wind energy

Discussion in 'General Science & Technology' started by leopold, Dec 18, 2008.

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  1. leopold Valued Senior Member

    let's discuss the design of a wind driven electric generator capable of supplying power for a small farm.
    first we must have a ready source of wind.
    second we need a suitable propeller.
    third we need a suitable generator or alternator.
    fourth we will need some sort of storage system to store power when there is wind but power isn't needed.

    there will be other elements to this scheme such as a transmission and a way to disconnect the generator from the batteries when there is no wind to prevent drainage.

    let's see if we can come up with a cost effective system.
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  3. cosmictraveler Be kind to yourself always. Valued Senior Member

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  5. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    The OP forgot to mention one very important "need" - self protection in strong winds.

    The power of the wind goes as the cube of the wind speed.* Thus, a machine designed to produce full generator output in say 15 mph wind will be 216 times overpowered when the wind is 90mph. No energy generating system, I know of can survive even a 10 times full power, overload. Thus, some way to shed the wind’s power is essential. (I doubt that the drive shaft in a car (or the crank shaft in the motor) can avoid failure even only if torqued at twice max rated torque.)

    Big machines can "feather" their blades so that the torque is reduced by a factor of 100, but this complexity is not (usually) economically feasible on small machines for a farm. The old multi-bladed farm water pumping wind mills are very inefficient. Efficiency decreases as the number of blades increase. (Only one blade, with small counter weight for balance is the most efficient of all but at least 3 blades are need to not self destruct in gusts, so all machine for power generation use 3 blades.) There was so much air friction with all the blades of the old style water-pump wind mills that in high winds the air essentially flow stalled instead of flowed thru the blades. - Effectively most of the incoming air was flowing around an egg shaped, nearly stagnate, zone. That is how they survived but at the price of very low efficiency (~5% as I recall, but the farmer wanted torque in low wind speeds, not efficiency, so many farms used ~32 blade machines.)

    Many years ago, I ran a field test program for the US Coast Guard. (When oil fuel for a remote light house is delivered by CC cutter's helicopter in barrels, the cost per gallon is on the order of $3,000/ per barrel so it was not hard to show that great savings were possible. Many lighthouses have no beach for small boat, instead of a helicopter, but not using it when waves and shore line permit is a significant savings. Deliver of oil for the diesel often doubles as a training mission.)

    I selected a wind generator from company called "North Wind" because it had a clever, very reliable way to shed power. (It also had about the correct max power output, a few KW as I recall.) The rotation axis of the generator was normally horizontal and above a “pivot point.” A stiff many-turn flat coiled spring normally held that shaft horizontal, but the rearward pressure force on the blades in high winds times the elevation of the shaft above the pivot point could lift that rotation shaft up from horizontal.

    I once saw that shaft nearly vertical so the blades were nearly horizontal - presenting very little cross section to the oncoming wind. - An extremely simple, impossible to fail, power shedding system. I do not know if North Wind still exists (PROBABLY has become part of some bigger firm, or if this simple highly reliable system is still commercially available - perhaps someone will search.)

    Summary: AVOIDING SELF DESTRUCTION in strong winds is essential.

    Why 3 blades needed:
    With only 2 (or one) blade there is an axis along the blades with essentially zero moment of inertia against rotation. Thus, a violent gust can produce rapid angular acceleration of the blades in that low inertia rotational axis. There is considerable angular momentum in the spinning generator that is resisting this rapid acceleration. To avoid shaft damage, such as bending or snapping off, there must be some inertial in the blade structure as well. Three blades is the smallest number of blades that has rotational inertial for all possible gust torques on the blades. Every added blade, does add air friction drag so only one blade is the most efficient (until it breaks in a gust). Basically same reason why no one makes bi-wing airplanes any more – too much drag. (But they do have the needed lift at lower speeds.)
    *Wave power also scales as the cube of the wave height. I do not hold much hope for economical (30 year life cycle costs) for most wave machines because many do not appear to have any way to avoid self destruction. I suspect, the some “OK, it is time to sink down to the bottom and ride this storm out” system will be required if 30+ year life-times are to be achieved. The power of storm produced waves is hard to appreciate, unless you have seen an island cut into two pieces or totally destroyed.
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  7. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    I like them too as the generator weight is near the ground, but that generator must also serve as a motor to get them started - they will not self start in even the strongest wind. Their "tower cost" is almost nill as basically it is just a set of guy wires holding the top in place.
  8. mikenostic Stop pretending you're smart! Registered Senior Member

    How big are we talking about? And how big of a prop would you be thinking of for a farm?
    I'll use the propeller from a C-130 cargo plane as an example. Their prop diameter is something like 12 feet (each blade is about 6 feet long). Those kinds of props are called 'constant speed' props. C-130s can also 'feather' their props, like in cases where an engine goes out.
    A constant speed prop like one from a C-130 might work for a farm.

    A bit OT but, that's not the only reason, or even the main reason. At the time, manufacturers just didn't have the technology to make monoplanes with wings to handle the stress of flying.
    The biggest reason for the biplane design was for load bearing, as single wing designs back in that day just weren't strong enough.
    The monoplane design reduced drag, but it also reduced weight.
    Last edited: Dec 18, 2008
  9. scorpius a realist Valued Senior Member

    forget about the stupid overly complicated propeller blade designs,

    vertical axis is the best way to go,
    as this European design proven over a long time in worst of weather conditions shows

    Why The Windside Wind Turbines are the best on the market?

    Quite simply Windside Wind Turbines work when others don’t ! In the gentlest of summer breezes and in violent winter storms. When others fail due to frost, ice, snow or high winds Windside Wind Turbines continue to produce.
    Windside Wind Turbines will produce at least 50 % more electricity in a year than traditional propeller models. Many things make the Windside Wind Turbines extraordinary and their total life cost make them the best value for money.
  10. scorpius a realist Valued Senior Member

    unless you live in VERY windy area,a wind generator itself won't be enough to supply all your power needs....(may need 2 or 3 of those!)

    solar PV panels in combination with wind generator,may be able to,assuming you use the most energy efficient appliances.

    deep cycle batteries are the only ones that can handle the power storage task,right now...
    Lithium-Ion batteries like those used in hybrid electric vehicles may be even better,assuming you can find someplace where you can buy these.

    heres something interesting, to trip on..
    hydrogen powered house,
    bit expensive for my taste but completely independent

    also.. the better solar panels are coming:
  11. mikenostic Stop pretending you're smart! Registered Senior Member

    How long have those types of windmills been around?

    The reason I ask is, just outside of Palm Springs, CA there are dozens of wind turbines. These are the ones on the 150-200feet tall pedestals with the three blade props with each blade being at least 75 feet long.

    You may not know but I'll ask anyway, if the vertical axis turbines are the way to go, and they've been around for as long as the giant horzontal axis turbines, then why didn't California opt for those instead?
  12. scorpius a realist Valued Senior Member

    not sure,why not drop them an email and ask
    damn if I know..LOL
    maybe b/c they do look more impressive,

    maybe whats not invented in America aint very popular,
    maybe its Americans Big Ego standing in the way!

    and maybe the greenies dont have a brain worth of practical thinking,
    as long as the Guvmint throws out the $$$ they will be glad to spend it creating monstrosities.

    instead of building these huge wind farms why not put couple of these QUIET Vertical ones on every houses roof and few PV panels and few batteries and youd be completely self sufficient in electric power,..

    naw that makes too much sense,,

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  13. mikenostic Stop pretending you're smart! Registered Senior Member

    They may look more impressive, but if they are more expensive and less efficient than the vertical axis turbines, their appearance becomes a moot point in my book.

    True dat. But they should be using common sense as well. And if I was a gubmint throwing out money to organizations for a cause, they better be producing something worthwhile.
    Cost effectiveness and efficiency should be just as big a part of 'green' as being environmentally conscious.

    If you're talking individual homes, then I have to concede that solar panels is the way to go. While the wind does blow here in TN, the sun tends to be much more prevalent.
  14. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

    I do not know anything specific, especially about C-130 props, but suspect that if you could get one surplus, cheap that might be a good approach. It of course is only a tiny part of the entire system. The average load, the batteries capacity, the average wind power available etc. all need to be part of a well designed system.

    The first flight was by Santos Dumont, (a Brazilain, but long time resident of Europe, especially Paris region.) He took off from a level field in calm air, climbed up some meters, flew with control in level flight and then landed. (The Wrghts never did any of this.)

    The Wright Brothers once got lifted up by a gust of wind as they rolled down a hill* on rails but never even reached their starting altitude - more like the flight of a powered downhill glider. The reproduction craft, 100 years later, even with better fuel and a somewhat better HP to weight ratio, only rolled down hill into a fair breeze but could not even get off the rails. (It lacked a lucky gust.) Only five people claimed to have ever seen the Wright's plane "fly." Santo Dumont's several flights, from a field near Paris were witnessed by thousands. Almost all the world, except the USA, recognizes Dumont as the first to fly.

    He was also the first to run a hydro-plane boat and achieved 100km/hour with it! It had a 12 cylinder / 200HP motor and under water wings. He used it to better understand how the shape of the wing gives lift. (The Wrights were better theoretical scientists - they carefully did wind tunnel experiments and mathematical analysis to learn how to design wings. They even discovered some error in some of the air characteristic tables they were using.) Their control system ("wing warping") was better too.

    Santos had a canard out front that he could tilt slightly to steer, but that is an inherently unstable system. (He must have been a good pilot. On the 100th anniversary of his flight several replicas were built and flown, but one went unstable and crashed and others were then modified to give some tail control steering which the original did not have.)

    Santos also made the first mono-wing plane, very early (before 1908, I believe). Here from Wiki (Entry = Santos Dumont) is some text about it:

    "... Santos-Dumont made other contributions to the field of aircraft design. He added movable surfaces, the precursor to ailerons, between the wings in an effort to gain more lateral stability than was offered by the {original} 14-bis wing dihedral. He also pushed for and exploited substantial improvements in engine power-to-weight ratio, and other refinements in aircraft construction techniques.

    Santos-Dumont's final design was the Demoiselle monoplane (Nos. 19 to 22). ... The fuselage consisted of a specially reinforced bamboo boom ...The Demoiselle was controlled in flight partly by a tail unit that functioned both as elevator and rudder, and by wing warping (No. 20).

    The high-wing Demoiselle aircraft had a wingspan of 5.10 m and an overall length of 8 m. Its weight was little more than 110 kg with Santos-Dumont at the controls. The pilot was seated below the fuselage-wing junction, just behind the wheels, and controlled the tail surfaces using a steering wheel. The cables supporting the wing were made from piano wire. Initially, Santos-Dumont used a liquid-cooled Dutheil & Chalmers engine rated at 20 hp (15 kW). Later, the inventor repositioned the engine to a lower location, placing it in front of the pilot. Santos-Dumont also replaced the former 20 hp (15 kW) engine by a 24 hp (18 kW) ... This version received the designation No. 20.

    Due to structural problems and continuing lack of power Santos-Dumont introduced additional modifications in Demoiselle's design: a triangular and shortened fuselage made of bamboo; the engine was moved back to its original position, in front of the wing; and increased wingspan. Thus, the No. 21 was born. The design of No. 22 was similar to No. 21. Santos-Dumont tested opposed-cylinder (he patented a solution for cooling this kind of engine) and water-cooled engines, with power settings ranging from 20 to 40 hp (30 kW), in the two variants. ...

    The Demoiselle airplane could be constructed in only fifteen days. Possessing outstanding performance, easily covering 200 m of ground during the initial flights and flying at speeds of more than 100 km/h, the Demoiselle was the last aircraft built by Santos-Dumont. ..."

    The photo of the Demoiselle in Wiki does not show how Santos made the mono-wing plane. (Solved your "structural concerns") There was a vertical post with piano wire cables to help hold the wing weight when still not moving fast.

    One thing wiki dose not even mention is that everyone, including some Americans by the name of Boeing, understood Santo's monoplane Demoiselle's design was by far the most advanced. The Boeings bought one, shipped it back the USA and began to make and sell copies - that was how the Boeing Company came to exist!

    Santos made many inventions and technical advances. One simple one was the "half ladder/ half stairs." - There was only a place for your right foot on steps 1, 3... and only for the left foot on steps 2,4... Etc. Thus, like a ladder you could climb nearly straight up; but like steps, there was full support below your entire foot.

    Summary: The Wrights had a better airplane than Santos' 14 Bis, but a terrible power to weight ratio motor, which they basically made. Santos had lots of money** and the best motors in the world. His had several times better HP to weight ratio. That is why he was the first to truly fly.

    *They were only about half the way down the rails and going slower than on other failed attempts that reached the ends of the rails with no separation from the rails. Quoting the same Wiki article:

    “The Wrights' early aircraft could sustain controlled flight, but always used some sort of assistance to become airborne, requiring a stiff headwind, or the use of launch rails. As such, none of the Wrights' early craft took off under their own power in calm wind from an ordinary ground surface as was achieved by the flights of the 14-bis. "

    The article, even though about Santos is quite biased pro-Wrights, IMHO. For example: It mentions that Brazil recognizes Dumont as first to fly and not fact that most all other nations do too - nor does it mention the fact that only the US recognizes the Wrights as first. (The Russians think their man was first also, at least they claimed so in the cold war era.)

    **Santo's father had large coffee plantation, even a railroad to take coffee to port. Not only that, but Santos during his prior Balloon flight era gave a ride to the king of Algeria, (I think it was), and despite their crash landing on the beach the king "saw the future" and generously funded Santos also - paid for a huge hanger for Balloons, not far from Paris.

    P.S. although I was responding to your claim that the pre- 1910 technology did not support mono-wing airplanes, I went into details about Santos as most Americans have never even heard of him. - He was a remarkable man, 100% committed to flying and had the money to be first in many aspects of flying. When he won prizes he gave the money away to workers and the poor.

    The Wrights were poor, sold their plane to the government and encouraged their applications in war - that disgusted Santos, who gave away even his patents. (Taken out only to make sure the ideas would be free to all.) Curtis, an motor cycle nut, who had better HP to weight motors than the Wrights joined force with the Wrights and that is how they made an airplane that could actually fly and sold it to the US Army. The army claimed that they had flown before the Wrights and did not want to pay for the Wright's technology. The army plane never flew either. They even had the wings upside down! (Flat surface on top, curved surface on the bottom! as they thought the wing should be like a rock skipping on smooth water. After they saw the Wrights had the curved side on top, they secretly turned their wings correct side up, and continued to claim their plane had flown. Fortunately, for the Wrights, in the financial struggles with the army, and old photo of the plane turned up clearly showing that the wing were originally wrong side up, and the Army dropped its "we were first" claims and bought planes from the Wrights; However, soon Boeing was soon selling copies of the Demoiselle and the Wrights went back to fixing bicycles and cars, etc.

    Again, the Wrights had the best airplane initially but lacked a motor with adequate HP to weight ratio for it to fly. One could credit them with the perfection of the scientific method applied to technology. –Many lab books filled with detailed wind tunnel measurements and calculations. I was once at the small Kitty Hawk museum, the only person there one cold winter day. After some discussion with the care taker on technical questions, he let me examine their lab books. They were very good scientists, understood everything well, especially how essential stable control of flight was, which Santos learned only by trial and error. If they had more money (or even joined forces with Curtis sooner) they surely would have been the first to fly.

    Santos did build dihedral into his first plane however and the Wrights did not think of that. (He had had a fast donkey pull large motor-less models along a long wire and saw the advantages of dihedral in these experiments. He knew that control was essential also from his ballooning years, but “canard solutions” which work well for long "cigar shapped" balloons are not stable for airplanes, which can rapidly turn.)
    Last edited by a moderator: Dec 19, 2008
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