Salient White Elephant

March 29, 2009

Eye of the Cat

From an aerodynamic perspective, the ideal vertical axis wind turbine rotor is the “H Rotor”:

H Rotor

Unfortunately, from a mechanical point of view, the H Rotor is terrible. This is so because as its blades bow out, seeking the troposkein shape, a tremendous load is applied to the horizontal beams that support the blades. This load is in exactly the direction that the beams are least able to support (tending to pull the ends of the beams together).

Mother Nature Doesn't Always Care What We Want

Now you know why the only H Rotors you see on YouTube are on small turbines rather than on utility scale machines. The small H Rotor is essentially a brute force solution to the problem. That is, if you’re only interested in small machines, then you can just make the stiffness of the blades and blade supports large enough to resist the tendency to assume a troposkein shape. Don’t get me wrong… I think the H Rotor is a good idea for small machines that will run the meter backwards at somebody’s home. But I just want to point out the irony in this approach, for if you go in the opposite direction, the problem goes away! To see this, simply imagine an H Rotor with a diameter of 10 miles. Now the velocity of the rotor blades is essentially linear, and there is no centrifugal force to bow the blades! (A little thought will reveal that the centrifugal force disappears because the airfoil velocity is always the same, regardless of the rotor diameter. This is true because the blade velocity is determined by wind speed and by the desired tip speed ratio. So if the wind speed is 20 mph and the desired tip speed ratio is 6, then the airfoil will travel at 120 mph regardless of the rotor diameter.) Of course, the aerodynamic forces also cause the blades to bend. In any case, it would be nice if there were an alternative technique, and there is! It is the mysterious and enchanting Eye of the Cat, and it eliminates the tendency of the blades to bow, whether this tendency is caused by aerodynamic forces or by centrifugal forces!

Eye of the Cat Darrieus

The aerodynamics of this rotor are close to ideal because we can select any blade shape that has the symmetrical force-balancing properties depicted above. (Actually the centrifugal force on the outer blade is greater than the centrifugal force on the inner blade, but they are approximately equal. If necessary, weight can be added to the inner blade to balance the opposing forces.)

I’m not sure what to think of the Cat’s Eye Turbine. It seems to me that it will work as described, but it does have some strange properties. For one thing, it is unstable. To see this, imagine the blades are supported by cables instead of beams. We have carefully added weight to the inner blades so that the vertical forces tending to increase the distance between the ends of the cables exactly balance the vertical forces that draw them together. However, any perturbation that slightly increases blade curvature also increases the centrifugal force on the outer blades, and decreases the centrifugal force on the inner blades. In this case, if the blades are sufficiently flexible, they will subsequently increase in curvature until the outer blade and the supporting cables form an approximately troposkein shape, while the inner blade mirrors the shape of the outer blade in the opposite direction. Furthermore, any perturbation that slightly straightens the blades will also increase the centrifugal force on the inner blades, and decrease the centrifugal force on the outer blades. In this case, both blades will eventually become perfectly straight, and then both blades will bow all the way out together until the whole structure, cable and blades, assumes a troposkein shape.

But on the positive side, consider how even the aerodynamic forces seem to resolve into approximately equal and opposite vertical forces on the ends of the supporting beams! Meow!!

It guess the feasibility of this machine boils down to whether the beams that support the blades can have stiffness sufficient for keeping the rotor from becoming unstable, and also whether the designers can put the rotor’s natural frequencies into an appropriate range.

Rotating Guy Wire Variation

Cat's Eye Darrieus, Rotating Guy Wire Variation

Traditionally Guyed Variation

Cat's Eye Darrieus, Traditionally Guyed Variation

Non-Vertical Axis Applications

The Eye of the Cat can also be applied to the Direct Drive Linear Turbine With Yawing Oblong Track, Radially Displaced HAWT Rotor, the HAWT With No Shaft.

March 28, 2009

Wind Turbine With Flow Accelerator Beneath Rotor

Filed under: Horizontal Axis Wind Turbine (HAWT) — Salient White Elephant @ 7:20 am

Wind Turbine With Dirt Mound Flow AcceleratorWind Turbine With Flow Accelerator Skirt

March 27, 2009

Wind Turbine With Flow Accelerating Shroud

Everyone knows that a smaller wind turbine rotor may be used if a shroud accelerates flow in its direction. Most people who know much about the design of utility scale wind turbines don’t take this idea seriously, and I confess I never took it seriously either. It just seems like an idea that cannot be applied to a large wind machine. But here are some ideas for light-weight shrouds that can be easily retracted during storm wind conditions:

Wind Turbine With Flow Accelerating Shroud

The idea is to provide a shroud that is made from some flexible material (nylon or whatever… I don’t know anything about materials). The shroud is shaped like a giant cone with its large end opening in the downwind direction (colored aqua in the diagram). But the cone is flexible… how will it be supported? It is supported by attaching its large opening to the small opening of another conically shaped shroud (colored purple in the diagram). The large end of the purple shroud opens in the upwind direction. The two upwind openings of these shrouds are each supported by a rigid ring – sort of like bending a couple of giant coat hangers into circles:

Downwind View Wind Turbine With Flow Accelerating Shroud

In order to help the shrouds hold their proper shapes, some kind of minimally designed light-weight rigid supports may be added:

light-weight ribs may be sewn into fabric of shroud to help maintain proper shape

Now we get to the second big problem with shrouds – their terrible storm wind drag profile. But since the shrouds are nothing but flexible fabric, they can easily be designed to fold into a shape that has a low drag profile! In fact, if the shrouds were well designed, it seems like maybe this machine would have even a much improved storm wind drag profile as compared with a traditional design with the same rated power output.

Giant Spoked Annular Wheel Variation

Here’s an interesting variation on this idea. This shroud sits on the ground or on a small post with bearings for yawing:

Wind Turbine With Spoked Annular Shroud, Downwind View

One interesting feature of this idea is that it makes use of all of the energy in the wind all the way down to the ground!

Wind Turbine With Spoked Annular Shroud, Side View

The following diagram shows how the shroud looks like a doughnut sliced in half (the doughnut slice and the cross section slice are in different planes):

Cross Section of Side View of Fabric Part of Shroud

The next diagram shows how the shroud may be deployed or retracted much like opening and closing drapes:

Wind Turbine With Spoked Flow Accelerating Shroud, Deploying the Shroud

Partial Cross Section of How Shroud is Deployed or Retracted Like Opening and Closing Drapes

Of course, another way to reduce the storm wind drag profile is to just lay the whole turbine down on the ground. Can’t get a much better drag profile than that!

Linear Turbine Variation

Here’s a variation that resembles the Direct Drive Linear Turbine With Yawing Oblong Track:

Shrouded Linear Turbine With Elongated Oblong Track

Direct Drive Linear Turbine With Yawing Oblong Track

Direct Drive Linear Turbine With Yawing Oblong Track

Direct Drive Linear Turbine With Yawing Oblong Track, Close Up View of Blade to Blade Guide Interface

Although the direct drive apparatus isn’t shown in the diagrams, a written explanation should suffice. Permanent magnets are attached to the blade supporting structure that is at each end of the airfoils. The airfoils drive these magnets at a speed that is analogous to the “tip speed” of a more traditional wind turbine. Generator windings are built into the blade guides (aqua colored components in diagram above). Instead of embedding windings into the entire length of the blade guides, windings are separated somewhat. Blades speed up slightly while traversing the distance between windings.

Direct Drive Linear Turbine With Yawing Oblong Track, Aerial View

The blade inverting sections of the track permit the use of asymmetrical, pitched airfoils. (Asymmetrical, pitched airfoils deliver better aerodynamic performance than zero-pitch, symmetrical airfoils. For an explanation of the “helical airfoil inverting section” of the track, see my earlier post: 20 Megawatt Direct Drive Darrieus.)

I wonder if the blade guides can be flexible? If so, the flexibility may provide a number of benefits. For one thing a flexible guide might be cheaper, lighter in weight, and easier to build. For another, it may help to absorb abruptly changing loads due to (for example) wind gusts. It might be interesting to explore the possibility of a blade guide which is flexible enough to resemble, to a degree, a hanging cable, and yet which is still rigid enough to accurately maintain the tight mechanical tolerances that would be required for the direct drive generator components contained within it:

Can Blade Guides Be Flexible?

Two Hanging Cables Variation

Airfoil Suspended Between Two Cables (Drive System Omitted)

(If you haven’t yet read about why you might want to invert the blade, click here.)

Airfoil Suspended Between Two Cables

Close Up of Drive System for Airfoil Suspended Between Two Cables

It might be interesting to explore how the Eye of the Cat Rotor Blades would perform when hanging from two cables. Although there’s no centrifugal forces to balance, remember that the Cat’s Eye Rotor also balances aerodynamic forces. In this case, think about what happens if the blades are longer than the separation distance of the cables (including slack… so that they tend to keep the cables pushed apart).

Single Hanging Cable Variation

In this variation, sensors detect when two airfoils get too close to each other. In this case, the direct drive generator coils for the leading airfoil are switched off until it reaches an acceptable distance from the airfoil immediately behind it.

View Looking Down Structural Cable Cable Hanging Between Towers

View Looking Down Structural Cable, Moving and Stationary Parts, Cable Hanging Between Towers

View Looking Down Structural Cable, Big Picture, Cable Hanging Between Towers

Downwind View, Airfoil Entering Helical Blade Inverter

Aerial View, Airfoil Entering Helical Blade Inverter

March 26, 2009

Unmanned Aerial Vehicle (UAV) Turbine

Unmanned Aerial Vehicle (UAV) Turbine

One of the most significant features of the UAV Turbine is that its tethering system connects the airborne device to either two tracks, or else to one track and a ground anchor situated at the axis of rotation. Other airborne wind machines tether the airborne device with only a single cable. In this case, the airborne device is poorly positioned to make the transition from its upwind arc to its downwind arc, and vice versa. Of course, tethering with two cables isn’t very appealing. But one of these cables can be eliminated if an oblong track is used. For more on this, see Direct Drive Linear Turbine With Yawing Oblong Track.

Using small, light-weight tubes that are shaped like a symmetrical airfoil to tether the airborne device allows them to make a small contribution to output power. Otherwise the only contribution they make is drag.

The UAV Turbine can use kites instead of airplanes. Or it can use floating devices, such as the airfoils described in the Helium VAWT post.

March 25, 2009

Displaceable Guy Wires

A number of Salient White Elephant blog posts describe guy wire, tube, or lattice supported towers in which the supporting structures can be moved to make way for a yawing rotor or for other yawing components. Here’s an idea for realizing this functionality:

Displaceable Guy WiresTower With Three Guy-Wire-Like Displaceable Support Tubes

Planar Rotor

It seems to me that there is only one path for rotor blades that delivers the ideal aerodynamic performance:

Aerodynamically Ideal Oblong Rotor Blade Path

The long dimension of this path can be horizontal, vertical, or it can be anything in between. In other words, as long as the long dimension of this path is at a right angle to the approaching wind, then the path is ideal. (Of course, another way of realizing this path is to use a reciprocating design in which the airfoil exactly retraces its path when it changes directions.) Here’s one way to implement an ideal path:

Downwind View of Planar Rotor

Side View of Cutaway of One End of TrackAerial View of One End of Airfoil Track

Here’s another way to realize an ideal path: Direct Drive Linear Turbine with Yawing Oblong Track.

March 24, 2009

HAWT With No Shaft

HAWT With No Shaft

HAWT With No Shaft, Side View

HAWT With No Shaft

What if the blade is longer than the diameter of its supporting frame? In this case, the blade tends to act like a spring, pushing against the frame so that it deforms slightly into an oval shape. When the blade spins, centrifugal force makes the blade push even harder against the frame. But the aerodynamic force tends to bow the blade, giving it tend to pull on the frame and shorten its diameter. Perhaps these two opposing tendencies could approximately balance each other, thereby reducing loads on the frame. Bowing the blade has another interesting effect – it tends to make the blade tips orthogonal to local flow:

Tips of Bowed Blade More Orthogonal to Local Flow

The HAWT With No Shaft is supported by 5 guy wires. When the rotor yaws, it makes contact with only one guy wire at a time. When it comes to a point at which is about to make contact with a guy wire, the guy wire is moved out of the way. For ideas on how to move guy wires out of the way see my earlier blog post Scalable Tower for Very Large Wind Turbine. Here’s a combination of the HAWT With No Shaft and the Highly Scalable Horizontal Axis Wind Turbine:

HAWT With No Shaft, Highly Scalable Wind Turbine Variation

Radially Displaced HAWT Rotor

Radially Displaced HAWT Rotor, Side View

Radially Displaced HAWT Rotor, Downwind View

Only the airfoils rotate in this machine. The flow accelerators are supported in the manner of a wheel with spokes. Each end of each airfoil is attached to a cable that moves like a rotating ring inside of its flow accelerating shroud. The cables drive the generators. (Generators not shown in diagram.) Alternatively, the flow accelerating shrouds can house direct drive generators in the manner described in an earlier post entitled Flow Accelerating Ring Generator for Horizontal Axis Wind Turbine.

It might be worth considering a combination of this idea and the one described in Highly Scalable Horizontal Axis Wind Turbine.

March 23, 2009

Direct Drive System for Horizontal Axis Wind Turbine

Direct Drive System for Horizontal Axis Wind Turbine, Mechanism That Catches Blade Tip

Direct Drive System for Horizontal Axis Wind Turbine

The diagrams are not very well done, and certainly not sufficiently detailed. But basically what happens is that a blade catching mechanism follows the blade that it catches through the arc shaped guide. After the blade moves past the end of the guide, the blade catching mechanism begins its return trip back to the beginning of the arc shaped guide. The blade catching mechanism will arrive at the beginning of the arc just in time to catch its blade as it comes back around. All three of the blade catching mechanisms behave this way, and they are synchronized in order to catch each blade with little mechanical shock on impact (i.e. a blade catching mechanism is moving at the same speed as the blade at the moment it makes contact with the blade).

The mechanical system that incorporates the three blade catching mechanisms also drives the (off-the-shelf) generator.

Wobbly Wind Speed and Direction Sensor

Filed under: Wind Turbine Auxilliary Devices — Tags: , , , , — Salient White Elephant @ 5:15 pm

Wobbly Wind Speed and Direction SensorImagine a typical three-cup anemometer. One cup is smaller than the other two, and the other two are the same size. In this case, the rotation speed will vary in a roughly sinusoidal fashion. The speed will be low when the small cup opens up towards the on-coming wind. If, from this position, you rotate the cups 180 degrees, the open end of the small cup will now be in the downwind direction. This will be the position at which the rotation speed is at a maximum. The angular position of the rotating part of the sensor is sampled a number of times per rev. A Fourier Transform is employed to determine the average rotation speed, as well as the phase of the sinusoid relative to some known angular position of the cups. The average rotation speed is proportional to wind speed, and the phase shift reveals its direction. Alternatively,  the amplitude of the sinusoidal variation in rotation speed may be used to calculate the wind speed.

Actuated Variation

In this variation, a small motor drives a rotating paddle at constant rotation speed. Now the instantaneous power consumed by the motor is sinusoidal. The wind speed is a function of the amplitude of the sinusoidal instantaneous power flowing into or out of the motor, and the wind direction is determined from the phase of the sinusoid. Alternatively, the sensor can resemble a miniature Darrieus rotor, with wind speed and direction calculated using similar Fourier techniques.

March 20, 2009

Wheel in the Sky

This is a horizontal axis machine. Imagine a giant wheel with six spokes – three upwind and three downwind:

Spoked Wheel

The spokes are airfoils. The rim simultaneously provides three functions – it is a vortex spoiler, flow accelerator, and it is an aerodynamic shroud that contains the parts of a giant ring generator. Just as the spokes of a wheel rotate with the wheel, the aerodynamic rim rotates with the turbine blades. Generator windings are embedded in the rim along its entire circumference. The permanent magnets are embedded in a component that is shaped like a 60 degree arc. (I’m not sure how many radians the arc needs to sweep. I’m just guessing it might be in the neighborhood of 60 degrees.) When the turbine isn’t turning, the 60 degree arc rests on top of the ring that carries the windings in the 6 o’clock position. The arc has wheels beneath it that regulate the small gap between the magnets and the surface of the ring that carries the windings:

Ring Generator, Wheel in the Sky

Now when the turbine rotor begins to turn, the arc with its magnets will turn as well. However, it won’t turn very far before the gravity generated counter-moment will balance the force that tends to drag it along with the (generator) rotor. At this point the machine will begin to produce electricity.

Precision Air Gap Variation

This variation employs segmented arcs that are connected end-to-end. This allows the air gap to be independently and accurately regulated for each stator segment:

Wheel in the Sky Ring Generator, Precision Air Gap Variation

Advantages and Disadvantages of Wheel in the Sky

It is unfortunate that the outer surface of the aerodynamic ring must travel at blade tip velocity. This will certainly generate a great deal of turbulence. But consider the benefits:

  • diminished blade tip vortices,
  • accelerated flow near blade tips,
  • airfoils supported at both ends (lighter, stronger airfoils),
  • low noise (six blades mean diminished rotor rpm),
  • precision direct drive generator,
  • extremely large diameter ring generator (high speed generator rotor),
  • zero torque main rotor shaft.

That’s an impressive list of benefits. Will these advantages outweigh the aerodynamic losses of the rotating rim?

By the way, it might be a good idea to combine the Wheel in the Sky and the Highly Scalable Turbine.

Internally Actuated Bipolar Airfoil

Filed under: Wind Turbine Airfoil — Tags: , , , — Salient White Elephant @ 7:21 am

Internally Actuated Bipolar Airfoil

March 19, 2009

Flow Multiplying Anti-Vortex Drive

This machine has a blade tip that simultaneously performs three functions. It is a kind of elongated, arc-shaped vortex spoiler, and it is pitched relative to the oncoming wind so that it also accelerates flow through the rotor disk. It’s third and final function is to streamline and support the permanent magnets of a direct drive ring generator:

Flow Multiplying Anti-Vortex Drive

Flow Multiplying Anti-Vortex Drive

How can the (generator) rotor pass through the stator without hitting it and still maintain the close tolerances that are required? I don’t know, but perhaps some sort of guide system can be designed that routes it through the stator. The following diagram gives the general idea. It shows a wheel approaching a guide. The wheel is not necessarily aligned with the guide, but the funnel-like shape of the guide causes it to make any necessary adjustments in position.

router

One disadvantage of the Flow Multiplying Anti-Vortex Drive is that the structure housing the stator coils must yaw with the nacelle and rotor. However, if the drive idea is used together with the Highly Scalable HAWT idea, then the stator coils may remain fixed, and do not need to yaw with the rotor blades.

Helium VAWT

Helium H-Rotor

Have you ever seen those things that look like a cross between a parachute and a hang glider? I’ve seen people jump off a mountain with these things and fly around for hours. Though I observed them from a great distance, they appeared to move at an impossibly low velocity. I was amazed that they didn’t just fall out of the sky. I’ve heard low speed aerodynamics is a unique and somewhat black art. I don’t know if this is an accurate characterization or not, as I know nothing about this practice. I guess I’m just thinking maybe there’s an application for a low speed wind turbine. Perhaps powering a small remote installation of some kind. In this case, maybe a machine like the one depicted above would be appropriate. It would also be interesting to think about an application where a wind turbine would be over the heads of a lot of people. In this case the idea of having a thousand pounds of rotating metal and fiberglass overhead might make some people uncomfortable. But I find it hard to believe an overhead balloon would pose much danger.

March 18, 2009

Flow Accelerating Ring Generator for Horizontal Axis Wind Turbine

Flow accelerators don’t seem appropriate for utility scale horizontal axis machines. It’s probably much easier to just make the blades longer, especially given that blades will probably generate far less drag in storm winds. But what if the real purpose of the flow accelerator is to hide a ring generator? In this case, the size of the flow accelerator is the minimum required to shroud and contain the generator. Any increase in power output due to accelerated flow is “icing on the cake”, since otherwise the accelerator is designed to have minimum storm wind drag profile.

Flow Accelerating Ring Generator for Horizontal Axis Wind Turbine
Though not shown in the diagrams, the end of the airfoil goes through a slot in the accelerator, so that the blade tip is actually inside the accelerator. Alternatively, some kind of metal extension can extend from the tip of the airfoil through the slot in the accelerator. The part of the blade that is inside the accelerator is attached to an arc shaped housing for the permanent magnets of the ring generator.

Given modern wind machines are approaching a scale that leaves even the engineers pointing and goggling, it makes little sense to keep taking the torque off the wrong end of the airfoil.

There are two major challenges to this design. The first is how to accommodate for bending and vibration of the end of the rotor blade. The second is how to maintain close mechanical tolerances in such a large ring generator. I have not given thought to the specifics of how these problems might be solved, but I do have a philosophical approach I’d like to share with you. When a pilot turns the steering wheel of his state of the art modern airplane, the ailerons are electronically actuated. As expected, electric motors and microelectronics realize the actuating system. This system has a very cool trick for moving the ailerons to just the right angle. The trick does not involve impossibly accurate and brittle (in the sense of non-robust) design and manufacturing processes. The electric motors are not precision Swiss watches. Instead, a feedback loop is employed. The challenge in designing such a system mostly involves control theory – a well understood science. I am suggesting that the successful implementation of a “mega-ring generator” may possibly employ the same approach.

Flying Rotor

Flying Rotor, Rotor Stationary

Flying Rotor, Rotor Spinning and Producing Power

Centrifugally Actuated Variation

When the blade depicted below begins to spin, centrifugal force will lift it up:

Centrifugally Actuated Flying Rotor

Articulated Variation

Flying Rotor, Articulated Variation

March 17, 2009

Darrieus with Inverting Asymmetric Airfoil

One disadvantage of the traditional Darrieus Turbine is that it requires symmetrical airfoils of zero pitch. This is unfortunate, since a pitched asymmetric airfoil has much better aerodynamic characteristics. Because a given side of the Darrieus airfoil must serve as the high pressure side for half a rotor turn, and then as the low pressure side for the other half turn, Darrieus machines have not been able to take advantage of the superior performance of the pitched asymmetric airfoil.

This post describes a technique for inverting the airfoils twice per rev. This permits the Darrieus to employ pitched asymmetric airfoils:

Blade Inverting Darrieus Has Asymmetrical Airfoils

Darrieus with Constant Non-Zero Pitch Inverting Asymmetric Airfoil (Side View)

I believe in three bladed Darrieus machines, but it’s usually easier to use two bladed machines in diagrams and explanations, and that is what I have done here. As the two-bladed Darrieus approaches the rotational angle at which it produces no power, the airfoils may rotate freely. This doesn’t matter because they aren’t torquing the rotor anyway. As the rotor enters the other half of its power producing arc, the net wind velocity vector shifts so that it is no longer parallel to the airfoil’s velocity vector. Now the airfoil is mechanically stable, but unless its high pressure side is upwind and its low pressure side is downwind, it is aerodynamically unstable. If unstable, it will flip over so that the polarity of the airfoil is appropriate for the given power producing arc.

The embodiment depicted in the above diagrams is only one of many variations. Basically, it boils down to this:

  • Each airfoil is able to rotate about about a horizontal axis tangent to its circular path of motion. (If the airfoil is pitched, then its chord will not be parallel to its axis of rotation. In this case, the chord will sweep out the surface of a cone if the airfoil is rotated 360 degrees. However, the axis of rotation is still tangent to its circular path of motion.)
  • The mass of each airfoil is balanced with respect to its axis of rotation. (“Axis of rotation” here means the airfoil axis – not the rotor axis.) Because the airfoil is balanced, centrifugal force will not cause it to rotate.
  • The airfoil is aerodynamically stable when the high pressure side of the airfoil is upwind and the low pressure side is downwind. The airfoil is unstable when oriented with the opposite polarity. In this case, aerodynamic forces will rotate the airfoil, causing it to flip to the other side.

Actuated Variation

A similar approach would have the controller actuate the airfoils. In this case, the controller has a wind vane just like a horizontal axis machine, and uses this information to determine when to flip the airfoils.

Unbalanced Variation

Note that if the circular path of the VAWT blade has a large diameter, centrifugal forces are greatly diminished. In this case it may not be necessary to counterbalance the inverting blade.

March 15, 2009

20 Megawatt Direct Drive Darrieus

No, 20 MW is not a typo… this post describes a Darrieus Wind Turbine configuration that to me seems almost infinitely scalable. I chose 20 MW out of a hat because I felt it’s a good jazzy way to communicate the immensely scalable nature of this machine.

Actually, this post describes two interesting ideas – a concept for designing a highly Scalable Darrieus Wind Turbine, and a direct drive concept for eliminating the turbine’s gearbox. And by the way, the direct drive concept will work on horizontal axis wind machines as well.

I’m not a mechanical engineer, so many of the diagrams presented here are purposely naive. I’m taking this approach because I feel that the most important objective of this blog post is to communicate the significant and novel aspects of these two ideas – the scalable turbine and its direct drive system. If these ideas prove viable, I hope that some talented scientists and engineers will find the right mechanisms, configurations, and designs for reliably implementing these concepts.

The Scalable Darrieus Wind Turbine

The basic idea is to provide an improved and more scalable means for guiding and stabilizing the airfoils of a vertical axis wind turbine, and also for carrying the airfoil loads. This is accomplished with a stationary circular track that is suspended in mid-air. The track is supported by a number of towers arranged in a circular fashion. The following diagram illustrates these features. (In the interest of clarity, the diagram has quite a few simplifications. For example, only two towers are depicted. An actual machine would have at least three towers. A large diameter machine will have as many towers as are necessary for supporting the track and its loads. Furthermore, only two circular tracks are shown. A very tall machine will have as many circular tracks as are required to stabilize and support the airfoils, and to support the direct drive generators that I will describe momentarily.)

20 MW Direct Drive Darrieus Wind Turbine

Here are two of the naive diagrams I promised you earlier. These diagrams describe the general idea for implementing the interface between the airfoils and the suspended circular track. First, an aerial view:

100 Megawatt Direct Drive Darrieus, Mechanism For Maintaining Airfoil Vertical Stability

And here’s a side view:

100 Megawatt Direct Drive Darrieus, Airfoil Engaging Stationary Ring

The circular track cross-section doesn’t look very streamlined, does it? No matter… we can easily come up with a shape that minimizes the turbulence generated by the track. The structure that supports the wheels (colored purple in the diagrams above) will also be streamlined, and the shape of the circular track will be modified in order to shield, to the greatest extent possible, the wheel supporting structure from contact with the wind that flows through the rotor. It is also very important to notice that the negative aerodynamic characteristics of the track, the towers, and any auxiliary devices that are attached to the airfoils (like the wheels and their supporting structure) are nothing to be concerned about. This is so because it is easy to “drown out” these negative effects with scale. For example, adding more towers certainly increases the turbulence in the wind flowing through the rotor, but this isn’t a problem because each tower added permits the scale to be increased by a very large fraction. Thus, the added energy capture from the increase in scale more than makes up for the increase in aerodynamic interference.

If you’re like me, you just don’t feel right sticking auxiliary mechanical devices on the high speed part of an airfoil.  Here’s a couple of alternative implementations that get around this problem. Neither of these implementations would contribute significant aerodynamic drag, though mechanical friction would still be present. These implementations employ a great many wheels that are attached to the circular track, and that engage the airfoil one after another as it makes its way around the track:

Airfoil Engaging Stationary Ring

Here’s a modification of the apparatus above that minimizes airfoil bouncing:

Multiple Tiers of Wheels Reduce Airfoil Bouncing

And here’s the second alternative:

Airfoil Engaging Stationary Ring

One of the problems that the wind industry is currently struggling with is the growing size and weight of wind turbine components. In some cases the components grow to a size that can’t be transported to the wind farm construction site. In other cases the components are so heavy, and are suspended at such great height, there are no cranes available that can handle the job. For these reasons, I’m thinking that a very large Scalable Darrieus Turbine may have a number of smaller, light-weight blades. Selecting a multiplicity of small airfoils instead of two or three big ones also makes for a quiet machine, not to mention a safer one. And more airfoils reduce the fluctuations in thrust and output power that so notoriously plagued the traditional two-bladed Darrieus. If a multiplicity of smaller airfoils is selected, perhaps the blades could be assembled from sections at the wind farm construction site:

Blades Assembled From Sections

I once had a Bergey 10 kW blade. It was fascinating. It was made with a low cost fiberglass extrusion process. It was very strong, yet flexible. I’m wondering if a very long blade could be manufactured by connecting many of these sections end to end.

It may be necessary to provide the Scalable Darrieus with a means for neutralizing the tendency of the blades to outrun or lag behind one another. There are many ways of doing this, and I don’t think it will be very difficult to implement this functionality. One method would employ a giant small diameter circular tube that is very light in weight. This tube would connect the wheel supporting structure of the airfoils one to another. Here’s the general idea:

20 megawatt Direct Drive Darrieus Blade Synchronization

Though not shown in the diagram, the synchronizing ring would rotate inside of the circular track. In this case, the circular track acts as an aerodynamic shroud that shields the rotating ring from contact with the wind that flows through the rotor. This minimizes drag, and it minimizes the turbulence generated by the ring.

An alternative way to synchronize the blades replaces the circular tube with a cable. This cable is also shrouded by the blade guiding track. I don’t have time to explain it right now, but I’ll add this and more to this blog post in a few days. (And in addition to the cable, there are still other alternatives for synchronizing the blades.)

Variations on the Scalable Darrieus Theme

I don’t even know where to start. I’ll bet you’ve already thought of a few variations of your own. Let’s refer back to the first diagram that shows the whole machine. The towers can be placed inside of the circular track instead of outside. The towers may be supported by guy wires that all attach to the ground at some favorable location that is also inside of the circular track. In this case, the rotor blades run outside the circular track rather than inside. Only the upper ends of the airfoils are joined together in this variation. The lower ends extend toward the ground beneath the lowest circular track, and are not attached to anything.

Speaking of joining the ends of the airfoils, consider the possibilities that become available if all of the ends of the airfoils are uattached:

Straight Airfoil, Both Ends In Track

Now the rotor blades are not constrained to circular motion. Suppose there’s a site with predictable winds:

Oblong Track Increases Energy Capture for Prevailing Winds

Even at sites where the wind direction isn’t predictable, there may be other reasons for choosing a path that isn’t circular. In this case, given unpredictable wind direction, the path would be designed so that the blades travel an equal distance in every possible direction. You could route the blades past some kind of obstruction… heck, let ’em meander through town to showcase the mayor’s commitment to renewable energy. Shoot ’em through the elementary school and let each kid have a blade of her own. When the wind isn’t blowing she can give her blade a name and then fingerpaint it. Run ’em by the Lion’s club for a fundraiser auction where ordinary citizens can bid on a blade for the environment. The winner gets his name on a little gold plaque stuck to the blade like they do with bricks. Investors will readily agree that a Hundred Mile Per Hour Symmetrical Darrieus Airfoil has a way more pizzazz than some stupid brick. I bet they’ll be pushing and shoving, necks craning to see the auctioneer up on the stage. This thing could turn into a veritable bonanza for environmental awareness, not to mention funding the diversification of the nation’s energy portfolio.

Okay, let’s put the crowds of wildly cheering treehugger groupies aside for a moment and return to the issue of scalability. Now tell the truth – when you read the very first sentence of this blog post, did you roll your eyes when I called this machine “almost infinitely scalable”. You did? Well… did I lie? Yes, I guess I did lie… for now you know the astonishing truth –

The turbine proposed here is infinitely scalable.

The Infinitely Scalable Turbine (Dramatic Illustration)

The non-circular path is interesting, but is it practical? Absolutely! It’s easy to construct a non-circular path that is very practical. All you have to do is connect a bunch of 180 degree arcs of alternating polarity, and throw in a few 45 degree arcs to make it work:

Practical Non-Circular Path

Huh!? What’s so great about this!? Here’s a diagram that shows why this path is practical:

Analysis of the Practical Non-Circular Path

If the path of the Scalable Darrieus is circular, and if the circle has a very large diameter, then blades will be moving nearly directly into the wind and directly out of the wind for a long time before they reach the power producing part of the arc. This may present a problem if certain combinations of ideas from the Salient White Elephant blog are selected. But in this case the problem can easily be remedied with the 180 degree arc segment idea:

A Nearly Ideal Large Diameter Circular Path

If blades drive magnets in a direct drive implementation, then there is another way to improve the performance of a large diameter circular track – turn off all of the coils that are on those portions of the track that are nearly parallel to current wind direction.

Before leaving the subject of the path taken by rotor blades, I want to raise an interesting question. Obviously, the designer will select the smallest number of towers that are possible with the given type of turbine. With this in mind, imagine the blades follow a square path (requiring 4 towers). Now if the wind blows directly along two sides of the square, then the blades are producing nothing but drag for 50% of their cycle. If an oblong path is selected (requiring two towers, one at each end), then the wind might blow down the long dimension of the oblong path, which means the blades will produce nothing but drag for virtually 100% of their cycle. But if we select a triangular path, the worst case has the wind blowing directly down one side of the triangle, which has the blades producing nothing but drag only 33% of their cycle. So 4 towers = 50%, 3 towers = 33%, 2 towers = 100%. What does this strange sequence mean? I don’t know!

It would seem there are many applications for these somewhat arbitrary paths that are like a “wind turbine fence”. Imagine, for example, putting one of these fences on top of a building. As I drive around the city of Ottawa, I see a great many buildings that could support a “turbine fence” of sizable output. And it doesn’t seem the machine would be in the way of anything, or be dangerous in any way.

Here’s a guyed variation that has the blade follow a large circular or oblong path, or the ” nearly ideal large diameter circular path” just described:

X-Blade

As you read on, you may be shocked at the bizarre variations that are possible with the Scalable Darrieus concept. Your first impression may be that these ideas are interesting, but not very practical. I urge you not to dismiss this post too quickly – first impressions can be misleading. But here I’d like to say that there are so many compelling variations of the Scalable Darrieus concept, I find it difficult to adequately address details like blade synchronization without turning this post into a 500 page novel. With this in mind, I’d like you to question whether the airfoils need to be absolutely synchronized. Is there any other way? Well, I can think of two other possibilities. The first is to devise a means for preventing the airfoils from getting closer than, what… 20 feet of each other? Having prevented the airfoils from getting too close, they are left to make their way around the track on any schedule that suits them. (Balancing mass about a rotational axis is not an issue when the radius is very large.) The second synchronization concept synchronizes groups of airfoils, and then prevents the groups from getting too close to one another. In this embodiment, groups of (say) six airfoils move at the same velocity, but the velocities of the groups can differ.

Another issue I haven’t addressed is how to start the machine. I hope to have more time to fill in the details later.

Well why stop at airfoil auctions and arbitrary paths!? We’re on a roll now folks, so let’s put the pedal to the metal and blow this popstand wide open! At sites where the wind has one predictable behavior during one season, and different predictable behavior in another, simply build two tracks and then switch the blades with the changing seasons. And if it has one behavior in the morning and another in the afternoon, throw a switch and direct the blades down the alternate track. If it’s hard to believe this will work, remember that 500 ton freight trains pulling 70 cars are switched from one track to another in exactly this manner every single day!Switchable Alternate Tracks

Here’s another idea for optimizing the path based on current wind direction:

Switchable Tracks With U-Turns Allow Optimum Paths For Current Wind Direction

Or what about an offshore variation in which a floating oblong track is yawed so that its longer dimension is at a right angle to the approaching wind:

Floating Oblong Track Optimizes Energy Capture Given Wind Direction

If only a single blade is used, then the long dimension of the oblong track can be used for both blade directions. When the blade approaches the somewhat circular end of the track that turns the blade around, a switch routes it to one side of the fork. This switch toggles its polarity as the blade goes round the nearly circular end, thus routing the blade back down the long straight part of the track.

Track For Single Blade That Uses Track Switching To Reverse Blade Direction

And given we can switch between tracks, why not have a short detour track with an automatic blade washer on it? An airfoil is diverted to the blade washer once every other day or something like that.

We can add another short detour that inverts the blades. This allows us to leverage the superior aerodynamic performance of asymmetrical airfoils:

Blade Inverting Track Permits Asymmetrical Airfoil

And the blade inverting track:

Blade Inverting Detour Permits Asymmetrical Airfoils

But what if we want to invert the blades at a location that changes from one hour to the next? There’s a technique for doing this too! In fact, this technique is so cool that I decided it deserves a post of its own. That post describes how the technique would be applied to the traditional Darrieus design, but it will work just as well on the infinitely scalable turbine. Here’s a link to the airfoil inverting post.

Cable Driving Variation

In order to understand this version, you really should read the the airfoil inverting post first.

Cable Driving VAWT (Aerial View)

Airfoils Pulling Cable

Asymmetric Pitched Airfoil Detail

Cable Driving Darrieus, Airfoil Rounding Tower

Now I will describe the airfoil inverting mechanism that allows the airfoil to go round the tower. Imagine the airfoil in the last diagram above is approaching the tower. A helical guide inverts the airfoil. The helix starts at 12 o’clock. As we move closer to the tower, the helix rotates in the clockwise direction until it reaches 6 o’clock. The top blade of the airfoil in the above diagram makes contact with the helix at approximately 12 o’clock. As the blade moves closer to the tower, the helix pushes it in the clockwise direction until it has been inverted. After it has been inverted, it reaches the wheel and rounds the tower. If the wind were blowing in the opposite direction, the airfoil would already have the correct polarity for rounding the tower. In this case it will not make contact with the helix. If the wind direction is parallel to the cable, the vertex of the “V” of the airfoil will be pointing skyward. In this case it will not make contact with the helix until approximately 3 o’clock, whereupon it will be rotated 90 degrees in the clockwise direction, and then it will round the tower.

Here’s an alternative approach that does not require the airfoil to be inverted as it goes around the tower. In this approach, the rims of the wheel that drives the generator (i.e. the two parts with the largest radius) are padded with hard rubber or something like that. If the airfoil has the polarity shown in the diagram below, then the low pressure side of the airfoil just rides on those padded rims at it turns the corner.

Cable Driving Darrieus, Airfoil Rounding Tower

This approach still requires a way to insure that the airfoil is in its “power producing orientation”, though it doesn’t matter which polarity it has. If not in its power producing orientation (as in traveling directly into or out of the wind), then it must rotated 90 degrees before it reaches the wheel.

Note that the airfoils in this machine travel at what we normally think of as “tip speed”. Since this velocity is very high, the drive system depicted above is a direct drive system that does not require gearboxes.

Yet another variation looks a lot like the one just described, except the cable doesn’t move. In this variation, the airfoils slide along the cable. An interesting aspect of this approach, as well as the one just described, is that the cable doesn’t necessarily have to be all that tight. If it sags a little bit, the airfoils will hoist it up somewhat as they make their way between the towers. As for how the airfoils in the stationary cable embodiment drive the generators, perhaps one of the direct drive systems described in the next section of this post could be employed.

Before leaving the discussion of the approach wherein the airfoils are suspended on cables, I’d like to make a point about the nature of the technology described in this post. Suppose you are a scientist with a Cray Supercomputer. Though your supercomputer is mighty impressive, you’re wondering how to build an even bigger one. What would you think of the possibility that a bunch of cheap desktops in houses and buildings around the globe could be connected with a network and rival the computational firepower of your Cray machine? If gearboxes, rotors, and generators are getting to be so large and heavy that we can’t find a crane to lift them, why not consider an approach that is more distributed in some way? I have described the turbine of this post as “infinitely scalable”. I almost feel that I have “cheated” in order to realize this goal, much in the way the Cray Supercomputer guy might say “hey, you didn’t tell me I could use more than one computer in my design – that’s cheating!”. And yet if it’s possible to build a large wind machine with a lot of off-the-shelf directly driven 100 kW generators, then at least we won’t have any trouble hoisting them up onto the towers!

Direct Drive Concept

For many years, I tried to dream up a way to use the high speed tips of a horizontal axis wind machine’s rotor blades to directly participate in the process of generating electricity. Perhaps magnets would be embedded in the blade tips, and the coils would be arranged so that the blade magnets passed close by. This would truly be a “direct drive” machine. I’m not sure if the idea I am proposing here should be called “direct drive”, “semi-direct drive”, “almost and for all practical purposes direct drive”, or what. I won’t address the philosophical question of terminology here. The aim is to capture the benefits, or at least most of the benefits, of a direct drive design. I’m not sure whether I’ve achieved this; read on and you be the judge. Recently, I realized that instead of trying to find a way for the rotor blades to directly participate in the process of generating electricity, maybe I could devise a means for transferring the tremendous mechanical velocity of the blade tips to an auxiliary mechanism. This auxiliary mechanism would in turn drive the generator rotor. This is a fascinating approach, as it seems to suggest the use of off-the-shelf generators! Fantastic! In fact, it even seems to suggest the use of multiple smaller generators working in tandem. Even better!

Okay mechanical engineers… prepare yourselves… this diagram is hyper-naive:

20 MW Darrieus Direct Drive Mechanism

This drive mechanism will require a flywheel of sizable mass on the generator shaft. (Alternatively, maybe the power electronics could be designed to maintain a relatively constant generator rpm so that the blade will not collide with the spiked wheel with excessive mechanical shock.) This approach will also require an appropriately positioned wheel or roller that avoids the situation depicted above wherein the rotor blade rubs along one of the spikes in its longitudinal direction. Again, the diagram is purposefully naive, since I know a real mechanical engineer will have much better ideas for going about this than I do.

Another approach would act like a baseball pitching machine in reverse. If you’ve never seen a pitching machine, it’s actually pretty simple. Two inflatable tires, each about one foot in diameter, rotate in opposite directions. They rotate in the same plane, and that plane is parallel to the ground. The distance between the tires is maybe a half an inch shorter than the diameter of a baseball. The coach drops a baseball onto a downward sloping track, and the force of gravity causes it to roll into the space between the tires. The tires then “grab” the baseball, and it shoots out of the machine at high velocity. Here’s a drive that employs this idea in reverse:

20 MW Darrieus "Pitching Machine" Direct Drive Mechanism

Here’s an implementation for a horizontal axis machine:

Horizontal Axis Wind Turbine Semi-Direct Drive

The diagrams above have quite a few tires in order to clearly illustrate the geometry. I’m not sure this many tires would be required, and I’m not sure they’d have to be as large as automobile tires. The idea is to use as few tires as possible, and to cluster the tires as much as possible near the rotor blades’ 6 o’clock position. This is desirable because the 6 o’clock position is the worst of all positions for producing power since it is compromised by tower shadow. As the blade approaches the 6 o’clock position, it may pass some of the tires without making contact with them, but it gets closer and closer to each subsequent tire. Finally, it just barely makes contact with one of the tires, and subsequent tires push it more and more in the upwind direction. After the blade has been maximally displaced from its natural path, the tires begin to be located further and further in the downwind direction. This allows the blade to gradually return to its unimpeded trajectory. (For the sake of explanation, I have talked as though many tires are involved. In reality, the fewer tires the better.)

The tires are, of course, either coaxial with multiple generators, or else they’re all mechanically connected and drive a single generator. Will the rotor blades skid across the tires the way a car with locked wheels skids across pavement? I don’t know, but remember that one advantage of this approach is that, given power, torque and speed are inversely related. So high speed means low torque! Another point to be made here is that bouncing of the rotor blade may be minimized by providing multiple levels of tires, each with a small angular phase shift relative to its upstairs and downstairs neighbors:

Horizontal Axis Wind Turbine Semi-Direct Drive With Multiple Tiers of Automobile Tires

Yet another variation attempts to minimize the aerodynamic interference of the tires by stacking them all in a single vertical column that is centered about the rotor blades’ 6 o’clock position. In this case, each tire rotates at a different rpm, and therefore drives a separate generator. (Alternatively, all tires can drive a single generator if each tire has a different diameter.)

Horizontal Axis Semi-Direct Drive With Single Column of Automobile Tires

One drawback to the drive mechanism just described is that it must yaw with the rotor. One way around this problem is to employ a single large “tire” that encircles the tower, and that rotates about the tower. Or several tiers of tires encircle the tower, and each rotates at a different rpm and has its own generator.

Of course, given the precision with which Scalable Darrieus blade motion may be controlled by the circular track, a more conventional (à la Enercon, Bergey) direct drive design may also be possible. (I hate to call the Enercon and Bergey drives “conventional”, since they are just so absolutely cool. But since they’ve been around for a number of years, I guess maybe they’ve earned the title.) In this more conventional approach, the Darrieus blade propels permanent magnets at high velocity near stationary coils that are embedded in or supported by the track. The moving parts in this drive are aerodynamically isolated from the wind that flows through the rotor by hiding them inside the circular track.

I have much more to say about this drive, and many variations to describe, but I’m tired now so I’ll update this post in the next few days with more info.

Advantages of the Scalable Darrieus Turbine

  • Little Centrifugal Blade Load
    There are two ways of scaling this machine – increase the height and increase the diameter. As previously demonstrated, the diameter can be arbitrarily large. When the diameter is large, blade motion is nearly linear. In this case, the large centrifugal loads that a traditional Darrieus must support are virtually non-existent in the scalable machine.
  • The Scalable Darrieus Can Exceed the Betz Limit
    As long as we’re going to be infinitely scalable, investors will eagerly agree that we may as well travel faster than light while we’re at it. If a sufficiently large diameter is selected, then the streamtube is re-energized by the time it reaches the downwind side of the rotor. The rule of thumb for separating horizontal axis turbines is that two turbines should not be closer than two or three rotor diameters. Apparently, after the streamtube has traveled two or three rotor diameters beyond the turbine, it will have absorbed kinetic energy from the surrounding wind to the extent that its energy density will have roughly returned to its original value. It’s easy to see how this will apply to a very large diameter Darrieus. Simply imagine a ridiculously large turbine. Say for example that the diameter of a Scalable Darrieus is equal to the diameter of Washington, D.C. Do you really think the wind that passes through the center of this machine (near the axis of rotation) will still be traveling with decreased velocity by the time it reaches the downwind side of the rotor? (It is of the utmost importance at this juncture to clearly distinguish the wind that passes through the nation’s capital from the wind that is generated from within its borders.) From this illuminating example we can see that the maximum fraction of energy that a very large diameter Darrieus may extract is 2 x 60% = 120%. Darrieus rotors have a reputation for delivering lower efficiency than their horizontal axis cousins. However, given the doubling of the ceiling on energy extraction, it is reasonable to believe that a very large diameter Darrieus may prove to be quite efficient. This is wonderful news, since one frequently cited reason for the gradual disappearance of the Darrieus from the windfarm landscape is that it has the larger weight per power ratio. The extraordinary scalability of the Darrieus described here may very well reverse this state of affairs.
  • Efficient Use of Rotor Blades
    The first diagram in this blog post depicts rotor blades that look more or less like the blades of a traditional Darrieus rotor. But it is obvious that this shape is not required for the Scalable Darrieus configuration. It would be perfectly reasonable to design a rotor with blades that are nearly vertical, like the blades of the so called “H Rotor”:H RotorThe H Rotor is very attractive from an aerodynamic point of view, but from a mechanical point of view it’s terrible. This is so because as its blades bow out, seeking the troposkein shape, a tremendous load is applied to the horizontal beams that support the blades. This load is in exactly the direction that the beams are least able to support (tending to pull the ends of the beams together). However, this is not a problem for the Scalable Darrieus rotor. First, the lever arm for the loads supported by the H Rotor beams is very long (extending from the tower to the blade). But exactly the opposite is true with the Scalable Darrieus design – the tower is close to the blades rather than the axis of rotation. Second, if the diameter of the Scalable Darrieus is large, then centrifugal loads are small, and the centrifugal load is partly responsible for the large vertical loads supported by the beams of the H Rotor. (The aerodynamic load is also responsible for this vertical load, and both the H Rotor and the Scalable Darrieus must bear this load.) The upshot is that the Scalable Darrieus rotor enjoys the favorable aerodynamic properties of the H Rotor, while suffering little of its mechanical drawbacks.

Getting sleepy… more advantages to come….

The Cheapest Electricity in the World

I’ve heard that hydro-electricity produced in the northwestern United States is the cheapest electricity in the world. I don’t know if this is still the case, but I think it was at least true for many many years, wasn’t it? The problem with hydro is that we have only a limited supply of it – they aren’t makin’ any more rivers. But the scalability of the Darrieus machine described here brings the nature of the wind resource into sharp focus. It is virtually unlimited. The challenge is continuing to overcome limitations in our ability to harvest it. In the early days of wind energy, people used to say “the wind is free”. One time I said that to a crusty old engineer who had been a leader in the development of the modern wind machine. He just gave me a stony look and said “yeah, but you can’t afford a wind turbine”. It saddens me that he’s not around to see that his years of fighting for a noble but unlikely cause really meant something. These days the scale of wind technology and its reliability increase every year, while the costs are falling dramatically. No one can fail to be impressed with the progress that dreamers, designers, and 10 below zero storm wind hands-on and practical 200 foot tower climbers have made in this field. And yet somehow it seems like there should be a way to push the increment well beyond the current 3 or 4 megawatts a pop, and up to the scale of some of the traditional power plant technologies. If it were possible to build a gigantic “history channel sized” civil engineering project with (say) 20 or 30 super-honkin’ 20 megawatt Darrieus machines in the Texas Panhandle… no…

Nooo…

NOOOO!!! NOOOO!!! A THOUSAND TIMES NO!!! Let’s find the biggest, stinkinest, 500 Megawatt smoke belchin’ power plant in the home of the free and the brave, buy up all the property around it, and use the 180 degree arc idea to surround that rattlin’ heap o’ scrap-iron WITH A ONE BOHUNKIN’ GIGAWATT SCALABLE DARRIEUS NO TRESSPASSIN’ FENCE!!! How better to showcase the power of wind and wind engineering to rival the output of a traditional power plant? And besides, it speaks to the most fundamental precept of uncivil engineering… indeed, of survival in the concrete jungle itself…

SIZE = RESPECT

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March 14, 2009

Tulip Darrieus

Tulip Darrieus No Wind Rotor Stationary
Tulip Darrieus, Rotor Spinning and Producing Power

Tulip Darrieus (aerial view)

If necessary, the controller actuates the arms that extend from the tower and that the guy wires are attached to, moving the point of attachment further or closer to the tower as the rotor turns.

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