep rumble'. Standing right next to the device -in admittedly low wind- we got a periodic 'deep woosh' as the blades went around. I wouldn't describe it as unpleasant any more than the sound of waves crashing in on a beach is unpleasant. Since 'the crash', Windflow have had another look at the gearbox design and have been able to make it quieter. I wasn't aware of any gearbox noise last Sunday, but that could be because the blade speed was so low on the day.

    Having said that, noise annoyance can be a subjective thing.
    The two houses that were closest to the turbine had no problems with turbine noise. The third closest house did. I for one would not be game enough to go and tell he/she of the third house that they are wrong.

    quote:
    I wont buy in I am already exposed with TPW in this field but will keep an open mind on the company.
    Fair enough. Once the business model is proved you may find that NZ Windfarms will be 'put on the block' and a company like Trustpower might end up owning them anyway!

    SNOOPY




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  10. #20
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    Snoopy:
    It would be worth your while reading the WTL report on the event.
    The turbine was rotating (but shutting down). I accept that this was an extreme event and understand what they have applied various remedies and that you can not cover every eventuality.

    PS You do not need to be corrected.
    PPS I have worked out what a paraph****ometer is, don't you just love the american's sense of sensibility and decorum?
    om mani peme hum

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