Why arent there wind powered vertical axis boat generators ?

Discussion in 'OnBoard Electronics & Controls' started by rwatson, Nov 25, 2015.

  1. rwatson
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    rwatson Senior Member

    It seems that spinning blades arent a good idea on a boat.

    This version can operate in high winds as well as being virtually silent.

    I wonder why smaller versions couldnt be a good idea for boats ?

    http://www.silentwindturbine.com/products.htm
     

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  2. rwatson
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    rwatson Senior Member

    1 person likes this.
  3. keysdisease
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    keysdisease Senior Member

    Like these?
     

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  4. gonzo
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    gonzo Senior Member

    The noise on wind generators is caused largely by the high speed the blades are turning. A vertical axis generator will also be noisy if it turns at high speed. Also, it is at most about half as efficient as a conventional type. The reason is that the backward turning blades work against the forward turning ones. As far as safety, they may be somewhat less dangerous.
     
  5. philSweet
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    philSweet Senior Member

    A companion question might be why are there HAWTs on boats.:?:
     
  6. rwatson
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    rwatson Senior Member

    Thats some good info.
    I found Kronos on Youtube


    and their web site
    http://www.kronosenergysolutions.com/WindProducts/mastR1.html

    Those inneficiences seem to be the biggest problem, but I suppose you couldnt mount a HAWT on your mast either.

    I also found this one
    http://www.leturbines.com/products/le-v50-wind-turbine/

    No-one gives any hint of prices which is always a worry.


    Phils question on why there are wind generators on boats could be extended to why people put sails on boats. Wind is the least efficient way of creating power from an economic point of view.

    But - it will always blow, long after your wallet is empty, or your boat is a long way from a fuel pump.

    It would be fun to find a good generator and experiment with some variations of balde systems.


    PS - found an interesting article on a quieter blade design for a HAWT,
    https://www.morganscloud.com/2010/05/03/quietening-boat-wind-generator/


    some good data on this thread as well
    http://www.boatdesign.net/forums/boat-design/anyone-heard-mast-r-wind-turbine-44060.html

    a thorough dicussion including indicative prices on the Kronos system here also
    http://www.cruisersforum.com/forums/f14/vertical-axis-wind-turbine-59699.html
     

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  7. CDK
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    CDK retired engineer

    Quote from the LE-turbine website: "The LE-v50 is precision engineered in the UK", so do not expect a bargain!
    Their V-50 model provides 12 Watts in a 16 kn breeze, barely enough to keep a small battery bank charged. It has a rotating part, so it must have bearings and seals, making it far less reliable than a small solar panel.

    It exists, so there must be a niche market for it (?).
     
  8. Leo Lazauskas
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    Leo Lazauskas Senior Member

    That is not correct.

    The blades on the downwind side can extract some of the energy that
    remains after the upwind blades have extracted their component.
    In fact, the well-known Betz limit is slightly higher for VAWT than
    HAWT because of that. (I am here talking about lifting VAWT, not
    drag types like Savonius rotors - they are very inefficient and
    require very strong support structures.)

    HAWT are, however, much better for high-speed applications, like
    driving generators. VAWT tend to reach their maximum efficiency at a
    lower tip-speed ratio (TSR) which is better suited to pumping
    applications and similar.

    One advantage of VAWT is that they are "omni-directional", whereas
    HAWT need to yaw into the wind. That insensitivity can be an advantage
    in tidal streams where the flow direction changes (nearly) every day.

    Another disadvantage of VAWT is that some types are not self-starting.
    They either require auxiliary power to drive them through a dead band
    at TSR=1, or they need to allow the blades to pitch. It is not easy to
    make curved blades pitch on the classic Darrieus (egg-beater type)
    VAWTs. Straight-bladed types can be tuned to reach their optimum
    efficiency at a prescribed TSR, but it makes the whole thing more
    complicated and, as any engineer will attest, that brings with it a
    whole raft of problems.

    VAWT can be made to self-start if they have a high "solidity", like
    the Kronos and others shown by Mr. R. Watson. Unfortunately, that
    reduces their efficiency significantly.

    VAWT need to have good over-speed controls. So do HAWT, but VAWT can
    literally blow apart in very high winds because of the large bending
    moments on the blades. We ran one in a wind-tunnel and had to limit it
    so it wouldn't exceed 200g on the blades. (g = gravitational
    acceleration, not grams!) At 400g we were worried that a blade might
    come off and go through the wind-tunnel walls (and whoever was behind
    them).

    The only hope I see for VAWT are in tidal streams, or gigantic
    turbines where HAWT seemed to have reached a limit. To make HAWT
    larger than the biggest ones now available would require very tall
    towers, and that is a problem because of the large, heavy gearboxes
    etc that have to be at the top of the tower. With VAWT, they can be
    at ground- (or sea-) level, and they would run a little slower so
    they might not need liquid nitrogen cooling which most large HAWT
    have now.

    The best solution for water, (e.g. tidal streams, rivers, etc.) is
    still not settled. We seem to have reached convergence with wind
    applications, i.e. the 3-bladed HAWT, but there are a huge variety of
    candidates being tested in water and it is not clear which type will
    ultimately win out.

    Disclaimer: Although I have been working on the mathematical
    modelling of VAWT for many years, I am not an uncritical enthusiast.
    VAWT are suited to some applications better than HAWT, and are
    inferior for many, many others!

    Lazauskas, L and Kirke, B.K.,
    "Modeling passive variable pitch cross flow hydrokinetic turbines
    to maximize performance and smooth operation",
    Renewable Energy, Vol 45, Sept 2012, 41-50.

    Kirke, B.K. and Lazauskas, L.
    "Limitations of fixed pitch Darrieus hydrokinetic turbines and the
    challenge of variable pitch", Renewable Energy 36 (2011) 893-897.

    Kirke, B.K. and Lazauskas, L. (2008),
    "Variable Pitch Darrieus Water turbines", JSME J. Fluid Sc. & Tech.
    Vol. 3, No.3, 430-438.

    Kirke, B.K. (1993).
    "Experimental Verification of a Mathematical Model for Predicting
    the Performance of a Self-acting Variable Pitch Vertical Axis Wind
    Turbine", Wind Engineering, Vol 17 No.2 pp.58-66.

    Lazauskas, L. and Kirke, B.K. (1992).
    "Performance Optimisation of a Self-Acting Variable Pitch Vertical
    Axis Wind Turbine", Wind Engineering Vol 16 No. 1, pp.10-26.

    Kirke, B.K and Lazauskas, L. (1991),
    "Enhancing the Performance of a Vertical Axis Wind Turbine Using a
    Simple Variable Pitch System", Wind Engineering Vol 15, No.4.

    http://www.cyberiad.net/vawt.htm
    http://www.cyberiad.net/tide.htm
     
  9. rwatson
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    rwatson Senior Member

    Some interesting info in that Leo, thanks.

    I have a whole lot of Googling to do on rotating shrouds and self adjusting blades. There has been a lot of work on VAWT configurations. Interesting stuff.
     
  10. gonzo
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    gonzo Senior Member

    Looks like I have to do some reading to update.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    I suppose when the wind is blowing, and the clouds are blocking the sun....
     
  12. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Gonzo, you only made one fundamental error, and that was thinking that the
    blades on the downwind side can't generate any useful power. You have to
    consider the vectors of the lift and drag forces, and the various velocities!

    As you can see in the attached schematic (with wind coming in from the
    right-hand side), keeping track of those vectors is quite a messy business,
    and more so if the blades are allowed to pitch around their quarter-chords.

    Your statement that VAWT have about half the efficiency of HAWT is not far
    off the mark, for high-solidity VAWT. (They are the most common ones I
    have seen being touted for use on small boats.)

    Solidity = N*c/r, where
    N = number of blades,
    c = chord length,
    r = radius.

    If you reduce the radius in the first schematic it would increase the solidity.
    Increasing chord length, or adding more blades would also increase the
    solidity (and manufacturing costs!).

    The small VAWTs that you see in a lot of advertising material are high
    solidity because that helps self-starting. Unfortunately, high solidity also
    reduces efficiency. Advertising material tends to ignore that!

    The attached graph show the power coefficient (Cp) as a function of
    tip-speed ratio, lambda, (the ratio of the blade speed to ambient wind
    speed). As you can see, the "Mays" VAWT with solidity = 0.75 is less
    efficient and reaches its maximum at a low tip-speed ratio.

    The efficiency of some typical VAWT and HAWT are shown in the last graph.

    At high tip-speed ratios, HAWT are definitely superior. I can't see any other
    type being competitive with them for generating electricity. At the lower
    tip-speed ratios, VAWT tend to come into their own. They can also generate
    larger torque which is better for driving pumps, air compressors etc.

    Another important consideration is the Reynolds numbers that the blades
    operate at. Small turbines will have small blade chords, and therefore the
    Reynolds numbers will be small. That reduces their efficiency enormously. It's
    no wonder that small turbines aren't all that successful. As always, be very
    wary of claims in advertising material!

    Finally, a lot of claims of efficiency are for turbines operating in ideal
    conditions, or based on mathematical models. The real world is a far messier
    place where turbulence, bird droppings, ice,and small dents and surface
    irregularities all act to reduce efficiency further.
     

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  13. Leo Lazauskas
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    Leo Lazauskas Senior Member

    I'm not all that convinced by rotating shrouds.
    If you are going to commit material (especially expensive marine
    metals or composites) hoping to improving the efficiency of a turbine,
    or otherwise getting more power out of it, why not just increase the
    blade length? :)

    For tidal turbines, fixed ducts and diffuser-like structures might be
    worthwhile. Best of all, though, would be to find a natural under-water
    feature (like rock formations or rock-cuttings) that constrict the flow just
    enough to speed it up. Power is proportional to speed cubed, so that's worth
    looking at. Of course, that "feature" must not be too narrow because the
    current will tend to flow around and not through it.

    There has, but as I said in my earlier reply, we are still a long way from
    convergence on a single turbine type, or some other device. Maybe there
    won't be one clearly superior type for generating power because the wave
    environment is so unforgiving. Sea-beds are becoming littered with what
    seemed to be promising candidates, but that were soon smashed into tiny
    pieces.

    A lot of work on marine devices was performed during the 1970's oil crisis.
    Salter's ducks seemed promising, but went nowhere. Many top-knotch
    hydrodynamicists and engineers worked on a variety of ideas for a few years
    and didn't come up with anything that stood the test of time.

    One thing has remained constant: then, as now, there's just as much bs
    flying around. And twice as much just before grant application time ;)
     
  14. rwatson
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    rwatson Senior Member

    Well, blade length may be a major issue in restricted space, like boats etc.

    Shrouds improve efficiency on VAWTS and HAWTS from what I can read, but shrouds on VAWTS arent as space hungry.
     

  15. Leo Lazauskas
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    Leo Lazauskas Senior Member

    Fair points.
    Shrouds on VAWTs would need to be yawed into the wind, which adds to the
    complexity and the VAWT loses one of its inherent advantages over HAWT.
    If the VAWT is on a tower or pole, it would increase the weight at the top, and
    add to the "toppling moment". (Do any engineers use that term?)
    It's certainly an interesting engineering design problem for someone.
     
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