Calculating Small Wind Turbine Power Production

JayboyJayboy Registered Users Posts: 24
Hi Guys

I have confused myself.
I have a wind turbine that produces 500W at 5ms-1 wind.
To calculate the power output per month do I simply take the Average
Wind speed (m/s) for the month and reference it to the power output ?
How does this calculation work? Can you give me an example for a month?

What is the Wind probability Beaufort (%) factor? And does is factor in?
Thanks Guys


  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Calculating Small Wind Turbine Power Production

    Hi Jayboy, welcome to the forum.
    Double wind speed gives you 8 times the power. Cut the wind speed in half and you likewise get only 1/8 the power.
    How "small" is your wind turbine? Make and model?
    I have some far less than stellar experience with small wind machines. HUGE promises from retailers and manufactures, other than that, all but useless in other than during hurricane conditions that threatened to rip them apart.
    Seriously, at 5 m/s - - - 11 MPH, you can expect next to nothing, or nothing at all in useful energy output. But the hyped up sales info will never tell you that.
    Some good info here:

  • JayboyJayboy Registered Users Posts: 24
    Re: Calculating Small Wind Turbine Power Production

    Thank you for your reply.
    I am more interested in the theory behind the estimate.
    Say in a perfect world' how does one use the average wind speed and beufort probability scale ?
    Thanks Guys
  • BB.BB. Super Moderators, Administrators Posts: 31,614 admin
    Re: Calculating Small Wind Turbine Power Production

    Basically, you want the average energy (speed) based "cubed" wind speed... 1 hour at 20 mph will generate 8x as much power (or more) than 8 hours at 10 mph.

    Most wind turbines tend to generate a "useful" amount of power around 12 mph...

    The "wind turbine power tables" are usually based on something like 12 MPH average 24 hours per day * 30 days per month.

    To get that amount of continuous/stable wind--You are talking about a minimum of a 60-90 foot tower. Commercial based wind maps are based on something like 125 foot level winds.

    Bergy Wind has some interesting spread sheet models you can play with and see how things may work in your place as you play with a few parameters:

    To see how high a tower you may need, go fly a kite. See how high the kit needs to be to fly "stable" (above turbulence). Flying a turbine in turbulent air is pretty much a waste of time and money.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JayboyJayboy Registered Users Posts: 24
    Re: Calculating Small Wind Turbine Power Production

    Hi BB

    Thanks, See the attached Picture.
    Based off the wind data for September.
    Attachment not found.
    In a perfect world. Say a turbine does 500W @ 5ms wind.
    How do I go about the calculation too see how much power it will make in the month of September?
  • Ralph DayRalph Day Solar Expert Posts: 940 ✭✭✭✭
    Re: Calculating Small Wind Turbine Power Production

    I'm not sure about predicting output, but my SWWP H80 (1kw turbine) produces from 520kwhr to 650kwhr per year with 9 years data accumulated. Area is Trenton/Bay of Quinte (Lake Ontario). Usually about 20-24% of my total renewable energy input (2.1kw pv, 1kw turbine). In other words, don't expect a lot. (That 20% helps when the sun is absent)

  • GrinninGrinnin Solar Expert Posts: 39
    Re: Calculating Small Wind Turbine Power Production

    I haven't seen mention of cut-in speed. A generator can be optimized for a particular wind speed but these small ones are not very adaptable. (Huge ones can change the blade pitch.) Some will start generating at lower wind speed but they won't make nearly as much electricity at higher wind speeds.

    As BB mentioned, the real power comes at higher wind speeds. So a generator that won't make any electricity until the wind is fairly strong can actually make more electricity during a year than one that spins more often.

    So your wind generator has a particular curve of wind speed vs watts. You really need to compare that curve to the wind on your site to find out how much time your generator will be most productive.

    (Disclaimer: The generator I carved and wound has been on the test tower, but has never been above the trees.)
    Attachment not found.
  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: Calculating Small Wind Turbine Power Production

    Average wind speed at a site is useless for calculating the power output of a wind turbine. You need:

    1. the graph or equation of the wind turbine's power output verses wind speed; and

    2. the graph of wind speed at the site verses time.
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