Looking for direction with a low wind generator

spiral_72
spiral_72 Registered Users Posts: 3
I've been poking around all over the internet. Maybe this is a case of I don't know what I'm looking for. South Carolina really has light winds, an average of 5mph - 10mph depending on the month. Obviously this is far too low to generate useful power with a turbine. I have some ideas but surely they are not new ideas. I'm posting here is see if anyone has search terms, keywords or links they would share for a low power station.

I'm thinking horizontal shaft, wind sail type of thing, built similar to a squirrel cage. Wind even at this low speed still has plenty of energy to offer, I just need a large surface area to generate torque instead of spinning blades at several hundred rpm. I'm thinking if I build a shroud hiding the bottom half, redirect that wind upward to the top sails it might work. The prototype would be of PVC and plastic sheeting and generate no power. If it's stupid tell me. The idea come from a Pelton wheel. Air is a fluid, why not?

Anyways, I'll check back or post any more thoughts.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,404 admin
    Welcome to the forum.Spiral.

    The fundimental question is "how much power at what wind speed" do you need to make this a "useful to you" type project?

    A little math.. The power in wind goes with the cube of the wind speed. If you have a turbine that is designed to produce 100% of rated power at 25 MPH wind, then at 5 MPH it would generate:
    • (5mph)3/(25mph)3 = 1/125 = 0.008 = 0.8% of rated power
    • Need a 125x the area of a "normal turbine" to produce "equal power" at 5 mph
    • sqrt (125) = ~11x the swept diameter (blade diameter) to harvest "equal power" at 5 mph
    So the first problem is that 5 mph wind has almost no useful energy.

    The second is that you need to get the turbine up high so that it is not in turbulent air flow (buildings, trees, etc.) that are upwind of the turbine. In general, that is a minimum of 30-60 feet off of the ground.

    The third--Most areas have strong winds during stormy weather--That turbine that can generate "useful power" at 5 mph must remain "safe" in 40-80+ MPH winds (depending on where you live).
    • (80mph)3/(25mph)3 = 1/125 = ~33x rated power
    • 33/0.008 = 4,125:1 ratio of Max available power to "useful power"
    So--I will not tell you "it cannot be done"--It really depends on how much energy at 5 mph you need (10 watts vs 1,000 watts) to figure out the basics of how large the turbine needs to be.

    Then you need to figure out how high to mount and protect it against bad weather.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • spiral_72
    spiral_72 Registered Users Posts: 3
    Yessir, thank you. I have really given up on the standard turbine style three (or five or...) bladed generators. With the exception of a storm we have little wind here. 5-7mph is fairly predictable.

    I suspect technically if a wind turbine were large enough, the 0.8% you offered would power my home, but not really practical with a never payback. The difference in a small residential type turbine and the large megawatt brothers is collector area. Have you ever heard of, or have a definitive reason why the horizontal shaft squirrel cage sail thing won't work? Maybe a paddle wheel would be a better description. I could make a drawing if it'll help.

    This is what give me the idea: https://upload.wikimedia.org/wikipedia/commons/9/97/Pelton_wheel_turbine_in_Barcelona.jpg
    The "cups" would be very wide, maybe 8ft wide, 2ft tall. I haven't made a drawing but I expect to have about six "cups" gathering 16sqft of wind at 5mph. The pelton wheel is so efficient in that the majority of the water pressure is transferred to torque meaning if the water velocity were 5mph (2.2m/s) the output velocity should be near zero. Wheel speed would be fairly slow, MAYBE 60rpm, through a step up gear, belt/pulley whatever to an electric generator of some sort. I have calculations to do, however 1kw/hr would be lovely. Maybe it's all a huge waste of time.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Sorry to say, many of us including me, have been around the block with small scale wind, and finally learned enough to step away and move to far, far more productive, safe and trouble free solar electric panels. And yes, they will, except for heavy overcast, produce power even on cloudy days.
    I did keep the alternator from my wind turbine though (gave the rest away) and have been using it on my micro-micro hydro system for 6 or 7 years now.
    One thing positive I can say about the wind turbine I had though is - - it was wonderful to lay back in the grass and watch it spin against the clear blue sky- - even if it wasn't producing any useable power. It was very relaxing to do that.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    ...
    One thing positive I can say about the wind turbine I had though is - - it was wonderful to lay back in the grass and watch it spin against the clear blue sky- - even if it wasn't producing any useable power. It was very relaxing to do that.
    Until one of the blades comes off, of course.
    SMA SB 3000, old BP panels.
  • spiral_72
    spiral_72 Registered Users Posts: 3
    AH phooey. Alright. I'll check back in case anyone chimes in with POSITIVE comments ;) I really thought it might work well but as much time as I spent researching the thing I suppose there's a reason I couldn't find anything.

    Thanks y'all. I really appreciate your time. I built a solar air heater that will run you out the living room, but it's not the season for that. Guess I'll go start on my revision #2 water heater, but that's not near as interesting as the wind power.:p
  • Belmont Solar
    Belmont Solar Registered Users Posts: 26 ✭✭
    Sorry to say, many of us including me, have been around the block with small scale wind, and finally learned enough to step away and move to far, far more productive, safe and trouble free solar electric panels. And yes, they will, except for heavy overcast, produce power even on cloudy days.

    Very, very true. Solar may not seem as interesting while in the imagining stage. But solar produces more power per $ invested, and is much, much more durable.
  • Cski
    Cski Registered Users Posts: 11 ✭✭
    spiral_72 wrote: »
    AH phooey. Alright. I'll check back in case anyone chimes in with POSITIVE comments ;)
    I can't give you any in put on your design, but I would say to try and experiment. You may be the one to design an efficient wind generator for low wind speeds and become rich. Think were we would be if Tesla and Edison gave up :). Good luck.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Unfortunately the researchable literature is not full of failed experiments to show you exactly what does not work. Just theoretical analyses of why low wind speed is such a problem.

    I do not recall seeing an analysis of the Dutch windmills or what wind speeds they need to work. They are a very large sail area and slow rotation. (But rather expensive to construct in terms of the supporting structure.
    SMA SB 3000, old BP panels.
  • todayton
    todayton Registered Users Posts: 1
    Orlando Sanchez wind turbine YouTube
  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    spiral_72 said:
     Wind even at this low speed still has plenty of energy to offer, I just need a large surface area to generate torque instead of spinning blades at several hundred rpm.
    Unfortunately the only two things that really matter in terms of how much energy you can harvest from wind are swept area and windspeed.  There are no good "tricks" that allow you to get more energy from low wind if you cannot increase the swept area.  (For some reason this comes up again and again; people think that if they can just come up with a good design they can beat the swept-area rule.  I've never seen a design that accomplishes that.)
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    spiral_72 said:
     Wind even at this low speed still has plenty of energy to offer, I just need a large surface area to generate torque instead of spinning blades at several hundred rpm.
    Unfortunately the only two things that really matter in terms of how much energy you can harvest from wind are swept area and windspeed.  There are no good "tricks" that allow you to get more energy from low wind if you cannot increase the swept area.  (For some reason this comes up again and again; people think that if they can just come up with a good design they can beat the swept-area rule.  I've never seen a design that accomplishes that.)


    Aside from the expense of building a large swept area wind power collector, there is the really serious problem of what to to during the occasional period of high wind.
    Either you have a 100% reliable furling system, a great hulking braking system or a turbine prone to spontaneous rapid disassembly. (Got that euphemism for explosion from a battery forum.)
    SMA SB 3000, old BP panels.