Which is not true in the venturi. I think we are in violent agreement here. To be clear: to sustain a case in which the wind speed doubles due to use of a venturi, power cannot increase as the cube of the wind velocity, because there will be a reduction in molecules of air with that velocity, such that energy is conserved. The power can not change, therefore something else has to change in the wind power equation. And that's the mass component of the kinetic energy. Conventionally, in the wind power equation it's stated as density, so I picked that one. Density has to vary in order to hold power constant while velocity changes. That's all I'm saying Russ, I'm only adding to your earlier remark, not detracting from it in any way. Again, to be clear, we are speaking of a turbine placed inside a venturi. As I gather from looking at the photo the cross section of the venturi is just large enough to accomodate the prop. Therefore, the swept area under consideration is exactly the same as the swept area of the free stream turbine. Got that, Russ. As you'll see from looking at their data, most of it is in the 2-4 mph range. No gripes there. I didn't mean to put you through the hoops. I was explaining that in the wind power calculation, the statement "power increases as the cube of velocity" is unconditionally true for the free stream case, but in the venturi, it is conditioned upon supplying a vacuum to account for the extra energy gained. The alternative, I said, (paraphrasing) was that power shall remain constant, hence the density of fast moving air (across the same area, the area swept by the prop) must drop to conserve energy. I think the only confusion here is that I did not draw a diagram, label it and make it clear where I was. I was inside the venturi at this juncture. Here is where the number of moles of air must drop by the inverse of the gain from velocity boost. I only brought up perpetual motion in reference to the erroneous interpretation of their results inferred by the statement "600% power gain". I merely said that to claim any increase in power (energy) without an external source is to claim a common mistake made by some of the craftier perpetual motion advocates: they destroy energy, which is harder for naive people to spot than the ones who claim to create it. Obviously they are the same thing. Here, and only in the mind of the erroneous thinker, they destroy the energy (pressure x volume = energy, ideally) at the backside by (in their mind) creating a vacuum which is not there. This vacuum unburdens the conservation of energy that reduced the number of moles in the venturi, and now they do actually (in their mind) achieve 600% power increase since the number of moles returns to the number of moles at ambient while the velocity nearly doubles (cube root of 6 is 1.82). All of this, I said, comes to a screeching halt when the naive person who thinks that (not me) is confronted with the backpressure at the tail pipe where we find no vacuum, no energy was destroyed after all, and hence the whole idea peters out. There never was any benefit to using a venturi. However, I did add that it probably improves efficiency a little by reducing turbulence. Other than that, it can't do what they said it does (run faster in the venturi, produce more watts than outside in the free stream.) Again, since I think we are in violent agreement, pictures may help. I am referring to the purported claim that the power increased inside the venturi. It did not, other than (1) some incidental improvement in efficiency, such as reducing turbulence at the prop, or (2) some accidental (not by design) vacuum at the tail pipe. Nor did they publish electrical power measurements. The closest we have to wind power measurements are the anemometers which (I think; it looks like it must be so) were plotted without the turbine installed. Therefore, the perpetual motion inferred by their numbers must be inferred only as a matter of erroneous interpretation, namely, if the reader erroneously assumes that the 9:7 velocity improvement in their published data (see their figure 3 below) produced an actual power gain (in this case closer to 2:1), then it would lead that erroneous person to conclude that the venturi is tantamount to, if not the actual implementation of, a perpetual motion machine (over unity). Of course I would turn them over to you so you could take them out to the woodshed. Please Register or Log in to view the hidden image! Sorry for all the confusion. In my mind I actually thought I said what I said clearly. Evidently not. As a hint, though, keep in mind that I'm aware you know what you're talking about, so my intent is to supplement, not contradict you. They actually said "600% power gain" which is where all this hooplah started. I have to admit I don't understand why you are speaking of the data differently than I interpret it. I'll repost it here for your convenience. Look again at the day of the anomaly, when they got the 9:7 velocity gain. If you wish, you can tell me whether you think I misunderstand what it says. That might clear up any lingering confusion, since I get the feeling you didn't look at this too closely (not sure; just seems that way). And to be clear I understand that this is a comparison of shaft encoder ticks converted to wind velocity. In the alternative, it might be voltage across a load, translated to velocity by some other fancy footwook. But it looks like raw data which is why I suspect it's an encoder. I'll admit I have no idea. Once someone tells me I'll be happy to adjust my thinking accordingly. Here you go. Once again: the data highly erratic, no clear conclusions can be drawn from it. And again: See figure 3, day 5. Then look at day 1, and the periods where it's a toss. Please Register or Log in to view the hidden image!
I'm not following your objection to the basic setup here. If they are bringing the entire intake aperture energy - or even most of it - to a smaller, cheaper, more efficient and more durable turbine, that seems to be advantageous. Also, one can get a gain in turbine extracted power from the total by speeding up the airflow - not total net energy, but the fraction of turbine extracted energy, with the difference showing up in, say, a greater drop in speed or temperature of the eventually emitted air as compared with a propeller in the free stream (as you note, an air conditioner repairman's idea) or a back pressure loss of windspeed upstairs at the intake - and use that extra extracted energy to power extra electrons: why not? Fluid mechanics: One can spin a garden windmill much faster or against heavier loads with a nozzle on the hose, speeding up the water flow that strikes the blades; there are water pumps that work off of hydraulic ramming to lift irrigation water up from streams; the net energy books all balance, but extra work is done with the extra extracted fraction nevertheless.
You saw the quotes and sources. You tell me what the issue is and cite your source that explains otherwise. Let me say again: you guys are creating a conflict where none exists. We're not disagreeing that this device is a bad idea and doesn't do anything useful.
The problem is that that can't actually be done. The actual aperture is the area swept by the prop. Messing with the air outside of that area can't change anything. if you take a funnel with twice the area at the mouth and face it to the wind, such that it funnels all that wind down to the area of the prop, nothing will change. The prop will still develop the same amount of power. This is because the conservation of energy is working at every point on that disk where actual work is being done. As I understand you, it's the same reason as above. The only way the air can speed up is if the number of air molecules reduces in proportion such that the balance is exactly the same, that is, the total energy of the wind contained within one aperture can't vary. If it did conservation of energy would be violated. There are a few exceptions, like turbulence and efficiency changes that give different results, but they will always be reductions in that maximum amount. The big difference between opening a water valve and putting that water to work through a nozzle is that the water is pressurized to about 2 atmospheres. When it rushes out, it's rushing into a vacuum (1 atmosphere). In the wind, the pressure is about the same everywhere. This is more like being immersed in a water current than opening a valve with a nozzle attached. A better example would be to take a funnel or nozzle and hold it in a swiftly moving stream of water. You will feel the tug on it by the molecules that can't get through because there is no extra energy source to give them the boost they need. Instead they bounce back, a bunch of turbulence is caused, and all that excess energy that seemed to be for free, simply because the aperture doubled, goes to waste. The energy of the molecules that make it through has to be conserved too, although here the analogy breaks down. Since air is a gas, it's energy level is proportional to its pressure. That is, the pressure times the volume equals the energy. With water there is no analogy. It doesn't rush to fill a volume the way a gas does. It's always about 55 moles per liter. If you start with one liter of air, and then expand the container that's holding it, the molecules rush to fill the space and the pressure drops. If you try to do this with water, you'll expend a lot of energy, with virtually no change in the volume, and then at some point you'll begin to produce water vapor. So getting back to the question of putting a nozzle into the wind: I suggested earlier that a tuba could be faced into the wind, and if this invention worked, you could blow up balloons from the mouthpiece. The tuba player wouldn't be able to get a note out when facing the wind -- it would be like blowing into an air compressor. In that case the ratio of the tuba bell to the mouthpiece is much more than the venturi in this invention. In fact the bell is about the same aperture as the turbine, funneled down to about the diameter of a pencil. I did an estimate and came up with 1000:1 reduction in area. Since area of the aperture is directly proportional to wind power, that says that the poor dude with the tuba would be fighting with 1000 times the energy of the wind right there at the mouthpiece. Since the cube root of 1000 is 10, it says that in a 5 mph wind, his mouthpiece would be ripping out a pencil wide stream at 50 mph. Obviously that's not going to happen. Instead just about the same amount of air will be felt coming out through the mouthpiece, something closer to 5 mph than 50. And this is because there is no excess energy to produce a vacuum which is needed to drop the density and then, and only then, to increase the air velocity. Therein lies the rub. I really wish these guys had an actual solution, like anyone else I'm anxious to see some new cool cheap way to harness free energy. But on the other hand, if a second year science student could solve this on a homework problem, then it seems to me that the research money should be going to qualified people, not the air conditioning mechanics who convinced someone they knew how to speed up the air. It's not that big of a deal, I think they probably only blew a few million on it.
That sounds pretty good. Well, I think it is actually a bit more complicated than that. The difficulty here is that there is no initial static pressure (gauge), but extracted energy comes exclusively from a static pressure drop (times volume). Kinetic energy can't change across a low pressure axial fan/turbine because the diameter is the same on both sides and the velocity must therefore also be the same. So even in a normal wind turbine, some velocity pressure must first be converted to static pressure in the vicinity of the turbine before being dissipated at the turbine. Betz's law takes that into account and cancels-it out to give only the maximum extracted energy without discussing how it was actually extracted. In effect, a wind turbine has a nozzle and diffuser attached to it that you can't see. Kinda, but no. The "free stream turbine" is the area of the inlet, not the area of the cased turbine. That's the trick here: in the verbiage they appear to be comparing their cased turbine to the free stream of the same turbine, which is wrong. The proper comparison is between their cased turbine and the inlet area of their whole device, since that's the air being intercepted in each case: The energy they extract is less than the energy of the air intercepted by the inlet of their device. Agreed, and I really can't be sure if they know that or not. All I can really say is that the words sound like a perpetual motion claim, but their numbers do not show it. The "mistake" (if it is one) is comparing different swept/intercepted areas as if they were the same.
Right -- although I was only touching on the question of max. available wind power, as the rest seemed irrelevant to me since the reference turbine (the one on the pole) was the same make and model as the one in the venturi. Since they're only concerned with the difference between two performance curves, the rest of the details with efficiency didn't seem too important. BTW it's refreshing to hear you expand on your thoughts. You have a lot more going on that I had previously noticed. Right and I'm assuming those effects cancel in the difference calculation since they're the same for both units. Here you lost me. The plots are comparing the turbine on the pole to the turbine in the venturi. I have been using the term "free stream turbine" to mean the one on the pole. I'm saying the power of the wind it captures is measured across the same cross section as the area of the venturi itself, since it looks like the venturi-mounted turbine fits in there snugly. I say this because I recall that it had about a 1 m. prop diameter, and that appears to be the approx size of the venturi in the photo. In any case they obviously sweep the same area. Bingo. That was my original complaint when I said we can't figure out what these measurements are referred to. OK now we are on the same page for sure. BTW I think it's fine that they had a pole mounted turbine for comparison, but by providing only that, and not the diffuser data, there is a loss of calibration. All kinds of things might account for the erratic results they got. That's the important metric. Given that they are introducing a "cowling" (the venturi) they should expect some change in efficiency. I mentioned turbulence at the blade tips, normally reduced by a short duct. That alone should give cause to come up with a controlled test in which inlet velocity is measured. Actually, they did all of those kinds of measurements with the turbine removed from the venturi (I think; it sounded like that's what they did) so it seems odd that those data sets weren't all compiled together into one or two charts so the rest of the world could figure out what did or did not actually happen during testing. In other words, just leave the anemometers and pressure sensors in place and roll the data up into one composite of everything that was measured. Of course it's not over unity, and of course that's what most folks here are objecting to. That the claim smacks of an over unity claim. Here I think you're referring to the 600% claim which appears in the bar graph. I think you're saying that they must be comparing some 3rd turbine to turbine #1 (in the venturi)...??? And something like that crossed my mind when I first saw the bar graph, since the labeling is so vague. In any case the wind power ratio for the 9:7 velocity gain, which is their biggest performance data, only accounts for a (roughly) 2:1 gain in wind power . . .holding pressure constant and guessing, since they failed to give actual electrical power for an apples to apples comparison. Somewhere else I said that it almost appears that the wind tended to blow a little faster at their diffuser than it was blowing up on the pole, although on Day #1 the reverse is true. All the more reason for including their readings for the anemometers they placed in front of the diffuser. I would have clearly laid out the test arrangement with diagrams/photos and I would have talked about calibration, with some words about accuracy (what was being sampled and with what instrument) and I would have given all the pertinent data. Since the only thing that actually matters is electric power output, I would have simply plotted the two as a function of time, or even with the rest of the data so that a correlation could be seen between power output and measured speed. And there's no way I would publish an erratic data set without trying to characterize that anomalous spike at Day 5, the reversal on Day 1, and the times when data was about the same for both devices. In any case this is all kind of moot, but I still enjoy talking about it. What the world really needs is a good 5 cent turbine. That, a 5 cent solar cell, and a nickel battery. Please Register or Log in to view the hidden image!
FYI, I'm an HVAC engineer. I started in, but didn't do great in aerospace engineering, so I switched to mechanical. I deal with fan energy calculations every day and turbines are the other side of that coin. This problem is just a pinch outside what I do. Yes, but they prominently cite two numbers, but are less clear about what the numbers mean: -2x the free-stream velocity. -6x the power of the same turbine on a pole. The trick is that the 2x the velocity comes from a funnel with an opening that is more than 2x the area of the turbine: Saying you can generate 6x the power with the same turbine sounds impressive. Saying you can generate 25% less power with the same wind, notsomuch. Third? I can only see two unless you are saying one in two locations: 1. Turbine in a duct. 2. Same turbine in free stream. (1/6th as much power as in the duct) 3. 8x larger turbine (same capture area as the end of the funnel) in free stream, producing 6x as much power as 8x smaller turbine in the duct.
Right: So since no, no and no....no: -Due to the cost of the structure, the total device will cost more - not even including a mechanism to turn it, which hasn't been invented yet. -They actually claim it is less efficient. -More static structure and more drag means much larger forces and much more problematic durability.
You seem to be claiming that one cannot funnel wind and get a speed increase. I think I have experienced wind speed increases due to funneling, between buildings etc. The key would be the exact shape of the funnel - a tuba would be the wrong shape entirely, one would presume, but funneling shapes do seem to exist in the big world - ? If the inlet is larger than the turbine area, and facing the wind with the outlet side or down wind, a pressure drop would be available to boost speed without changing the number of molecules per unit volume through the blades. ? The pressure on a downwind or sidewind outlet area would be considerably less than the inlet pressure facing the wind. All windpowered turbines depend on a pressure drop downwind. Nevertheless, hydraulic ram water pumps do work - and waterturbine designs based on the principle exist: http://en.wikipedia.org/wiki/Hydraulic_ram I think you may be underestimating the cost of the far more sophisticated and design-constrained structures and mechanisms of propeller turbines. There seems to be no apparent need to turn anything, btw (if it works) - unlike the propeller designs, in which thousands of pounds of precision machinery, electrical connections and conductors, and close tolerance moving parts must be continually pivoted and aimed precisely while mounted on tall poles and spinning in all weather. Not the turbine itself, which is less constrained by the necessity of light weight and no maintenance needs and so forth. The drop in efficiency is for the operation of the whole thing. Static structures with few design constraints are intrinsically more robust and durable than moving ones with all kinds of issues re bracing, shape, etc.
You have the issue exactly backwards: conventional turbines are being built and installed, so there is nothing to estimate. It is this device that must be estimated. That's a bizarre claim considering that you were discussing the problems with turning the outlet duct earlier. Clearly, that is not a significant issue considering that it is routinely done. Yes: the whole thing is less efficient than a normal turbine of the same size and the whole thing will cost more than a normal turbine of the same size. So obviously it is a bad idea. 1. That is only true when comparing static and mobile structures of the same size. 2. Since the mechanism to rotate it hasn't been invented, you can't claim any particular fraction of the structure (or the whole structure) isn't moving. This is far from a trivial design constraint you are glossing over: Picture a thousand foot tall kangaroo hopping over its own tail.
Indeed I see that. I nominate you the site wind energy guru par excellence. I don't recall posts here that cover anything close to fluid mechanics so this is a good change of pace. Of course those are rolled up numbers but yes that's right. BTW I don't think it makes much difference if we call that 2x 1.8 (cube root of 6) since these were rough numbers anyway. Here I understand you mean 8x to 6x is a drop of 25%. My thoughts are that they were probably reading closer to 1.8x with the anemometers, so the 6x is OK but I also get your point, it's still not "100%". (In fact I think it was 630%, not 600%). One more thing: the unit they chose for this was 35% efficient (600W at 12.5 m/s, approx 1 m dia.). So that 6x (75% of max) represents a doubling and it's still way too high for the Betz limit. If I weren't so confused abut what they're actually telling us I might follow you better. #1 and #2 are the only ones I was thinking about; I don't follow what you mean in #3 --- are you referring to a model? Actually I can't figure that sentence out at all. The 8x refers to the calculated improvement with no turbine installed, just measuring the inlet vs venturi velocities with anemometers.. The 6x refers to electrical power improvement, and we have no idea what it's referred to. It sounds (from the labeling on the bar graph) like they are talking about some third turbine, almost as if they put together some performance data from typical efficiencies of larger turbines (maybe just guessing). Not sure. With your HVAC experience maybe you can appreciate my comments that this seems to me like an A/C repairman's idea. They have the idea in hand about how to increase air speed, but they seem lacking in the understanding of conservation of energy. You may have run into people like that, who are on the verge of understanding the physics, but lacking the full story, feel like something has been overlooked, that there's a big break for them to solve a real problem like this tries to do.
Then you should be able to recognize that the static and relatively simple structures necessary for this are likely to be relatively cheap in comparison - at least, there's no visible reason to think otherwise. If we look at towers built durable and cheap, like communication towers, they do not use windmill column designs - they use guy-wired cage constructions on minimal foundations, like this tunnel setup could use. No, I wasn't talking about turning anything, much less the entire turbine setup. The only related topic in my posts would be my comment that there seem to be a couple of obvious ways of aiming the outlet downwind or sidewind, unless for some reason nobody has posted they wouldn't work. I can't see much difficulty in rotating the whole thing anyway, especially compared with the problem of continually aiming a sky-mounted propeller turbine - which as you note is routine. Then it should be even less of a problem for this much simpler situation. (It is, of course, a significant source of expense and trouble for conventional turbines - routinely). So you assert, for reasons as yet invisible (I'm not yet sure what the term "same size" even refers to). There's no reason to rotate anything, that I can see. An outlet structure that looks just like the intake structure would allow a choice of outlet directions, for example. A flexible tube could be bent at need.
the bottom line is that if there is 100 watts of wind power available then you CAN NOT extract more than approximately 60 watts from it, and that's assuming 100% efficient rotor. i am unaware of ANY rotor that is 100% efficient and i believe that a rotor that has a certain efficiency at one windspeed will have a different efficiency at a different windspeed. my guess about all of this: their device captures wind over a large areaand funnels it to the turbine, they get their results. next they are comparing their results to the results of a turbine of the same swept area in free air. in other words they are comparing their cowled rotor to one standing in free air. you ARE NOT going to get any more power from the wind than what is available, and betz will reduce this to about 60%.
Yes, as I explained many posts ago: There is no energy extraction without (1) slowing the wind down to take KE from it NOR (2) with no flow thru the turbine. Thus, there is an optimum slowing of the wind that allows ~60% of its KE to be captured. As the energy in each Kg of the wind goes as the square of the wind speed, S. The optimum turbine exit speed, Se in terms of the undisturbed wind speed, Sw is found from (approximately): 0.6 = (Se/Sw)^2 Note that if Se= Sw /2 then that would remove 75% of the energy from the wind but is not possible as the flow thru the turbine is too slow. If Se = 0.7 Sw, then that is possible but removes only 49% of the KE in the wind as the turbine's exit speed to too fast. Note it is energy that is conserved, not power, which goes as the cube of wind speed. For example, you can "trickle charge" at low power a capacitor for 100 minutes, and then discharge it into a resistor during 6 seconds, for an average increase in power of 1000, but with some loss of energy. You can think of the venture as a "power transformer" but it will lose some energy. If the air speed thru it is twice the free air wind speed the power level is 8 times greater but energy is lost (to heat as air is compress prior to the venture in the decreasing radius section.)
When the high velocity air exits the venturi into the larger cross section, it expands; the pressure drops. This is a "necessary and sufficient" condition: the back side of the venturi *must* sustain a lower pressure. If not, then the low pressure "front" is held in check by the higher pressure front and nothing happens. That is, no gain in energy happens. At most, the same energy is captured that the turbine would have captured if no funnel were present. And indeed these people measured a 2x speed increase with anemometers. The trick is that they are like feathers. Just as the amount you feel consumes no appreciable power, similarly the anemometers consume no appreciable power. They will spin at the higher speed and everything will look great to our A/C repairman. When the turbine is inserted, it will even spin at the higher speed (assuming very low friction in the bushings). But the minute you put a full electrical load across the terminals, the turbine stalls (or slips) back to its nominal speed, back to however many RPMs it was spinning when on the pole in the same wind. And that's where that A/C guy can't figure out what's wrong because he didn't take the class that covered conservation of energy. For so many RPMs, the turbine produces so many watts of electrical power. You can spin it up to a higher speed with no load (no work is being done) but when you give it work to do it drops back to the slower speed, same RPMs as on the pole, same number of electrical watts, same energy over a given time period. Energy is conserved and all is well but the "wind amplifier" proves to be worthless. Actually the funnel is called a conical horn and the flared shape of the tuba is called an exponential horn. It has the property of matching the impedance of successive layers of air to themselves, if that makes any sense to you. Anyway, that's what gives them their ability to naturally amplify the sound of the notes being played. My thinking was that this would be superior to a funnel, but since it doesn't matter (no device can amplify energy by itself) it seemed like just as good an example as any. The thing is, we need to pull molecules of air out of the back of the funnel twice as fast as that wind will pull them out by itself. Therein lies the rub. The ideal gas law says PV = nRT. (Pressure x volume = the number of moles of air x the Universal Gas Constant x Temperature). As you see there pressure is neither a function of position nor of velocity. If it were, then you could blow up a balloon halfway, and starting at position x, walk in a straight line in the direction of the wind, and the balloon would expand as the air pressure dropped. At some point the balloon would burst. At some point you would completely run out of air molecules; you'd be in a perfect vacuum -- even though this was where all the air was going in the first place. And there could be no wind there at all. At some point before that all of your capillaries would explode and you'd run out of oxygen . . . like a spacewalk without a suit. Walking in the opposite direction, into the wind, as the pressure increased the balloon would shrink and shrink. At several atmospheres you would need to wear a diving suit. Running back and forth would cause the bends. It's this sort of idea that a pressure gradient must exist in order to suck air through the venturi which violates the basic laws I have in mind. So far I have been discussing the static pressure, which is due to the random motion of air molecules. The ensemble velocity - the amount they travel with same speed and direction as a group - causes the wind. Here there is another way to introduce local fluctuations in the static pressure simply by blocking their flow. It's the collision of these molecules onto a sail which transfers their kinetic energy to the sail, adding to the amount of force produced. These air molecules bounce back into the wind, and an excess number build up; hence the pressure is higher close to the sail than it is far away. This air is said to be in compression. It's denser. Meanwhile, on the back side of the sail, where the air molecules were blocked, there is a lack of them. They rush in from all directions only to be pushed along by the ensemble which is moving in the direction of the wind. A low pressure exists here; the air is less dense. So in order to develop this local fluctuation, an obstruction must be present. The problem is, it's difficult to create such an obstruction near the tail pipe of this contraption. As you see, there is none. This was what I meant when I said there was nothing about the outer body that suggests a shape, by design, which might induce the extra suction needed to pull twice as many air molecules out of the tail pipe as the wind will do by itself. It had occurred to me that a stationary wall placed there might induce the amount of suction needed. You could put an airplane wing there and cause an updraft that would help; things like that. But none of that is in place, which was what made no sense to me about the overall shape of the thing. There's nothing to suggest that the pressure drop behind the large intake (the mouth, which is a diffuser) is going to help add suction at the tail pipe, since they put the tail pipe so far away. In this case they are functioning like a simple sail. They don't get a boost in energy simply by adding a funnel or venturi in the water stream that's pushing the pumps and turbines. I was surprised to see that the contraption is not mounted on a turntable so that it could do the same thing. It would consume quite a bit of energy to move it, though, since it's not streamlined on the outside to reduce the buffeting of winds against the body. You could set up a rigid windmill, and it would work fine for prevailing winds that never change direction, but in all other cases it would lose power and stall when the wind changed more than about 45 deg. in either direction. If you look at the data I posted, they did have some shift in the wind direction. But it's not clear to me at all how wind direction affects the performance. The data just jumps around very erratically. They need to plot the index of correlation for power gain vs. wind speed. Without that, it actually makes no sense to me what the data is telling us. There are hard limits in efficiency for every machine. In fact it's impossible to build a machine that harnesses energy at 100% efficiency. You can get close, and because of this, a few posters here thought they have discovered perpetual motion machines(something that would at least keep moving even though it could produce no useful work.) Here (wind turbines) the losses are pretty bad. The Betz law predicts 59% as the top limit. That does not include losses in the windings, bearing friction, and losses due to turbulence. The type of turbine they selected for this test has a 35% efficiency rating overall; it cranks out 600W of electricity in a 27 mph wind moving across 1.6 sq meters. The reason I said they should try to improve on the turbine is that it may benefit from adding a short duct around the circle swept by the blades. That could be tested in a wind tunnel. But I think just about every conceivable design has been imagined, built and tested. There is a helical design which you might find appealing. It looks like a barber pole, so it receives wind from any direction without need for the extra pivoting machinery. And it's relatively compact. These are practical for underwater use, too, where they can convert water currents into electricity. The downside is that they don't have much surface area to capture the wind, so they're only good for low-power designs. If they could be made very cheaply you could at least put up a lot of them and get the same power as a medium size windmill. Other than safety (I'd hate to see a giant windmill fall over) what you're getting at is the enormous cost. Years ago I remember hearing about a delay in construction of wind farms due to a shortage of the giant ball bearings they use. There was only one supplier in the world who could make them (I have no idea how that's going now; haven't followed up on it). If you've ever seen a large turbine being transported on the highway they look almost like giant bridge spans. But it's a matter of scale, something bridge and building engineers are comfortable with. The fact that the designs are stable, that the kinks have been worked out at least reduces non-recurring costs. But back to your point. Yes, it would be great to have a way to capture wind energy at a fraction of the cost of a giant turbine. Here the constraint is in the actual energy content of the wind. It's relatively low on most days and then jumps as the cube of velocity when the winds pick up. That leaves it to design huge arms that can capture sufficient power when the wind speed is too mild to otherwise be of any use. All of the money and effort that went into the contraption we're talking about was based around a 600W generator. That's its performance at 27 mph. If you look at their plots it looks like they had maybe 4 mph average winds. Just guesstimating, let’s say that's a 1:7 reduction in wind speed: (1/7)[sup]3[/sup]=1/343; 600W/343 = 2W, a little less. Even if they got 6x as much that's only 12W, which is not quite enough to power two 7W night light bulbs. And the turbine alone costs between $600-$1200. That's what's so insane about wind energy. It takes a huge surface area to get any usable power. Except when the wind blows!
The windmills mounted in funnel areas between buildings or at the tops of walls etc do produce more power than those same windmills mounted in the free wind on top of the buildings. Conservation of energy does not in principle prevent this setup from working, because if it functions they are capturing the greater energy they need with the larger aperture. What is being created, at least in the ostensible setup as presented, is not an impossible boost in the total energy but an increase in the fraction of the energy that can be extracted to do work, funneling from a larger lower speed air mass to a smaller higher speed one. It's not a boosting of the total energy (pace their 600% claim, whatever that means) but a manipulation of the large amount of energy mostly unavailable in the large aperture due to lower speed of the free wind, so that it can be extracted and used to do work. They get a boost in the amount of work that can be done with the available energy, by using a larger and lower speed water mass to accelerate a smaller one. The inlet pipe is large, the delivery pipe smaller. Why? There's no advantage, if the thing works at all - the rigid inlet apertures face all directions, and the outlet is out of the wind altogether. If wind pressure on the outlet is a problem it could be bent, shielded, or multiple outlets set up for choice, but there's no reason at all to rotate the turbine. If it works, you don't need to do that expensive and touchy stuff you have to do with sky-mounted propellers. Or capture more of the low-wind energy at the same cost. That's if this thing does not work. It it works, the size of the turbine is not critical - the size of the apertures is. I went looking for the design I ran into a year or more ago, to see what they said - and found the same guys, actually, and the same lack of useful data or independent corroboration. They're local to me - a bit south of where I'm living - but secretive. Hmmmm.
Actually most medium sized (10-100kW) turbines do use guy-wired towers. They are by far the most common structures for medium size wind turbines. However, such designs only work well when the load is at a single point. They do great when the force on the tower is centered near the guy wires; the guy wires then resist in tension, which is the direction they are strongest. (Actually the only direction they have any strength.) A wind turbine presents such a point load since it is free to pivot. They would not do as well with a structure that introduced yaw loads of the sort you would get with a large lateral structure. While there would not be much difficulty, there would be some. You could either rotate the structure AND the guy wires (requiring a platform hundreds of feet across, both free to rotate and resistant to lifting loads from the guy wires) or build a solid structure and rotate it on a solid base. Doable but certainly more expensive than your average tilt-up tower. True - but then the turbine would have to be built to deal with the turbulence you would get, and would also be able to use winds coming from fewer directions. Again, it could work, but would result in higher costs per kilowatt-hour.
some infro for bird lovers that are anti-wind power: Please Register or Log in to view the hidden image! This is because birds, especially those that soar with no wing flapping are fantastic sensor of small disturbace in the wind, and wind machines make great disturbances both up and down wind. Any bird a wind machine kills, had serious genetic defects in this sensory system - I.e. wind machine only refine / improve the "gene pool" of birds.
Though the lethality of wind turbines is exaggerated, it isn't true that competent birds in flight can be expected to sense and avoid the blades - certainly nothing that cannot avoid the smaller, slower, and much more turbulence generating approach of a car can avoid a turbine blade, and birds migrating at night are protected only by choice of route, choice of height, or lottery luck. Don't build the things across the concentration bands of low level night migration routes, or near major breeding populations of large soaring or high flying birds, or at critical places important for endangered species, might be the rules. It's a factor, is all - minimized mostly because good sites for wind power are not usually congenial places for flocks of birds to hang out tens of meters in the air. That graph up there underestimates the role of cats, btw, according to data released this past month - the older estimates have been doubled or tripled, depending on location. Just to clarify - the rotation need only involve the "whole thing" of the outlet structure - somebody objected that the thing in the picture would be pointing up wind often, reducing or preventing outflow of slowed air, and I jsut wanted to note that there seems to be little to prevent it simply being revolved or bent to a right angle with any wind at its level, creating a pressure drop across the outlet mouth. The tower would be fixed, of course - one of its advantages.
