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Wind Turbine?

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  • 08-02-2009 9:19pm
    #1
    bluesguitar
    Registered Users Posts: 43 ✭


    Hey guys
    Just moved into a new house on the northwest coast, where it is always always windy! A friend of mine was telling me he heard of a few people around who have put up wind turbines to power their houses off the grid. I have an average sized four bedroom house and i am liking the idea of being esb free! anyone any suggestions on size or power, makes etc?


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    #2
    quentingargan
    Registered Users Posts: 1,627 ✭✭✭quentingargan


    I make a wind turbine for the Irish market, but I'll PM you about that.

    In terms of size though, it depends on how much you will use yourself, and how much the ESB will pay you for what you sell back. The CER is about to announce a decision on that in the next few days - ESB had suggested 9c. See here for more on that process

    If you have a small turbine and use all of its power, you are saving 16c per kwHr. If you have a large one and are selling most of your power as surplus, then you are only making 9c per KwHr. So you need to assess your needs first before deciding on the size (or wait and see what price the ESB dishes out).

    Planning exemption is quite generous on the size of turbine, but less generous on the height of your tower, which is a pity. I'd prefer to have a 2.5kw turbine on a tall tower than a 5kw turbine on a short one...

    Q


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    #3
    Matt Holck
    Registered Users Posts: 9,706 ✭✭✭Matt Holck


    I checked on wind turbine and
    the start wind speed required to function is 2.5 m/s (6 mph) estimate
    I check San Diego wind speed is 11.5 mphfrom the West currently

    a 12 foot diameter wind blade produces 2.5 kW
    based on a 11 m/s (25 mph) wind speed

    so succh a tower would produce about 1 kW right now in san diego


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    #4
    Matt Holck
    Registered Users Posts: 9,706 ✭✭✭Matt Holck


    opps

    I was measuring the turbine output on a linear scale to wind speed
    when the kinetic energy of the wind is
    E= (1/2)Mv^2
    where
    M is the mass of the passing air which is the volume that passes the blade
    also based on speed v
    and
    v is the velocity of the wind

    anyway
    output is not linear to wind speed at all
    here's a graph of a different turbine output(Watts) versus wind speed(m/2)
    wind_turbine_power_1kw.jpg
    http://www.joliet-technology.eu/wind_turbine_power_1kw.jpg

    so a tower in San Diego might produce 400 watts


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    #5
    maniac101
    Registered Users Posts: 233 ✭✭maniac101


    Matt Holck wrote: »
    opps

    I was measuring the turbine output on a linear scale to wind speed
    when the kinetic energy of the wind is
    E= (1/2)Mv^2
    where
    M is the mass of the passing air which is the volume that passes the blade
    also based on speed v
    and
    v is the velocity of the wind
    Hi Matt. Yes, energy is proportional to the square of velocity. However, the power in the wind is proportional to the cube of the wind velocity. So if the speed is doubled, the power increases by a factor of eight!
    Power = Air density x Swept area x (windspeed)^3
    So an accurate assessment of windspeed is crucial when deciding on the viability of a wind turbine.

    As you've rightly shown, the power delivered by a particular wind turbine will depend on its characteristics, manifested in the power curve above, and will be considerably less than the power in the wind.


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    #6
    quentingargan
    Registered Users Posts: 1,627 ✭✭✭quentingargan


    maniac101 wrote: »
    As you've rightly shown, the power delivered by a particular wind turbine will depend on its characteristics, manifested in the power curve above, and will be considerably less than the power in the wind.

    As a further complication, the mean wind speed for an area doesn't tell you what the average output of a turbine will be. For example, a mean wind speed of 6m/sec could be half the time at 0 and half the time at 12m/sec. At 12 m/sec the output would be eight times what it is at 6. That is an extreme of course, and you normally apply a local curve for the wind characteristics.

    The best calculator I have seen for estimating output for a known power curve and mean wind speed is on the windpower site here

    Q


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    #7
    Cheeble
    Closed Accounts Posts: 224 ✭✭Cheeble


    Don't forget also that the important thing is not how much power the manufacturer claims their turbine will generate, but how much energy it will provide over the course of a year. That includes a lot of time when the wind isn't blowing at 25mph.
    To get an answer to this, you need to multiply the power curve by the wind speed probability curve for your site (normally follows a Weibull distribution). If you take a shortcut and assume you'll get four times the energy at the average windspeed (8*output for 1/2 the time), you'll be poorer, sadder, and wiser in a year's time.

    There's a lot of hype around microgeneration at the moment, be realistic in your expectations. In a UK survey over the last year, the average annual generation was about ten euro worth (at 19c/kWh) for the whole year.

    wind_speed_probability.jpg


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    #8
    quentingargan
    Registered Users Posts: 1,627 ✭✭✭quentingargan


    Cheeble wrote: »
    In a UK survey over the last year, the average annual generation was about ten euro worth (at 19c/kWh) for the whole year.
    I quite agree. There were some practices in the UK that are horrifying. B&Q and several others were selling ridiculous turbines that you bolt to your chimney and David Cameron was one of the more high profile buyers of such a system (you can see the photo here). Turbines need clean air and don't work in that sort of situation.

    I've gone into this on my own blog here - It is fine having a turbine and knowing that the payback time is dreadful if that is what you want, but I hope the new ESB feed-in tariffs don't herald the launch of more double glazing sales types flogging turbines into useless sites. That's a waste of steel and concrete and the carbon payback may be questionable too... :mad:


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    #9
    Matt Holck
    Registered Users Posts: 9,706 ✭✭✭Matt Holck


    I was wondering if a wind mill could be made of cheaper material like canvas sails


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    #10
    quentingargan
    Registered Users Posts: 1,627 ✭✭✭quentingargan


    Matt Holck wrote: »
    I was wondering if a wind mill could be made of cheaper material like canvas sails
    Nice thought, but 'fraid not. The costs are roughly 30% tower, 40% electronics and 30% generator and blades, of which the lions share is the generator.


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    #11
    Matt Holck
    Registered Users Posts: 9,706 ✭✭✭Matt Holck


    maybe some car factories can bring the production down on generators
    maybe existing electric towers can serve as mounts for a start


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    #12
    Cheeble
    Closed Accounts Posts: 224 ✭✭Cheeble


    Canadian Patent Application (WO2008058382) by Darryl Jessie suggests putting VAWTs on utility poles:
    jessie.jpg
    Regarding canvas sails, the performance of a fast spinning turbine depends a lot on the blade lift to drag ratio. It would be difficult to get canvas sails to match the aerodynamic efficiency of the smooth surfaces available using aluminium or gel-coat. Even dust build up can measurably reduce performance, so it's important to keep your wind turbine clean!

    The cost of generators might come down a little in volume, but not by enough. Probably the biggest target for cost saving would be the electronics. Grid tie inverters in particular seem to me to cost far more than they should.


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    #13
    Matt Holck
    Registered Users Posts: 9,706 ✭✭✭Matt Holck


    rid tie inverters in particular seem to me to cost far more than they should.

    power companies may resist power generation becoming decentralized


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    #14
    Cheeble
    Closed Accounts Posts: 224 ✭✭Cheeble


    Quite so, this is taken up on another thread:
    ESB offers 9c to micro-generators


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