Salient White Elephant

May 12, 2009

Jet Stream Ram Air Wind Turbine

In earlier posts I have mentioned that a turbine capable of harvesting the energy of jet streams would probably be better for newspaper headlines than for an economical approach to wind electricity, since it would probably be cheaper and more effective to build several smaller low altitude turbines than a single monster that could tap into the jet streams. But it got me to realize that there are no jet stream turbines on the Salient White Elephant. This is Salient, to be sure, but is it White Elephant? Certainly not! And already I can hear not a little hubbub from the Canadian Parliament behind me patting their tables and gushing heah heah! So let’s just round things out with a couple of jet stream turbines before tensions run too high and one of the hairs on the head of the Right Honourable Stephen Harper springs noticeably out of place, shall we?

Jet Stream Ram Air Wind Turbine

For some reason, I’m usually biased toward using suction rather than high pressure in my flow accelerator ideas. But one advantage of using ram air pressure in the machine proposed here is that it would keep the long fabric tube inflated. This is very significant of course, since one of the biggest challenges in designing an airborne turbine is keeping weight to a minimum. Using high pressure might eliminate any rib-like supporting structure that would otherwise be required for the tube. I guess you’d have to stabilize the fabric tube by attaching it to the tethering cables at various intervals, but who knows… maybe somebody can design a way around this requirement.

Triple Tethered Variation

Jet Stream Ram Air Wind Turbine, Triple Tethered Variation

Multiple Blimps Variation

There are many variations of the ideas proposed here, but let me discuss one in particular. This idea emphasizes a technique I’d like to use to bring these pie-in-the-sky airborne turbines a little closer to feasible. Imagine eight blimps. Each is tethered by at least three cables to keep the blimps from moving around too much. An aerial view would reveal that the blimps are situated at the vertices of a gigantic octagon. It is important to note that the “diameter” of the octagon is far from insignificant. I can’t give you a number… maybe two or three football fields? Each blimp has a parachute and a high pressure tube, just as described above. All of the high pressure tubes converge at the center of the octagon, where they connect to a single larger high pressure tube that takes the jet stream wind down to the ground.

What’s so great about this variation? Well… let me first list what I believe may be the salient objectives of airborne turbine design:

  • If possible, no moving parts in the air.
  • If possible, no fiberglass, electrical cable, gearboxes, drive shafts, or electrical generators in the air. (Ever notice how the components of a wind turbine that have to do with mechanical and electrical power are about the most dense (heaviest) things known to engineering kind?!)
  • MINIMIZE WEIGHT, MINIMIZE WEIGHT, MINIMIZE WEIGHT!!!!!!!!!!!

So the idea here is that instead of having eight different tubes, we attempt to minimize weight by having a single large tube carry wind from the jet stream to the ground. This is desirable because the really long distance is from the jet stream to the ground. Once at the center of the jet stream octagon, it isn’t much further to the blimps. So could we use this trick to reduce the overall weight of the machine?

Well, whether this trick will work or not… I think you see my point. What is needed is a kind of linear programming style optimization that minimizes weight of fabric per kilowatt of capacity.

Can We Really Reach the Jet Stream?

No. The jet streams are like 30 to 40 thousand feet off the ground. (The cruising altitude of jet airplanes!) So we can’t reach the jet stream with the design proposed in this post. But we can certainly reach a higher altitude than today’s state of the art wind turbines! If you want to see a more practical configuration that uses the principles described in this post, check out the Practical Artificial Pressure Differential Wind Turbine.

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May 10, 2009

CounterRotating Direct Drive Wind Turbine

A number of posts to this blog describe turbines (both HAWTs and VAWTs) having blades that are supported at the high-speed blade tips rather than at the low speed parts of the blades. This is usually accomplished by having a blade tip engage some sort of slot that is cut into a blade guiding track, so that the action is somewhat reminiscent of the way a rail guides the wheel of a train. One of the biggest problems with this approach is how to come up with a simple, reliable way of converting the kinetic energy of the blades to electricity. The conversion apparatus should not be unweildy or cumbersome, and should not require too much hardware. (For example, in some of my earlier posts I have suggested distributing generator windings all along a very lenghty blade guiding track. This is clearly undesirable because it would make the tracks very heavy and very expensive.)

I think I may have stumbled on a good way to deal with this problem just a minute ago while writing the post entitled: Skyscraper with H-Rotors. I didn’t do a very good job of describing the counter-rotating drive idea in that post, so I’ll attempt to do a better job of it here. (Although the technique described here may be applied to many of the HAWT and VAWT turbines proposed on the Salient White Elephant, you might want to read Skyscraper with H-Rotors first, since I’ll draw the diagrams and everything assuming that we’re applying the counter-rotating direct drive idea to that particular turbine.)

Counter-Rotating Direct Drive Wind TurbineThis turbine produces power in pulses. Each time two blades that are traveling in opposite directions pass each other, their generator components (permanent magnets and coils) pass close to each other as well. So a pulse of power is produced when two blades pass each other. Obviously, it would be better for a turbine to produce power at a smooth constant rate. This is desirable for many reasons. For one thing, producing power in pulses applies a cyclic fatigueing load on the mechanical components, and this is obviously bad news. For another, the electricity is easier to process and manipulate if it is produced at a smooth regular rate. But I am hypothesizing that the design proposed here may be a good one because it allows blades to be supported at both blade tips, even as both tips travel at high velocity! This is a tremendous advantage. But the main advantage of this design is that although it allows blades to travel long distances guided only by slots that are cut into blade guides, it does not require for these long distances to have generator components (magnets and/or coils) distributed along these long portions of the blade guides. Instead, the generator components are compact, and are attached to the ends of the airfoils. You can think of all of the airfoils that rotate (say) clockwise as comprising the generator “stator”, while all of those rotating counter-clockwise comprise the generator rotor. Of course, another disadvantage of this approach is that slip rings would be required to get the power away from the blades and into the electrical system. But there’s another advantage as well – the fact that the generator’s rotor and “stator” rotate with equal and opposite rpm’s effectively doubles the relative speed with which the coils and magnets pass each other.

So before closing, let me address one of the biggest disadvantages of the idea proposed here – that power is produced in pulses. First of all, the fact that generator rotor and “stator” components are counter-rotating means that more pulses per second are produced than you might otherwise expect. (The more pulses the better. If we had enough pulses then they’d all bunch together and we’d have continuous power. As a matter of fact, three phase power is produced in pulses as well, yet these pulses combine to produce power that is perfectly constant. Might we find a way to exploit this three phase effect to make the power output from this machine constant? Don’t know, and too tired to think about it right now, so maybe I’ll revisit this later. But anyway it may not matter. I’m not concerned about the electrical pulsing – we can easily deal with that using power electronics. I’m more concerned about the pulsating mechanical loads, because these will fatique mechanical components and cause them to fail. On the other hand, the good news is that this pulsating load is confinded with a small space that is enclosed by the slots that guide the blades. This is good, because the more confined it is, the more options we have for dealing with the cyclic load. One option being, for example, just beefing up the support structure in that area. This is possible because, again, this area is aerodynamically shielded from the outside wind because it lives inside the slot.) Anyway, as I said, the because the blades are counter-rotating, they pass each other at a relatively high frequency. So maybe we can just design the machine to have many small blades (i.e. many blades, each having a short chord). Now when all these blades counter-rotate, we may end up with so many pulses that the output power looks like DC with a ripple on top. (Remember that adjacent blades don’t necessarily need to be separated by a constant angle. For example, just because there are (say) 6 blades that rotate (say) clockwise doesn’t mean that each adjacent blade must be separated by an angle of 360/6 = 60 degrees.)

Ring Generator Option

If the pulsating loads turn out to be a showstopper, then we can always fall back on the ol’ ring generator approach. In this case, we have the advantage that the rings are counter-rotating, thus doubling the velocity between magnets and coils.

April 25, 2009

Spoked Wind Dam

This is an extremely simple idea. Walls are built that radiate like the spokes of a wheel, and a VAWT is placed at the “axis of the wheel”. That’s all there is to it!!!

Spoked Wind Dam

If desired, the lower edges of the walls may be raised up off the ground so that the walls do not impede the movement of the combine. In this case, pillars hold the walls up off the ground.

Underground Wind Turbine

The two diagrams below show aerial views of the underground wind turbine. The first diagram omits the doors that cover the trenches.

Underground Wind Turbine

The doors are visible in the following diagram. The doors may be opened so that either long edge may be raised, while the opposite long edge remains at ground level. Because the diagram isn’t three dimensional, it might be a little hard to comprehend at first. But it is easier to understand if you keep in mind that the width of the doors is exactly the same as the width of the trench that it covers below:

Underground Wind Turbine Showing How Doors Open to Capture Wind

Horizontal Savonius Circular Wind Dam

Horizontal Savonius Circular Wind Dam

Sustainable Skyscraper

A very tall building reserves some floors for producing energy. I guess you’d have to produce a heck of a lot of energy to generate as much revenue as you could get by leasing the space instead. I haven’t crunched any numbers or anything, but since the wind might be very strong at these altitudes, I’m guessing maybe it would work. Remember that the turbines would produce power 24 hours a day, and seven days a week. The office space would only be used for a fraction of that time:

Sustainable Skyscraper, Side View

Sustainable Skyscraper, Aerial View

Even more energy can be concentrated at the turbine if some of the wind from the non-turbine floors could also be collected. This might not be as difficult as it sounds:

Aerial View of Floor Used For Office Space Showing Flow Concentrating Windows, Sustainable Skyscraper

High pressure develops on the upwind side of the building in the cavity formed by the flow concentrating windows. Much of the air will simply escape around the outside edges of these upwind windows, but a lot of it will escape by flowing in the vertical directions (both up and down). Once this air escapes by moving either up or down, it will find itself at the entrance of the flow concentrating panels on one of the power producing floors. It thus augments the flow through the pie slice shaped flow concentrator. The same thing happens (but with opposite polarity) on the downwind side of the building. Note that these outside windows may span several floors of office space. In this case, we don’t have several levels of windows. Instead, just one tall window spans however many office floors are between the power producing floors.

It also might not be that difficult to think of ways to make sure no accidents happen. For example, the windows that can swing open are certainly designed so that there’s no way the wind could ever be strong enough to tear them from the building. But just to make sure, a cable could attach to the middle of the top and bottom of each window. The other end of the cable would be right above or below on one of the power generating floors, and it could attach either to the floor or the ceiling as the case may be. An alarm is activated if ever the window detaches from the building. Now there are 4 mechanisms that simultaneously guarantee the safety of the public:

  1. the windows are designed to be strong enough to withstand any weather conditions,
  2. the bottom of the window is tethered to the building in case the design proves to be flawed and the window tears away anyway,
  3. the top of the window is also tethered,
  4. an alarm notifies the authorities if ever a window becomes detached from the building (leaving it hanging from the 2 tethering cables). If the alarm is ever triggered, the streets below may be quickly evacuated.

Narrow Flow Concentrating Channels Variation

Here’s a variation that looks like it might make better use of real estate. (A mathematical analysis should be developed to verify whether this is indeed the case.) It is difficult for me to draw this variation, so let me first present a crude drawing that has some structures omitted, then I’ll explain how it works:

Aerial View, Sustainable Skyscraper with Narrow Flow Concentrating Channels

The panel in the center of the building yaws so as to separate the upwind flow concentrating channels from the downwind channels. The height of this panel is equal to the height of the building. High pressure air in the upwind channels is forced up to the roof of the building. This air is now drawn down from the roof of the building through the low pressure downwind channels. The turbine rotor and generator are on the roof. One side of the turbine rotor faces the high pressure air and the other side faces the low pressure air. In this way, a single turbine rotor and generator converts the wind to electricity. Alternatively, several (2 or 3) rotors are positioned (say) 10 stories apart, so that each turbine converts 10 stories worth of wind energy to electricity.

April 24, 2009

Circular Wind Dam

The Circular Wind Dam first described in this post may not provide much improvement over the current state of the art. However, it lays the groundwork for some variations that I think may be very viable indeed. These variations are presented toward the end of this post, but in case you’re in a hurry, here’s a general idea of the type of machine that we will be working toward:

Circular Wind Dam, Rotated Energy Exchange Variation

Also, make sure you read the section entitled Advantages of the Wind Dam Over Current State of the Art Wind Turbines, as this section presents some very very powerful ideas.

Circular Wind Dam

A circular hallway is made of brick or concrete. It is extremely high, and it has an extremely large diameter. A number of walls block the hallway inside:

Aerial View of Circular Wind Dam, Twelve Walls Block the Inside of the Hallway

Here is a cross-section of the Wind Dam that shows one of the walls that block the hallway. The wall has a hole cut into it, and a wind turbine rotor captures the energy of the wind that flows through the hole:

Cross-Sectional View of Circular Wind Dam Showing Wall and Turbine Rotor

The outside of the Wind Dam has holes cut into it. These holes have sliding doors that are kind of like garage doors. The doors can block the holes, or they can open the holes to the outside air:

Circular Wind Dam

The holes near the upwind side of the dam and the holes near the downwind side of the dam are opened, while all of the other holes are kept closed. Now wind flows through the hallway from the upwind side to the downwind side. The wind turns the turbine rotors that are embedded into the walls that partially block the hallway, and the turbine rotors drive generators to make electricity. The turbine rotors and generators work just like the rotors and generators on a standard wind turbine, except that gearboxes might not be required between the turbine rotors and generators of the Wind Dam. This is true because the Wind Dam and the holes that house the turbine rotors have a concentrating effect on the wind, so that wind flows through the holes and turbine rotors at a much higher velocity than the velocity of the wind outside the dam.

Concentric Hallways Variation

A wall is added inside of the hallway that separates it into two hallways that form concentric rings:

Circular Wind Dam, Concentric Hallways Variation

The previous variation of the Wind Dam had holes in the outside wall – that is, the wall that faces the outside of the dam. In addition to these “outside holes”, the Concentric Hallways Wind Dam has holes that face the inside of the dam (the area enclosed by the dam). The holes facing the inside of the dam are controlled in exactly the same way as the holes that face the outside of the dam. That is, only the holes that are near the upwind and downwind sides of the dam are kept open, and all of the other holes are kept closed. Oddly, wind flows through the inside (smaller diameter) hallway from the downwind side to the upwind side.

Since wind flows through the hallways in opposite directions, we can replace the horizontal axis rotors with a vertical axis rotors. There are many ways to do this, but for the sake of making the diagram easy to draw, let’s use Savonius rotors with flat vanes. Notice that wind will always flow in opposite directions through the hallways regardless of which direction the outside wind is blowing:

Circular Wind Dam, Concentric Hallways VariationHere’s a diagram that shows how wind flows through the dam:

Circular Wind Dam Concentric Hallways Variation Showing Approximate Flow of Wind

Advantages of the Wind Dam Over Current State of the Art Wind Turbines

  • Most of your investment in a current State of the Art Horizontal Axis Wind Turbine (SOTAHAWT) is used to purchase sensitive, short life components that are difficult to design and that are easy to break. The majority of an investment in a Wind Dam purchases the structure itself – basically just a pile of bricks – and this investment will probably still be productive 100 years from today. (Think of the great hydro-dams in the NorthWestern United States.) And if somebody knocks a hole into the wall… big deal – just fill it in with a few more bricks. But suppose instead that an expensive component on one of your SOTAHAWTs fails. Suppose have to replace a turbine blade that is 150 feet long! You buy a new blade, wait 3 months for it to be manufactured, somehow get that 150 foot blade to the site and then weave it in between the other turbines, hire a crane, take the old blade down, put the new one up. You see what I mean – most of your investment might as well be stored in a crystal goldfish bowl that is balanced on top of a 300 foot FM radio tower. My goodness… how can you even sleep at night!? I don’t know how large the turbine rotor blades will be in the Wind Dam, but even if they are 20 feet long… so what? They don’t represent a significant fraction of your investment, and repairing and replacing them are no big deal.
  • The Wind Dam is virtually indestructible. It can assume a very low drag profile during storm winds by opening all of the doors in the inside and outside walls of the dam. Its drag profile may be further reduced by installing sliding doors into the wall that separates the two concentric hallways. These sliding doors may also be opened during storm winds to keep the drag profile to a minimum. No large sensitive components (rotor blades, etc) are required to withstand storm wind drag forces.
  • Wind turbine rotors, gearboxes (if required), and generators are all located inside the Wind Dam. Thus, these relatively sensitive components are well protected from wind, rain, snow, and other weather. And it would be easy to provide heating for these components during cold weather.
  • The Wind Dam is very quiet because noisy components are located inside the dam.
  • Electrical components are virtually immune to lightning strikes. This is true because these components are housed inside the dam, and because the dam has lightning rods on top to direct lightning strikes away from sensitive components.
  • The life of a Wind Dam will probably far exceed the 20 or 30 year lifespan of your typical SOTAHAWT. It is obvious that this would hold true for the structural part of the Wind Dam (the bricks). What is less obvious is that smaller rotors that turn at higher speeds that drive higher voltage electrical equipment, all of which live in the luxurious indoor environment of the wind dam, will also last much longer than the massive SOTAHAWT components that are stressed, fatigued, and pounded by wind, rain, snow, ice, cold temperature, humidity, and lightning year after year after year. Also, smaller components last longer than larger components because they are easier to design and because they are subjected to less vigorous mechanical abuse than are larger components.
  • Since the wind turbine rotors and electrical equipment live inside the Wind Dam, it’s hard to imagine the machine posing any danger whatsoever to the public. Can you imagine what would happen if a 150 foot rotor blade became detached from a SOTAHAWT? I wouldn’t be surprised if it could pierce through the roof of an enclosed baseball stadium. This also reflects in the cost of wind generated electricity. Because of the danger of accidents, SOTAHAWT components are quite significantly over-engineered. But normal safety margins could easily be justified in the design of the Wind Dam, and this will significantly lower costs.
  • An oft cited disadvantage of wind energy is that it has a very low energy density. The wind dam solves this problem. I don’t know what the water pressure is at the bottom of a hydro dam, but I know it’s huge. Water is heavy. But the fact that the energy density of water is high means that you need a lot of concrete to hold it back. Maybe your hydro dam is only as long as a couple of football fields, but it has 50 million dollars worth of concrete in it. But the wind dam is holding back something that is much lighter, so the walls do not have to be so massive. Maybe the circumference of the wind dam is 75 football fields, but since the walls are thin, they still have the same total amount of concrete: 50 million dollars worth. Warm up to the idea that the density of investment capital is directly proportional to the density of energy. Spreading energy out over a larger area does not raise the capital cost of the structure required to harvest that energy, it merely spreads the same capital cost out over the same larger area. Getting uptight about the low energy density in wind is like worrying about whether you should stack your money in a pile when you count it, or whether you should lay your dollar bills end to end across the bedroom floor. Actually, if you carpet your house with dollar bills, it looks like a lot more money than if you just put them in a greasy old stack with a rubber band. (But what about storms? Won’t the wind dam have to be massive and expensive in order to withstand storm winds? No. Consider the hydro dam. If more precipitation falls than you expected, you simply open the gates and let the water run through the dam. But exactly the same approach works for the wind dam. If there’s a hurricane, you simply open all the doors and let the wind pass through unimpeded. And if you have trouble making this approach work, remember that the light weight surfaces of a wind dam may be folded up, rolled up, retracted, or even laid down on the ground.)

Real Estate Sharing Variation

The wind dam can be built near areas that have residences or commercial activity, since there’s no possibility whatsoever of an accident, and since the noise is probably mostly contained inside the hallways. Holes can be cut into the walls so that roads can go through. In this case, the air is simply routed over the passageway in an aerodynamically friendly way. You could put a wind dam around a cornfield, and make a passageway big enough for a combine to get through.

Wind Vane Doors Variation

Instead of garage doors that roll up into the ceiling, maybe curved doors could be used instead to further concentrate flow in the hallways:

Circular Wind Dam Concentric Hallways with Wind Vane Doors

Very High Altitude Variation

Imagine an extremely tall (500 feet?) circular wind dam. It may have a single internal hallway, or it may have two concentric hallways. The very-high-altitude very-high-velocity wind causes the air inside the hallway(s) to also move at high velocity. This action may be accomplished in any of the ways depicted above: doors that open and close, curved vanes, or via some other appropriate aerodynamic components. However, once inside the hallway, the energy is transferred from the highest part of the hallway to a lower altitude region of the inside of the hallway. This may be achieved by blocking all altitudes within the hallway except for those that are (say) 300 feet or lower. Or it may be achieved by using nearly horizontal airfoils that direct the high-altitude energy downward toward the earth, or by some other kind aerodynamic hanky-panky. Bringing the high energy to the lower elevations allows the turbine rotors, gearboxes, and generators to be positioned at a lower altitude.

As stated in another post on this blog, Synopsis of the Best Design Tricks Developed to Date, if you can’t put the turbine up into the high altitude high energy wind, then bring the high altitude high energy wind down to the turbine. (I wrote that synopsis of best design tricks post in a hurry… don’t be disappointed because it’s actually not a very good post. Hope to have time to rewrite it later.)

Energy Exchange Variation

Circular Wind Dam, Energy Exhange Variation

For ideas on how to design a very tall H Rotor (Straight-Bladed Darrieus), see High Speed Centrifugally Stable VAWT. Of course, any VAWT may be used with the energy exchanging version of the Wind Dam, and the Savonius may be a good choice as well.

Another approach would use H Rotors with a horizontal axis. One end of a rotor’s axis would be anchored to the smaller diameter wall, and the other to the larger diameter wall. The rotor’s axis should be parallel to a line that extends radially from the center of the circle formed by the smaller diameter wall segments. (This is, or course, the same point that is the center of the circle formed by the larger diameter wall segments.) And, or course, the H Rotor’s axis would also be parallel to the ground. Anyway, you stack these horizontal axis H Rotors one on top of the other so that they form an “aerodynamic barrier” that extends from the ground to the height of the two walls (smaller and larger diameter walls). Since the axes of these rotors are all parallel, they can all be connected with a common chain drive. The chain extends to a sprocket which is on the generator shaft, and the generator shaft is on the ground.

Furthermore, if it is determined that HAWT rotors would provide better efficiency or this design, simply replace the 3 bladed H Rotors above with walls that can rotate through an angle of 180 degrees. Now cut round holes in these walls, and install HAWT rotors in the holes. Now rotate the wall by 180 degrees if the wind passes through the holes in the direction that is opposite the direction that the HAWT rotors are intended to act upon.

Two Concentric Circular Wind Dams, Energy Exhange Variation

Rotated Energy Exchange Variation

Circular Wind Dam, Rotated Energy Exchange Variation

I wonder if you could put some kind of a smooth geodesic dome structure on top of a Walmart to smooth out all the turbulence generated when wind pushes up vertically from the walls and tries to make the right angle turn to flowing across the roof. And I wonder if you could build a wind turbine that looks a little like the one above and put it on top of that dome roof.

Circular Wind Dam, Rotated Energy Exchange Variation

Circular Wind Dam, Rotated Energy Exchange Variation

Circular Wind Dam, Rotated Energy Exchange Variation

Circular Wind Dam, Rotated Energy Exchange Variation with Alternating Diffusor Concentrators

Circular Wind Dam, Rotated Energy Exchange Variation with Alternating Diffusor Concentrators

Circular Wind Dam, Rotated Energy Exchange Variation with Alternating Diffusor Concentrators 2

Circular Wind Dam, Rotated Energy Exchange Variation

Circular Wind Dam

Controlling Vortex Shedding

Circular Wind Dam, Control of Vortex Shedding

Circular Wind Dam, Control of Vortex Shedding (closeup)

High Altitude Variation

Suppose the wind turbine blades extend from an elevation of 50 feet up to an elevation of 150 feet. We would like for the walls of the wind dam to reach an altitude of 300 feet. This allows us to extract some of the energy from higher energy density wind at altitude. There are a variety of ways I can think of to do this, but I’m wondering if all that is necessary is to make the walls of the wind dam lean in one direction or the other:

Wall Leans to Access High Energy Density Wind at Altitude

At first, this solution would seem to be sensitive to wind direction. But I’m wondering if maybe that isn’t the case. Imagine, for example, wind flowing from right to left in the diagram above. Intuitively, it would seem that high energy high altitude wind would be driven downward towards the earth by the slanted portion of the wall. This is reminiscent of a flow concentrator. But if instead wind flows from the left to the right, high energy high altitude wind ramps over the slanted portion of the wall, reminiscent of a flow diffuser. In this later case, wouldn’t some of its energy still be transferred to lower altitude wind, albeit through the action of suction rather than through the action of compression?

Of course, it is also important to note that a certain amount of the high energy high altitude wind will be deflected downward (toward the earth) even if the entire wall is vertical (rather than having the upper part slanted).

In any case, if a leaning wall proves to be useful, note that it is easy to build one by anchoring fabric to the guy wires of a tower:

Making Leaning Fabric Wall with Guyed Tubular Tower

Better Diagrams of High Altitude Variation?

I’m not much of an artist, and I’m using 2D software to boot. But here’s an attempt at rendering one of the variations that captures energy from high-altitude winds without using tall turbines:

Aerial View of Pseudo-High-Altitude Circular Wind Dam

One Section of Polygon of Pseudo-High-Altitude Circular Wind Dam with Darrieus Rotors

Side View of Pseudo-High-Altitude Circular Wind Dam with Darrieus Rotors

Circular Wind Dam Pseudo-High-Altitude Variation #2

Aerial View of Pseudo-High-Altitude Circular Wind Dam Variation #2

Side View of Pseudo-High-Altitude Circular Wind Dam Variation #2 (wind blowing from right)

Side View of Pseudo-High-Altitude Circular Wind Dam Variation #2 (wind blowing from left)

Circular Wind Dam Pseudo-High-Altitude Variation #2 Stacked on top of Rotated Energy Exchange Variation

Just stack the high altitude part:

High Altitude Part

On top of the low altitude part:

Circular Wind Dam, Rotated Energy Exchange Variation

Put the towers inside the brick walls, and make the lower ends of the tarps come approximately to the tops of the brick walls.

Circular Wind Dam Pseudo-High-Altitude Variation #3

Aerial View of Pseudo-High-Altitude Circular Wind Dam Variation #3

Using HAWTs instead of VAWTs

Of course, HAWTs may be substituted for VAWTs in the above designs. Just block the regions of accelerated flow with walls, cut holes in the walls, and put HAWT rotors into the holes. The only other necessary modification is that you’d have to figure out a way to “yaw” the HAWT by 180 degrees. This is so because the wind may flow in either direction through the hole, depending on the direction of the ambient wind.

Non-Circular Variation

Non-Circular Wind Dam Rotated Energy Exchange VariationIf a non-circular path is properly designed, the wind dam will still be equally effective (or almost equally effective) regardless of wind direction. For an explanation of how to design a non-circular path, see the earlier post 20 Megawatt Direct Drive Darrieus.

HAWT with Torqueless Shaft

HAWT with Torqueless Shaft

April 23, 2009

Extremely Tall Direct Drive Wind Turbine

No Wind, Extremely Tall Direct Drive Wind Turbine

Aerial View, Extremely Tall Direct Drive Wind Turbine

Wind Blowing, Turbine Producing Power, Extremely Tall Direct Drive Wind Turbine

Airborne Wind Dam

A blimp suspends a giant flow accelerator with a small high-power turbine in the middle of it. In other words, a blimp suspends a turbine that looks kind of like the one described in this earlier post:

Wind Turbine with Flow Accelerating Shroud

This rotor will spin at high rpm, so it is easy to make it a direct drive machine. As described in prior posts, the bottom of the flow accelerator can attach to the top of a supporting tube in order that the blimp doesn’t have to carry the entire gravity load of the shroud and turbine. The tube is on wheels and a control system causes it to follow the blimp around with changing wind speed and direction.

Here’s another variation:

Airborne Wind Dam

Airborne Wind Dam with Lattice Support

Blimp With a Hole Variation

In this variation, the blimp has a cylindrical hole right through the middle of it (running down its longitudinal dimension). The small high-speed direct drive turbine rotor is inside this cylinder. A large shroud like the ones depicted above encircles the blimp in order to further accelerate flow through the cylinder and direct drive turbine rotor.

Airborne Wind Dam, Cylindrical Hole in Blimp

Skyscraper Variation

In this variation, the blimp is moored to the top of a skyscraper. When the windspeed gets too high the blimp simply detaches from the building and flies to a nearby airport where it lands until the storm passes. I hate to make the next suggestion, because somebody might actually do it. The blimp could be moored to the top of a mountain. This would produce a lot of visual pollution, so I don’t think it’s a very good idea.

Lightweight Electrical Components Variation

The blimp is big and round. It has plenty of room for a ring generator. Of course, you don’t need a ring generator to make this machine direct drive, because the accelerated flow through the cylinder is already sufficient for making the turbine rotor spin at high rpm. But if the turbine drives a very large diameter ring generator, then electricity can be generated with high voltage. If voltage is high, then current is low, and the weight of electrical components such as the electrical cables is minimized. (I’m assuming insulation weighs less than copper.)

Structural Electrical Cable Variation

This option develops electrical cable technology that is suitable both for conducting electrical power and for carrying a tensile mechanical load. This minimizes the weight of the mooring cable, since the electrical cable simultaneously provides both mechanical and electrical functions.

Aerodynamic Transmission Variation

The diagram below is a little ridiculous, but I’m a terrible artist, and I’m using 2D software to create these diagrams, so for this diagram I decided to come up with something that just shows the general idea. And the general idea is to reduce the weight of airborne components by using a light-weight hollow tube to moor the blimps. The hollow tube transmits the high air pressure that accumulates at the center of the dam (shroud) to the ground. A small high-speed turbine rotor drives a generator at the ground level end of the tube. The turbine rotor is high speed, and so it doesn’t need a gearbox. The airborne system carries no electrical or mechanical devices, and so it is light in weight.

Airborne Wind Dam With Aerodynamic Transmission

This idea suggests an interesting question – what happens to the Betz Limit when de-energized air doesn’t flow away from the turbine on the downwind side of the turbine “rotor”?

Of course, the aerodynamic transmission may also be applied to more convention turbine designs. Perhaps a shroud is positioned at the top of a conventional wind turbine tower, and the tower itself is used to route the high pressure air to a turbine rotor and generator on the ground.

Pressure Differential Aerodynamic Transmission Variation

A wall is added to the inside of the aerodynamic transmission tube. This separates the tube into two halves, just as though there were two tubes instead of one. One half of the tube opens on the high pressure side of the shroud, and the other half opens on the low pressure side. This pressure differential is carried to the ground where one side of a high-speed turbine rotor encounters the high pressure, and the other side of the rotor encounters the low pressure. Air thus flows through the rotor and turns an electric generator.

Cross-Section of Aerodynamic Transmission Tube Showing Transmission of Pressure Differential

Rotating Drive Shaft Variation

Hollow, light-weight, rotating tubes are connected end-to-end through universal joints. The tubes are attached to the mooring cable and so are suspended beneath the mooring cable. A high-speed rotor at the top transmits power to the ground through the rotating drive shaft tubes. The spins at high rpm so drive shaft torque is low.

Wind Turbine Gravity Drive

Filed under: Wind Turbine Gravity Drive — Tags: , — Salient White Elephant @ 3:38 pm

Wind Turbine Gravity Drive Decouples Rotor and Generator RPM

April 3, 2009

Closed Loop Direct Drive for Highly Scalable Horizontal Axis Wind Turbine

Closed Loop Direct Drive for Highly Scalable Horizontal Axis Wind Turbine

This drive system has sensors in the turbine blade that measure how much each blade is bent by lift and other forces. The shrouds that house direct drive generator windings are moved in the upwind or downwind direction in order to properly position them for the approaching turbine blade. What kinds of sensors might provide the proper information to the closed loop control system that adjusts the position of the generator windings? I don’t know. Strain gauges embedded into the blade spars that communicate with the controller via a radio link? A cylindrical cavity inside the blades that runs in the longitudinal direction and that has a laser at one end and a mirror at the other?

Another idea would give the turbine blade a permanent magnet that can protrude (longitudinally) from the blade tip. With this design, the shroud that houses the generator windings move to a location that is completely outside of the rotor disk (i.e. the swept area). As a blade approaches the windings, its magnet is pushed out of the blade tip. Once it passes the generator windings, the magnet is retracted so that it doesn’t create drag during the rest of the blade’s trip around the rotor disk.

Well it’s a couple of days after I wrote this, and re-reading it, it seems like a pretty stupid idea. I guess I just keep thinking about how once the turbines starting getting really big (1 megawatt or so), then the really sexy power electronics came onto the scene. Making this blog has proven to me that wind turbine innovation is likely to come from integrating other already well-known technologies, like power electronics. They didn’t invent power electronics for wind turbines, but once the machines got big enough to justify the cost of integrating these well understood devices and circuits, the addition of them provided much improved performance, and probably cut the cost of energy as well. So I’m just thinking that closed loop control technology might be one of the next things. Like for example, suppose it’s difficult to manufacture a giant ring generator and still maintain the tight tolerances required for good performance (given temperature changes, etc). Then maybe strain gauges of other sensors could be added, and a closed loop control system could adjust the radius of the rotor or stator at various angular positions… kind of like the way you turn the little nut-like things on a bicycle wheel to make it perfectly round and so that it won’t wobble side to side. So instead of trying to make the perfect ring generator, you just let the control system continually adjust the various tolerances based on sensor readings taken every minute or so. One thing’s for sure… pretty much every wind turbine configuration that can be thought of has already been thought of over all these centuries. So I wish I was in a position to look at how other technologies might be integrated in order to lower the cost of wind electricity… but I’m just not in a position like that. (Another thought that comes to mind is self-health checks… like they have in avionics systems… they have raised the detection of equipment failure or underperformance or abnormal performance to a high art form.)

Magnets In Rotating Shroud

Magnets In Rotating Shroud
This design is applied to the Highly Scalable Horizontal Axis Wind Turbine. I would put the rotating shroud on the other side of the nacelle, away from the blades, but that would require the mechanical power to go through the shaft, and I was trying to avoid that. I wonder if you could just have a rotating shroud with no magnets in it, and wedge its trailing edge between two tires and directly drive an off the shelf generator?

Rotating Shroud Drives Tires

April 1, 2009

Highly Scalable Direct Drive VAWT

There are many variations of the turbine described in this post. I’ll just go through the ones I have time to present one by one.

Two Cables Move With Symmetrical Airfoils

This variation may move along a polygonal path that approximates a circle.

Aerial View Showing Polygonal Path That Is Approximately Circular

Alternatively, the entire path (cables, towers, and all) may be yawed to keep its long dimension at a right angle to the approaching wind:

Aerial View Showing Oblong PathAirfoil Rounding TowerOne Of The Airfoils On Cable Between Towers

Single Cable Moves With Inverting Airfoils on Circular (Polygonal) Path

This variation moves along a polygonal path that is approximately like a circle. The following diagram shows how the airfoil center of mass is near the center of the cable. Because the gravity moment is small, the orientation of the airfoil will be controlled by aerodynamic forces whenever it is not traveling directly into or directly out of the wind. In these cases, the airfoil has only one stable orientation with respect to its aerodynamic forces. That stable orientation is the one in which the blade tips are downwind from the cable. Any other orientation is unstable. Whenever a change in the direction of the airfoil velocity vector causes it to become unstable, it will flip over to the stable orientation. This allows the use of pitched, asymmetrical airfoils. (Pitched, asymmetrical airfoils deliver better aerodynamic performance than the zero-pitch, symmetrical airfoils that are typically used on a Darrieus turbine.) When the airfoil is traveling directly into or directly out of the wind, its orientation will be controlled by the gravity moment. In these cases, the only stable orientation has the blade tips lower than the cable. From an aerodynamic perspective, we don’t care how the airfoil is oriented when traveling into or out of the wind, since in these cases it cannot produce power anyway.

Airfoils Pulling Cable

In the following diagram we can see that a gearbox is not required for this turbine. This is true because the airfoils and the cable are traveling at what we normally think of as “tip speed”. Suppose the wind speed is 20 miles per hour (mph). If the tip speed ratio is 6, then the airfoils travel at 120 mph, or 176 feet/second. If we want the generator to spin at 1,200 rpm, then the wheel that engages the cable must be about 2.8 feet in diameter, which sounds like a pretty reasonable number to me.

Airfoil Rounding Tower

The diagram above has been simplified – it does not show how the airfoil is prevented from hitting the tower or the generator. The following diagram adds a semi-circular guide that rotates the airfoil whenever its orientation is going to cause it to strike the tower or the generator:

Semi-Circular Guide Rotates Airfoil 90 Degrees Clockwise

The wheel that is closest you in the diagram above is the one that is situated at 3 o’clock. (The one with the cable directly behind it.) It is possible that the airfoil will strike this wheel exactly in its center. The design of the closest wheel causes it to move slightly upward and toward the tower whenever this happens, thus diverting the airfoil down the lower part of the guide.

Single Stationary Blade Guide Hangs From Cable, Yawing Oblong Path

Aerial View Showing Oblong PathCross-Section of Blade Guide Showing Integration of Blade Support and Direct Drive Components

Looking Down Cable at Blade Between Towers

Airfoil Rounding Tower

When an airfoil is supported at both ends using two blade guides like the ones pictured above, inverting the airfoil isn’t a big deal. It would seem at first to be impossible to support an inverting airfoil with only a single blade guide, since in this case the structure that connects the airfoil to the blade guide will always hit the blade guide’s supporting structure when going around the tower with one of the two airfoil orientations. But here’s how we get around this problem. In the diagram above, the orientation of the airfoil as it approaches the tower is such that the blade supporting structure (black) will not hit the blade guide support (purple). We wait until the airfoil has rounded the tower and is ready to begin its long linear path to the next tower, then we invert the airfoil. In other words, we wait unti the airfoil has passed the blade guide supports before inverting it. Now when the airfoil is approaching the tower on the other end of the oblong path, we invert the airfoil before it gets to the blade guide supports. For this reason, when the airfoil completes its trip around that tower, it already has the correct orientation for traveling its long linear path back to the other tower.

Another interesting twist to this variation would use a solid weight for toggling the airfoil center of mass instead of a liquid weight. In this case, the motion of the weight during inversion can be damped by adding two small holes that vent each end of the cylindrical cavity to the outside air. With this design, the weight moves slowly from one end of the cavity to the other because it must push air out through one ventilation hole and pull air in through the other. If it isn’t practical to vent the cavity without risking the intrusion of rainwater, then the holes at each end of the cavity may be connected with another very small diameter cylindrical cavity. Neither of the two cavities is vented to the outside air in this design. As the weight travels from one end of the large cylindrical cavity to the other, it must first transfer air from one side of the large cavity to the other by forcing it through the small diameter cavity.

Motion Damping Mechanism for Weight Inside Airfoil

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March 27, 2009

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 24, 2009

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.

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.

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.

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.

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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