Salient White Elephant

August 7, 2009

Summary of the Best Ideas on the Salient White Elephant

Since there are currently 127 posts on the Salient White Elephant, I thought it might be a good idea to devote this post to summarizing the best of these ideas.

Big Wind or Small Wind?

A worldwide network of inexpensive desktop computers ultimately proved to be far more powerful than the super computer. This lesson should not be lost on wind enthusiasts. However, the Salient White Elephant has proposed intriguing ideas both for very large wind turbines as well as for small wind turbines that may be deployed in large numbers. So why not experiment with both, and let the market sort the winners from the losers?

Idea #1) Circular Wind Dam

Circular Wind Dam

Advantage Over Flow Concentrators and Diffusers

Flow Concentrator and Diffuser

Increasing the outer diameter of a shroud in order to squeeze more wind through a turbine rotor causes the wind to develop greater tendency to veer around the entire structure – shroud, rotor, and all. For this reason, the laws of fluid mechanics tell us that you can squash only a limited amount of “extra wind” through the small opening that contains the rotor. But the wind dam is not subject to this limitation. Why not? Because the purpose of its flow manipulating structure is not to “contain the wind”, but rather to force it to do what it already wants to do – to veer around the entire flow manipulating structure! This effect can be increased indefinitely by building larger and larger dams. In this case, having nowhere else to go, the wind is obliged to flow around the entire structure, regardless of how big it is!

Another obvious advantage of the wind dam is that it is stationary and attached to the earth. A concentrator or diffuser must be suspended high in the air, and must be yawed with the machine. The shroud is large, poorly supported, and vulnerable to mechanical failure.

Here’s a link to the original Circular Wind Dam post. (I wonder if an offshore version of this idea would be possible in shallow water. In this case, the underwater part produces hydro power and the above water part produces wind power. One nice thing about combining the hydro and wind is that it would probably increase the net capacity factor. Also, it seems like it might be possible to design the underwater part to harvest both tidal and wave power.)

Idea #2) High Capacity Factor Wind Turbine

A very large wind turbine with a flow accelerating component (like the Circular Wind Dam just described) is designed to have a very low cut-in wind speed. The turbine is also designed to be very inexpensive through the removal of weight, leaving it perhaps even flimsy. Structural integrity is achieved by providing the machine with ample means for shedding the energy of higher speed winds, and for allowing storm winds to pass through the structure virtually unimpeded. (Perhaps a wall has slats or portholes that can open and close.)

Now because of the flow amplifying nature of the machine, it should be able to produce a significant amount of power at low wind speeds. This feature is remarkable in that it directly and significantly addresses the most glaring deficiency of wind as an energy source – it’s low capacity factor. I discussed increased capacity factor in two earlier posts entitled Capacity Factor and Very High Capacity Factor Wind Turbine.

Idea #3) Small Wind Business Model

This company (Small Wind Inc.) installs small wind turbines into people’s back yards, or perhaps onto the roofs of their homes or small businesses. However, Small Wind Inc. uses exactly the same business model as does the type of company that owns, maintains, and operates utility scale wind farms. That is, Small Wind Inc. erects, maintains, and repairs all of its wind turbines, and it sells the electricity generated by these small wind turbines to the power company. In exchange for the use of the home owner’s property, roof top, electrical wiring, wind resources, and so on, the homeowner receives a monthly check from Small Wind Inc.

Advantages of the Small Wind Business Model

  • Because Small Wind Inc. has tens of thousands of turbines in the field, it is in an excellent position to negotiate contracts with the power company. For example, it may have the negotiating firepower to be financially rewarded for the benefits of producing power at or near the point of consumption (instead of wasting energy by transmitting it over long distances through high voltage transmission lines).
  • Convincing a homeowner to put a big chunk of her life savings into an investment that is difficult to understand is a hard sell. Convincing a homeowner to climb an 80 foot tower with a pipe wrench clinched in her teeth to repair a broken wind machine is even more difficult. But it’s easy to sell someone on the idea of getting a monthly check when their only contribution is to avoid hitting base of the tower with a lawnmower!
  • Small wind machines are often considered more attractive than large wind farms. This allows small machines to be deployed in very large numbers. Coupled with the increased efficiency of generating power near the point of consumption, the small wind business model is good energy policy. The distributed nature of small wind also means that only small fractions of capacity will be offline at any given time for maintenance or repair.
  • Small Wind Inc. has experts in turbine siting. Only those homes and businesses that happen to have a good wind resource are selected as customers.
  • If 4 out of 10 homes in a small community have good wind resources, then the whole community can run on green power. Simply install 10 wind turbines on the 4 properties that have good wind resources.
  • Because Small Wind Inc.’s technicians are experts, cost of maintenance and repair of the wind machines is low.
  • Since Small Wind Inc.’s turbines may be deployed in large numbers, costs are lowered through purchasing parts and services in bulk, and economies of scale are realized in a variety of predictable and unpredictable ways.
  • Because power is produced at the point of consumption, transformers are not required to step voltage up to transmission line levels. This delivers significant cost savings.
  • Financing costs are low due to the expertise Small Wind Inc. has in this area, economies of scale, and the size, scrutability, and stability Small Wind Inc.

Idea #4) Walmart Rooftop Wind Turbine

Walmart Rooftop Wind Turbine

Though not shown in the diagram above, slats are positioned in the gap between the edge of the flat top of the Walmart building (dotted line) and the bottom of the dome roof. (This is the gap through which the ram air flows in under the dome roof.) The slats can open and close to allow or block this flow. With the wind direction depicted above, all of the slats on the left hand side of the diagram would be open in order to allow the ram air to enter from the left and concentrate beneath the dome, and all of the slats on the right hand side would be closed to prevent its escape. The original post describing this idea, Venturi Dome Baseball Stadium, has a diagram that shows how the slats work. Another post, Rooftop Wind Turbine, described a rooftop turbine for a typical residence.

Idea #5) Another Walmart Rooftop Wind Turbine

Aerial View Walmart Rooftop Wind Turbine

Simply put a Circular Wind Dam onto the roof of a Walmart store. In order to reduce turbulence, the store is first provided with a dome-shaped roof, and the Circular Wind Dam is mounted on top of the dome. The dome would look a little like the dome in the Walmart rooftop turbine described previously, but it would not have a hole and a turbine rotor in its center. Also, there would be no slats or gap between the edges of the flat top of the store and the underside of the dome.

Idea #6) VAWT Forest With OmniDirectional Flow Accelerators

Savonius Forest With OmniDirectional Flow Accelerators

Here’s the original post: VAWT Forest With OmniDirectional Flow Accelerators.

Idea #7) Highly Scalable Horizontal Axis Wind Turbine

In the diagrams below, the orange and dark blue lines represent guy wires. Comments are provided that explain which load each guy wire supports.

Downwind View, Highly Scalable Wind Turbine

Aerial View, Highly Scalable Wind TurbineThe Highly Scalable Horizontal Axis Wind Turbine is remarkable in that guy wires assist in supporting all of the large tower loads that are carried by the machine. This allows a great deal of weight and cost to be removed from the design. The original post explains in detail, and includes some very cool tilt-down versions.

Idea #8) Automatic Wind Turbine Blade Washer

Automatic Wind Turbine Blade Washer

If you don’t believe this embarrassingly simple device will work, then read the original post. You’ll be amazed that none of us ever thought of this idea until now.

Idea #9) Semi-Direct Drive Linear Turbine With Yawing Oblong Track

This one is too complicated to summarize, so I’ll just post a link to the original post that described it. But first, a word of advice – don’t be fooled by the apparent complexity of the diagrams. It isn’t as complicated as it first appears, and offers some tremendous performance advantages: Semi-Direct Drive Linear Turbine With Yawing Oblong Track.

More Good Ideas

Here’s a link to a page that is full of links to the best posts on the Salient White Elephant. That page has more links than are included the current post. Or if you’re really a glutton for punishment, you could just read every single one of the 127 Salient White Elephant posts!

Stationary Savonius Turbine

Stationary Savonius Turbine

Savonius in a Savonius

Since Savonius turbines are relatively impervious to turbulence, I wonder if the Stationary Savonius would make a good rooftop wind turbine? Can you imagine a giant Savonius in a Savonius on top of a Walmart store?

June 18, 2009

3 Spoked Wind Dam

3 Spoked Wind Dam

Pictures of Wind Dam

Found an old outdoor movie theater out in the countryside near Saskatoon, Saskatchewan, Canada. It looked very much like the way I imagined some of the wind dams I have described on this blog, so I stopped and took some pictures of it. I was very excited to see that the structure that supports the corrugated screen doesn’t seem to use very much metal! Keep in mind that this is in a high-wind area, and the screen has obviously been withstanding wind storms for many years. Also keep in mind that, unlike most of the designs described on this blog, the theater screen has no way to allow wind to pass through its surface unimpeded. So if the wind machine has a means for allowing high winds to pass through its flow manipulating surfaces unimpeded, it will require even less metal for its structural support!

The owner was working at the site when I drove up, and he told me the screen was 65 feet high. (I don’t remember how wide he said it was.)



outdoor theater near Saskatoon, Saskatchewan that looks like wind dam



outdoor theater near Saskatoon, Saskatchewan that looks like wind dam



outdoor theater near Saskatoon, Saskatchewan that looks like wind dam



outdoor theater near Saskatoon, Saskatchewan that looks like wind dam



outdoor theater near Saskatoon, Saskatchewan that looks like wind dam



outdoor theater near Saskatoon, Saskatchewan that looks like wind dam



outdoor theater near Saskatoon, Saskatchewan that looks like wind dam

June 17, 2009

Rooftop Wind Turbine

Posting from public library, so can’t put graphics into this post. Hope to add graphics later.

A residence has two roofs, one on top of the other. There’s a gap of what… 5 feet?… between the two roofs. The top roof has a hole cut into the vertex. A HAWT rotor that spins about a vertical axis is positioned in the hole.

The rotor is driven by two mechanisms – the ram air force that creates high pressure between the two roofs, and the suction created by wind that has to accelerate to go over the top of the roof. Imagine you are looking at the side of the house where you can see both halves of the roof sloping down at about 45 degree angles from the vertex. From this perspective, the vertex of the roof looks a little like the low pressure surface of the fattest part of an airfoil. The roof is smoothly curved to prevent turbulence and to maximize the low pressure that is created when wind flows from the right to the left, or from the left to the right. The top roof extends further from away from the outside walls of the house than does the bottom roof. This way, when the wind hits the side of the house, it will be diverted upward (on a nearly vertical path?), and the protruding lip of the upper roof will catch this “ram air” and direct it into the high pressure region between the two roofs. The lip is curved so that its edge is nearly vertical. This prevents the wind that goes over the top of the top roof from generating turbulence and vortices as it is forced to make a nearly 45 degree angle turn to conform to the top surface of the top roof.

As you probably already know, rooftop wind turbines usually don’t perform well because there’s too much turbulence over the roof for a typical wind turbine. I’m wondering if, properly designed, this idea could solve the rooftop turbulence problem. The worst turbulence is probably ulitmately generated by the wind that first “hits the side of the house”, but in contrast to a traditional turbine mounted on top of a house, the turbine described here actually makes use of this increased pressure, and controls the resulting flow so that it doesn’t result in a lot of turblence or vortices.

There are of course many details as well as possible variations not described here. Hope to fill in some more of this info later. In the meantime, note that a round house with a dome shaped roof might work best. Also, it seems like this idea might work for rooftops of retail buildings… like on the roof of a Walmart or something like that.


Okay folks, here’s a simple pic:

Residential Rooftop Wind Turbine

Maybe a hinged diffusor could be added to increase the amount of suction produced by the wind that flows over the top of the top roof:

Residential Rooftop Wind Turbine with Hinged Flow Diffusor

May 19, 2009

I Dream of Genie Wind Dam

I Dream of Genie Wind Dam Construction - 1

I Dream of Genie Wind Dam Construction - 2


I Dream of Genie Wind Dam Construction - 3


I Dream of Genie Wind Dam Construction - 4

Now take a bunch of the structures depicted in the last step and connect them together with arcs to form a giant circular wind dam:

I Dream of Genie Wind Dam


Drive System

Notice that since a given “Totem Pole” of HAWT rotors are stacked one on top of another, they can share a common drive chain. This common drive chain ultimately drives a sprocket that drives the generator shaft. The generator is located in a small compartment on the ground, beneath its “Totem pole” of turbine rotors.

Does This Turbine Require a Yawing System?

I can think of two variations of the I Dream of Genie Wind Dam as regards the yaw drive. The first version would always have all of the rotors turning, regardless of which direction the wind is blowing in. This would be easier to explain if I could draw a nicer 3D model, but I’m not much of an artist, so bear with me here. All rotors can rotate simultaneously because some of the high speed wind moving around the outside of the dam seeks the “smallest radial path”, meaning it will eventually force its way through a rotor to the inside of the wind dam. The wind outside the dam that does not manage to find its way into this smaller radial space will instead shoot off the bowed out end of one of the wall sections (much like the wind shoots off the trailing edge of an airfoil). This will create a low pressure region in the smaller radial locations that “suddenly appear” next to this high speed air at the moment it shoots off that bowed out edge of the wall. This low pressure sucks low speed high pressure air from the inside of the dam through the rotor that is near the high speed air that is shooting off the bowed out end of the wall.

In the variation just described, the rotors do indeed need to assume one of two yaw angles, each separated by 180 degrees. (Alternatively, the blades may have variable pitch so that they can accommodate the flow of wind in either direction through the rotor.)

The other variation would have doors that can block the “hole” that is occupied by the rotor. In this variation, all the rotors that pass wind from the outside of the dam to the inside of the dam (given wind direction) have their doors opened, while the doors of all the other rotors are closed, rendering those rotors inoperable. Or you could do it the other way around, allowing air to be sucked out of the inside of the wind dam, but not to be forced from the outside of the wind dam to the inside. In this case a yaw system is not required. This is so because the door will always be closed when wind has a tendency to flow through the accompanying rotor in the “wrong direction”.

Third World Variation

Think of how easy it would be to build a low cost variation of this machine for the developing world! Imagine that instead of building a circular dam, we’ll build one that is polygonal, with an approximately circular shape. Maybe the circle has 10 or 12 sides. So we put concrete columns or telephone poles up in the shape of the polygon. We have one set of telephone poles for the “smaller radius” polygon, and another set for the “larger radius” polygon. Now we string cable between the poles. The following diagram shows just one side of the polygon, and uses blue to represent the cables connecting the “larger radius” polygon, and green to represent the cables connecting the “smaller radius” polygon:

I Dream of Genie Wind Dam, Third World Variation, 1

Now take some of that beautiful multi-colored fabric like they have in India and wrap it back and forth around the cables to imitate the I Dream of Genie Channels:

I Dream of Genie Wind Dam, Third World Variation, 2

When wind flows around sharp edges, it tends to create turbulence. To avoid this tendency, we might like to use something with a larger diameter than cables. How about we use cheap PVC pipe? Then we can string the cables through the inside of the PVC pipe. This way the cables can provide a great deal of strength and stiffness to the structure, yet the cables will have no adverse affect on the aerodynamics.

For More Information on Wind Dams

For further information related to this idea, see the earlier Salient White Elephant post: Circular Wind Dam.

May 12, 2009

Practical Artificial Pressure Differential Wind Turbine

Explanation of Artificial Pressure Differential Turbine 1

Explanation of Artificial Pressure Differential Turbine 2

In this way we have brought the low pressure on the downwind side of the parachute to the top of the tower.

Now, in your mind’s eye, eliminate the low pressure tube, and make the parachute whole again. Now attach a high pressure tube to the vertex of the parachute:

Explanation of Artificial Pressure Differential Turbine 3

Now we have techniques for bringing the high pressure of the upwind side of the parachute back to the tower, and for bringing the low pressure of the downwind side of the parachute back to the tower. Next, we build both the high pressure and low pressure extending tubes into the parachute at the same time. The low pressure tube has the smaller diameter, and it connects to the hole in the vertex of the parachute which has the same diameter. The diameter of the high pressure tube is larger than the diameter of the low pressure tube, and it encircles the low pressure tube so that a cross-section of the two tubes makes them look like concentric circles.

The next step is to transmit the high and low pressures to the bottom of the tower using the same technique. The tower is actually two towers – an inner smaller diameter low pressure tube with an outer larger diameter high pressure tube surrounding it so that a cross-section of the two makes them look like concentric circles. The high pressure and low pressure regions are connected at the bottom of the tower and, as expected, a HAWT rotor (with a vertical axis) is positioned between the two. The rotor, gearbox, and generator are at all at ground level.

The only thing I haven’t explained is how the low pressure and high pressure tubes make a right angle turn at the top of the tower. I was planning to draw some pictures of this, but I don’t think it’s really necessary. There are probably a million ways to do this. I will just note here that the parachute part automatically seeks the downwind position, and so it doesn’t require a yaw system. The right angle joint can be yawed, or it can simply be a cylindrical piece with vents positioned radially about its center. The vents have doors in them that can open and close to simulate yawing, though few moving parts would actually be required. (To illustrate, imagine an aerial view of this machine. Suppose the high and low pressure tubes approach the tower near the 9 o’clock position. Then the vents in the cylindrical piece at the top of the tower that are at positions 8 o’clock, 8:30, 9:00, 9:30, and 10 o’clock would all be open, while all of the other vents would be closed tight and aerodynamically sealed.)

The tower supports little weight, and it can be fitted with vents to let storm winds pass through unimpeded. This means the tower can be very light in weight, very inexpensive (relative to a typical HAWT tower), and it can have a large diameter if necessary. The parachute and the fabric part of the low pressure and high pressure tubes may have similar vents so that they also create little drag during storm winds. Maybe the parachute and fabric vents could even be somehow rolled up and stored inside the tower during storm winds.

Finally, note that the tower could be incredibly high. This is true because it supports little weight, has little overturning moment in storm winds, and can accomodate multi-level guy wires that can attach to the tower at any elevation, including at the very top of the tower!

Artificial Pressure Differential Turbine

Yawing Variation

Now we might imagine a long horizontal tube extending from the top of the tower. The supporting cords that tether the parachute are attached to the end of the horizontal tube that is far from the top of the tower. This way, the “vertex” (downwindmost end) of the parachute is right at the top of the tower, and the low and high pressure regions may easily be connected to the vertical (tower) low and high pressure concentric tubes. The horizontal tube yaws to align with the wind.

There are many other variations like this. Maybe we just build something that looks like a giant radio telescope dish, and attach its vertex to the top of the tower. This might not be so ridiculous if the parabolic dish has slats that automatically open when the pressure differential between the upwind and downwind sides of the slats exceeds a safe value.

May 10, 2009

SkyScraper with H-Rotors

This is a very simple idea. Imagine a skyscraper that looks round in an aerial view. Now just put a bunch of disks around the outside walls of the building… (say) one disk every 6 stories or something like that. Now near the outer perimeters of these disks, you cut a slot as described in many of the other posts on this blog. (See for example 20 Megawatt VAWT.) The ends of the airfoils engage these slots. The blades go around the building with each level rotating with the same polarity as its upstairs and downstairs neighbors, or else with adjacent levels rotating with opposite polarity to double the speed difference between the generator rotor and the generator stator:

SkyScraper with H-Rotors

Mechanical energy may be converted into electrical energy in any of several ways. Once again, all of these conversion methods have been described multiple times on this blog, so I won’t repeat them here. I’ll just give a short list of the possibilities:

  • Generator windings are embedded into the slots. A permanent magent is attached to the ends of the blades and the motion of the blades forces these magnets past the windings.
  • Cables are attached to the middle of each rotor blade. These cables are attached to a smaller diameter cable. The diameter of the smaller diameter cable is just large enough to around the building without hitting it. The smaller cable drives the generator. All cables should be designed to carry only the power producing components of the airfoil loads. The larger (non-power producing) loads are carried by the disks that support the blades tips.
  • The slots that engage the blade tips are provided with a great many small wheels inside. Airfoil motion imparts spin to these wheels. All wheels are mechanically linked so that they all rotate at the same rpm. The rotational motion of the wheels (or of their mechanical linkage) drives a generator.

One question is whether blades that are rotating and producing power would be a visual distraction to the people inside the building. I honestly don’t know what the answer to this question would be. Because the building is high, and because the building itself acts as a flow accelerator, you can imagine that the blades might be traveling at a very high velocity indeed. I have no idea what the velocity would be, but let’s say they’re going 200+ miles per hour. Could you even see a blade moving at that speed? Anyway, if this turns out to be a problem, maybe one should explore the opposite approach – a great many blades having a slow, gentle movement.

Direct Drive Counter-Rotating Cat’s Eye Variation

In this variation, each level (each set of adjacent supporting disk-like structures) is provided with two sets of blades. Half rotate clockwise, and the other half rotate counterclockwise. (These blades may or may not be designed to imitate the behavior of the Cat’s Eye Darrieus Rotor.) The ends of all of the blades rotating with one polarity are attached to permanent magnets, while the ends of all the blades rotating with the other polarity are attached to windings. As two blades that rotate with opposite polarity pass by each other, their magnets and coils pass close to each other in a manner similar to what would be witnessed if you could look inside of an electric generator. The magnets and coils are attached to the parts of the ends of the airfoils that are hidden inside the slot, and thus create minimum drag and turbulence. The mechanical tolerances that must be maintained to minimize the air gap that the flux must traverse are acheivable also because these components live within the rigid and tightly controlled confines of the blade guiding slot.

Geodesic Dome Turbine

Start with a Geodesic Dome:

Geodesic DomeNow Cut a hole in the top, and cover the hole with a shroud that can yaw in order to keep its opening pointing upwind. Also add vents near the lower part of the dome can than be either opened or closed:

Geodesic Dome TurbineThe variation depiced above has air flowing into the hole at the top of the dome and out of the vents below. I’m not sure this is the best arrangement. The alternative would be to have air flowing into the lower vents and out of the hole in the top. In this variation, the shroud over the top hole in the diagram would be yawed (rotated) 180 degrees, and (I’m guessing) the left two vents in the diagram would be open, while the other vents would be closed. I guess one of these ideas is probably aerodynamically superior to the other, but I don’t know which is which. It’s worth noting that the real low pressure should be at the top of the dome, since this is where the wind has been accelerated the most. Seems like it might make sense then to let the wind flow in to the lower vents (where pressure is naturally higher), and out through the hole in the top. I don’t know much about the theory of fluid flow, so I’ll leave the rest to those of you who have the academic background to model and solve a problem like this.

Before ending this post, however, I’d like to point out an aspect of this idea that is particularly intriquing. Since you can have lots and lots of vents, but only one hole in the top of the dome, it stands to reason that it should be easy to provide the dome with many square feet worth of vents, given the area of the hole at the top of the dome. This means that the velocity of wind flowing through the vents may be caused to vary by only a small amount relative to the velocity of the wind outside the dome. For this reason, it would seem that the vast part of the lower part of the dome could be made to be quite comfortable for people, and this means the dome can have alternative uses. For example, the dome could house a giant botanical garden for the public to enjoy. If you really wanted to control the environment for the people inside, two concentric geodesic domes could be placed one on top of another, creating a thin (say) 40 foot wide gap between the two ceilings. The gap could be used for wind flow and the harvesting of its energy, while the part inside the lower (smallest) dome could be used for just about anything – commercial office space, a manufacturing plant, basketball court, … you name it!

Retrofit Option

Depending on how attractive this structure could be made to be, and on its cost effectiveness, we might imagine putting one of these things on top of an existing structure. Rooftop wind turbines are generally frowned upon, but I think this is mostly because of the harshly turbulent conditions within which a rooftop turbine must normally operate. The dome solves this problem in several ways. First, it doesn’t have any sharp turbulence producing edges. Second, its rotors are small and therefore less sensitive to turbulence, and they can be located in a short cylindrical shroud that is equipped with the same kinds of turbulence attenuating apparatus as is found in wind tunnels. And finally, if a small rotor does eventually develop a crack due to turbulence-induced fatique, simply replace it. It’s small, and so the cost of replacing it is no big deal.

I saw a medium sized, three story motel the other day that looked like it could easily accomodate a Geodesic Dome Turbine. If the dome had enough vents to open during a wind storm, it would seem likely that the motel could accomodate the turbine in spite of the fact that the building designers had not accounted for the extra load.

April 27, 2009

Synopsis of the Best Design Tricks Developed to Date

This is the 100th post on the Salient White Elephant! To celebrate the Salient Centenary, I thought I’d try to summarize the lessons learned and tricks developed up to this point.

  1. Reduce size, weight, and number of wind turbines by replacing turbines with AeroArchitecture (fixed structures that direct, accelerate, and concentrate flow).
  2. Instead of placing the turbine rotor at high altitude, bring the high-energy high-altitude wind down to the rotor. If it isn’t possible to bring the high-altitude wind down to the rotor, consider using the high-altitude wind to accelerate the low-altitude wind in the manner of a flow diffuser. (That is, use high-altitude wind to draw a vacuum behind the rotor.)
  3. Develop stationary flow accelerating structures that perform equally well (or almost equally well) regardless of wind direction.
  4. Increase capacity factor by maximizing size and minimizing weight of AeroArchitecture, by minimizing cut-in wind speed, and by minimizing rated wind speed. Regulate power output and protect stationary light-weight AeroArchitectural structures from storm wind damage by providing stationary structures with means for regulating the amount of wind that passes through the structure unimpeded.
  5. Further increase capacity factor by spreading turbines and structures over the widest possible geographical area. (I’m assuming here that it is more likely that the wind isn’t blowing in a single, small spot than in many geographically dispersed places.)
  6. Place turbines and other weather sensitive components inside of AeroArchitectural structures if possible. (Note that this protects turbines from lightning damage as well as from exposure to other weather.) If it isn’t possible to place turbines inside of AeroArchitecture, then try to make the AeroArchitecture taller than turbines, and then put lightning rods on top of Architecture.
  7. If the design enjoys the luxury of operating within a limited and confined space, consider using the same tricks that wind tunnel designers use to reduce turbulence.
  8. Build turbines to last for 30 years; build AeroArchitecture to last for 1,000 years.
  9. Employ airborne structures that either don’t need to move at all, or else that only need to move for the purpose of yawing. (Avoid airborne structures that move like a turbine rotor in order to harvest energy.)

VAWT Forest With OmniDirectional Flow Accelerators

This post describes a field of stationary flow accelerators that I hope will be effective for any wind direction. Flow accelerators, or shrouds, are generally regarded as closer to science fiction than to a practical and economical idea. I think this may be due to the following problems:

  • It is difficult to yaw a large structure.
  • If the yaw system fails during high winds, the structure will fail.
  • The complexity and cost of the structure are probably greater than the complexity and cost of simply scaling up a more conventional and well understood design.

The VAWT Forest with OmniDirectional Flow Accelerators attempts to solve these problems as follows:

  • The flow accelerators are fixed. They do not yaw, and they rest on the ground.
  • The flow accelerators are equipped with vents that allow high winds to pass through the structures without generating much drag.
  • The cost and complexity is low. The flow accelerators are basically nothing more than oblong shaped brick walls.

The diagram shows Savonius rotors, but the design might work with other types of VAWT rotors. However, because of the relatively unpredictable and complex flow patterns that are likely to be created with this design, I am assuming that the Savonius might be a good choice, because it is mechanically and aerodynamically robust, and because it is relatively insensitive to turbulence:Savonius Forest With OmniDirectional Flow Accelerators

What’s so great about this idea? It seems incredible that you could develop a fixed flow accelerator that is equally (or almost equally) effective for every wind direction. The trick here, of course, is that only the accelerators that are in the interior of the forest are equally effective for every wind direction. The ones on the periphery of the forest may not accelerate flow at all for certain wind directions! But the design is effective because we can make the forest very very large – with many accelerators and many turbines. In this case, the number of turbines and accelerators that are at the periphery of the forest account for only a very small fraction of the total number turbines and accelerators.

Here’s a simpler way to make the flow accelerators that might be less expensive and that still avoids making the wind flow around sharp corners:

Alternate Design for Flow Accelerators

I think this idea looks pretty good as is, but we can experiment further by putting circular shaped energy exchangers over the large empty places formed by the flow accelerators. These energy exchangers are able to rotate in order to align with wind direction. The slotted channels cause the oncoming (high energy) wind to flow down into the empty areas between the flow accelerators, and they also cause low energy air that has already flowed through the rotors to flow up and out of these empty areas in the downstream direction:

Counter-Sloping Energy Exchange Channels

Savonius Forest With OmniDirectional Flow Accelerators and Rotating Energy Exchangers

Another variation has a tarp lying across the roofs of all the flow accelerators, and places towers along the four edges of the Savonius Forest that support angled tarps. The following diagram omits the towers and the tarps that would be in the front and the rear of the view shown. (That is, only the towers and tarps on the right and left are shown – the ones in the front and back are omitted.)

Savonius Forest With OmniDirectional Flow Accelerators and Guyed Tower Supported Flow Accelerators

I am not an aerodynamicist, but I have always had the feeling that ducted rotors waste a lot of the accelerated flow created by the shroud. Wind tends to veer around obstructions. This is the reason for the Betz limit – the more energy you extract from the wind, the more you are slowing it down, the greater is the obstruction to flow, and the more the oncoming wind veers to avoid the obstruction. The idea proposed here is that more rotors should be placed in the path of the wind that is attempting to make its way around the turbines. Now I realize that this smacks of an “eternal motion” kind of logic. Isn’t it true that all of the turbines and all of the flow accelerators may be regarded as a single energy harvesting device, and that the Betz limit will apply to this large composite “turbine” just as well as to a single ducted rotor? Well… I’m not sure. The situation is complicated somewhat because the rotors are dispersed in the upwind and downwind directions as well as in the cross-wind directions. But let’s just suppose that the dispersed nature of this design is indeed subject to the same limitations as a single ducted turbine. Doesn’t it still enjoy the advantage of being omnidirectional? And isn’t it easier to design and build a number of small rotors instead of a single giant one? And isn’t it nice that the small rotors will spin at high rpm, thus reducing torque? And there is an aspect of the omnidirectional nature of this machine that I can’t quite wrap my mind around. It is as though the energy is filtered through the turbines like the way you might imagine rainwater making its way down to the aquafer. That is, if the pressure becomes unbalanced for some reason, the wind just might decide to flow in the crosswind direction. This seems possible since once inside the maze of flow accelerators, air has no “direct contact” with the wind outside the maze. (If this doesn’t sound very scientific, then you are obviously not a graduate, as I am, of the Billy Mays two week engineering correspondence course with complimentary “Senior Engineering Manager Your Name Here” wall plaque.)

There is another feature of this design that appeals to me as well. It seems to me that in the past, designers of ducted machines have assumed that a flow accelerator must be symmetrical. This seems like a critical mistake to me. One of the problems with flow accelerators is that they are huge, unweildy, expensive, and vulnerable to damage in storm winds. But the dispersed “Forest” idea shows that you aren’t constrained to expanding in symmetrical directions – you can simply ignore the vertical direction and spend your money expanding in the horizontal direction alone. Or, more likely, you can develop mathematical design techniques that can predict the optimal aspect ratio.

April 26, 2009

Flow Magnified VAWT Forest

Flow Magnified VAWT Forest

Segmented Circular Wind Dam With Adjustable Flow Accelerators

Segmented Circular Wind Dam With Adjustable Flow Accelerators

Almost all of the AeroArchitecture (non-turbine) part of this machine is fixed. The only part of the flow manipulating structure that is not fixed is the curved blue panels. The rotational angle of these panels is regulated by the turbine controller, and is a function of wind direction. I have drawn these panels at what I believe to be approximately the correct rotational angles given wind direction, but of course this is only an intuitive guess. I think some detailed aerodynamic modeling will be required to determine the optimum angles for the panels. However, let me explain the reasoning behind my guess.

Let’s begin by pretending that the adjustable panels and the turbines are not present, and that the circular wall does not have segments cut out of it. In other words, the wind is flowing around a very tall round wall. In this case the high pressure region will be around the most upwind part of the wall. The flow accelerates to get around the wall, and I think the lowest pressure will be approximately at the 3 o’clock and 9 o’clock positions. The flow about the rest of the wall is oscillatory and unstable. Vortices are shed in alternating fashion, first from one side of the wall and then from the other. For example, the flow may detach at about 4:30, and a clockwise vortex (with a vertical axis) will spin off of the wall at that point. Then the flow will detach at about 7:30, and a counter-clockwise vortex will spin off the wall at that point. Then the pattern will repeat. So the first thing to notice is that it may be desirable to add adjustable panels at 2:30, 4:30, 7:30, and 10:30 in order to prevent the vortex shedding. I have not drawn these panels because I don’t know if they will actually be necessary. Remember that the wind is being de-energized by the 4 turbines, and maybe this will be sufficient for stabilizing the flow. In any case, let’s forget about the vortex shedding for a moment, and consider the system as depicted above (with the segments removed from the wall, the curved adjustable blue panels, and the turbines present just as depicted in the diagram).

As I said, the high pressure occurs at the 12 o’clock position. As the diagram shows, the wind is flowing more or less straight at the 12 o’clock turbine. In this case, both the adjustable curved panels and the curved parts of the wall that extend downstream from the turbine act to concentrate and accelerate the flow through the 12 o’clock turbine.

Now let’s consider the 3 and 9 o’clock turbines. I am reasoning that the wind is moving slow and is at a relatively high pressure in the regions just inside the wall near these two turbines. This is true because the wind has been forced to flow through a very large cross-section inside the wall, and also because the wind has been de-energized somewhat as it passed through the 12 o’clock turbine. On the other hand, the velocity is at a maximum and the pressure at a minimum in the areas that are outside of the wall and outside of the 3 o’clock and 9 o’clock turbines. This is true because the wind has had to speed up to get around the wall, and also because it has yet to pass through any turbines, and so it hasn’t had energy extracted from it yet. Based on all this reasoning, I have elected to orient the adjustable panels so as to further encourage the flow that already wants to happen anyway – that is, the flow from slow high pressure inside the dam to fast low pressure outside the dam. When you consider what normally happens when wind flows through a turbine, you see that it is not exactly as I have described:

  • Flow through a traditional turbine is from high velocity and high pressure to low velocity and low pressure.
  • The flow that I just described is from low velocity and high pressure to high velocity and low pressure.

So maybe my reasoning is flawed. Of course, the rules will be changed when flow is manipulated, and in this case we are not only manipulating the flow, but we are manipulating it a great deal with a very very large structure. So I guess the only way to figure out whether my reasoning is correct is to build a sophisticated aerodynamic model and see what it says. Anyway… if you take a look at the hypothetical path of flow I’ve drawn near the left side of the diagram, you can see that the flow will be exiting the trailing edge of the adjustable panel at high velocity, just like the way air exits the trailing edge of an airplane wing. So I am reasoning that this flow will draw the dead air out of the inside of the dam and through the turbine.

Now for the 6 o’clock turbine. This one seems pretty straightforward. On the one hand, you might expect that the adjustable panels and the fixed curved parts of the wall that extend upwind of the 6 o’clock turbine should together look exactly like the flow accelerating structure around the 12 o’clock turbine. The reason I haven’t drawn it that way is because assuming we are able to successfully prevent the flow from detaching from the wall and spinning into a vortex, then the flow will be wanting to curve in the downstream direction as it continues its journey away from the wind dam in the downwind direction. In this case, the panels need to be rotated toward this path somewhat so that the flow doesn’t collide with the most downwind end of the adjustable panel and spin off of that sharp edge in a vortex.

April 25, 2009

Very High Capacity Factor Wind Turbine

Filed under: AeroArchitecture, Wind Turbine Capacity Factor — Tags: , — Salient White Elephant @ 10:18 pm

This post describes a means for greatly increasing the capacity factor of an AeroArchitecture Wind Turbine, such as the Circular Wind Dam. The concept is very simple. The fixed structure of the wind turbine is extremely large, yet very flimsy. For example, the walls of the Circular Wind Dam are made to withstand winds that blow no faster than 20 miles per hour! Because the walls are so flimsy, they are very inexpensive. What happens when the wind blows faster than 20 miles per hour? Vents in the wall are opened to let some of the wind pass through. The turbine hits rated power when the wind speed reaches 20 miles per hour. When the wind speed exceeds 20 miles per hour, power is regulated using exactly the same mechanism – vents are opened just enough to prevent the generators from overpowering.

If you have a million dollars to spend on the fixed structure of an AeroArchitecture Wind Turbine, you spread that money over the largest possible geographical area. Every square foot added to the size of the fixed structure provides an increase in the capacity factor of the machine.

One very interesting twist to this design technique is whether to spread the cost of the fixed part of the turbine over a single very large wind turbine, or over multiple flimsy structures that are located relatively far apart. I suppose the wind is even more likely to reach cut in speed if only the average wind speed at all the different wind turbine locations needs to be considered. Of course, this also spreads the transmission lines over a larger area. So you can see that some sophisticated computer modeling would be required to develop the optimum design.

Another intriquing question is whether to use the capital cost of the fixed structure to expand in the horizontal or vertical direction. It would seem that you could increase the size of the structure more if the increased dimension is in the horizontal direction (the structure is wider) rather than in the vertical direction (the structure is taller). But of course the extra wind harvested has more energy if you expand in the vertical direction. So again, the best design choice is not obvious, and a sophisticated means for developing this aspect of the design is desirable.

And finally, I wish I could see come kind of mathematical analysis that validates or refutes the fundamental principle behind this post – that the use of flow concentrators can increase capacity factor. My reasoning is only intuitive; it is not scientific or quantitative. It is known that a flow accelerating (upwind) shroud or a flow deccelerating (downwind) shroud increases the speed of wind that passes through the rotor disk. This must be so, of course, to maintain a constant volume rate of flow. Say for example that the cut-in speed for the rotor is 10 miles per hour (mph). If a shroud multiplies velocity such that a 5 mph wind becomes a 10 mph wind at the rotor, then isn’t it true that the cut-in speed has been reduced from 10 mph to 5 mph? And if so, doesn’t this mean that a flow manipulating shroud is capable of increasing capacity factor? This may seem like a minor point when you consider that there isn’t much power in a 5 mph wind or a 10 mph wind, but doesn’t the same mechanism apply for any windspeed? For example, doesn’t this reasoning mean that all of the time that the wind blows 10 mph means that the rotor spends the same amount of time harvesting a 15 mph wind? (I realize that the flow accelerating effect probably isn’t linear, but that’s just a detail.)¬† In fact, it seems to me that one of the challenging aspects of designing this type of machine is how you would bleed energy away from the rotor at higher wind speeds, while still allowing the rotor to safely and reliably harvest an amount of energy equal to its rated output. (This would be necessary because, if it is our desire to increase capacity factor, then we wouldn’t want to lose the productive hours at higher wind speed simply because those winds don’t occur very often. Aiming for high capacity factor, we want the machine to be producing power in the highest number of different possible conditions. As a matter of fact, seems to me that it may also be possible to add a little bit to the capacity factor on the high end of the wind speed spectrum. This is true because the rotor is small and therefore, from a mechanical perspective, it is very robust and very strong, and also because wind velocity may be regulated somewhat by opening vents in the shroud.)

One final point. If the flow manipulating shroud is very large and very expensive, then it may be desireable to add a few rotors and generators so that some of the energy that would have been allowed to pass through the shroud during high winds could be harvested by the extra rotors or generators. This would do much for the capacity factor of the machine, but since the energy is there, and since you only need a small rotor and supporting equipment to harvest it, then it may be cost effective to do so. I’m glad I included this paragraph because, if nothing else, it illustrates how much of the complexity of the design of a very high capacity wind turbine has been shifted from areas like blade resonance and tower resonance, to a much more hazy problem of optimization, such as might be solved with linear programming.

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

Venturi Dome Baseball Stadium

Filed under: AeroArchitecture — Tags: — Salient White Elephant @ 11:54 am

Venturi Dome Baseball Stadium

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.

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