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!

June 18, 2009

3 Spoked Wind Dam

3 Spoked Wind Dam

April 29, 2009

Flow Accelerator that Yaws by Force of Drag

VAWT with Shroud that Yaws by Force of Drag

HAWT with Shroud that Yaws by Force of Drag

April 27, 2009

Wind Turbine With Blimp Supported Flow Accelerator

Wind Turbine With Blimp Wind Turbine With Supported Flow Accelerator

Wind Turbine With Blimp Wind Turbine With Supported Flow Accelerator

Ultra High Altitude Low Visual Pollution Variation

There are a few problems with the turbine just described:

  • The weight of the suspended tarp may be prohibitive.
  • The tarp resource is poorly leveraged because much of the wind it redirects is low-energy wind that is close to the ground.
  • The blimp resource is poorly leveraged because much of its size and weight stems from the need to support the large part of the tarp that is close to the ground.
  • The blimps are not able to fly at high altitude because the tarp would simply be too heavy to lift to high altitude.
  • The exceedingly powerful suction developed by such a large flow accelerator may reverse the flow that is near to the ground and not too far above the turbine and the lower edge of the tarp.

This variation proposes to solve these problems and permit extremely high altitude wind to be harvested:

Wind Turbine With Blimp Supported Flow Accelerator, Side View, High Altitude Variation

Wind Turbine With Blimp Supported Flow Accelerator, Side View, High Altitude Variation

Now the blimps and tarp may be separated from the turbine by a very large vertical distance, and the suction is carried to the ground through light-weight fabric tubes that are supported on the guy wires. As an alternative to the design shown above, one tube can be fixed to carry high pressure and the other can carry low pressure. The turbine is then placed between the openings of these two tubes at ground level.

I wonder if this design or something like it would be capable of reaching the jet streams? I guess that’s pretty outrageous, and probably not even necessary. (It may be more economical to harvest lower altitude winds using several machines than to build a single gigantic machine that reaches the jet stream. Plus you’d have the safety issue – what if a cable breaks? Of course, I guess you could always put it out in the ocean. Another potential problem with extremely high altitudes is that the wind direction up there might not be the same as on the ground. But then again, if you’re getting so much energy from altitude, you could just put the turbine rotor inside the tube, and also put the rotor on the ground so that it doesn’t have to yaw. This way the wind velocity near the ground would be insignificant compared to the velocity of air moving through the tube, and so it wouldn’t matter which way the rotor were pointed, or which way the opening of the tube were pointed. In fact, you could use a HAWT rotor that spins about a vertical axis, and let the tube extend from the rotor in the vertical direction.)

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

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

Shielded VAWT

This post proposes to increase the efficiency of a VAWT with yawing shields. In the case of the Darrieus, for example, the drag on the blade as it travels in the upwind direction is reduced by diverting the flow with a shield. The flow that is not diverted is slowed because the channel becomes wider in the middle. The flow on the opposite side of the rotor (left side in the diagram below) is not manipulated because it is already in the direction of blade velocity, and it therefore already reduces drag. As for the Savonius, I’m not sure if the idea will work, but I’ve drawn my best guess at how to augment the efficiency of the turbine using either one or two shields.

Shielded VAWT

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 21, 2009

VAWT Forest

Many tall slender VAWT rotors are optimally dispersed and mechanically linked to drive a single generator.

Savonius Forest

Walmart Rooftop VAWT Forest

A weather protection shroud (not shown above) runs along the same path as the chain and protects components from rain and other weather. It may also be desirable to explore the option of using a rotating drive shaft to transmit power from turbine to turbine, and finally to the generator. I won’t draw this option, because I’ve already drawn it for one of the variations below.

In the following embodiment, rotors form a wall along the four sides of the roof. A tarp that is supported by a lightweight metal frame runs along each of the four sides of the roof and beneath the rotors. The tarp minimizes turbulence.

Walmart Rooftop VAWT Wall

Variable Scale Deployment – Rotors Suspended From Tubes

This embodiment is suitable both for utility scale deployment, such as a large VAWT Forest suspended over a cornfield, as well as for small scale deployment, such as a rooftop turbine for a residence.

One Row of VAWT Forest Suspended From Tubes

In this variation, rotors are suspended from a bunch of tube segments. The tubes are connected by flexible joints that allow them to approximate the troposkein shape of a cable. Suspended VAWT rotors drive a chain that runs inside the tubes along their longitudinal dimension. A universal joint connects the turbine rotor shaft to a second shaft above the turbine rotor. The weight of the turbine rotor keeps its shaft approximately vertical. However, in high winds the lower end of the rotor shaft can swing in the downwind direction, thus regulating power output and thrust load on the supporting tubes. The yielding rotor shaft also provides a low drag profile storm wind shut down mechanism. The drive chain bears only a relatively low torque load, since tubes carry the gravity load, and since the diameter of the turbine rotor is relatively small (so that the rotor turns at relatively high rpm). Whatever the chain load, it acts to lift the row of turbines up against the force of gravity, and it also cancels some of the gravity load supported by the tubes. Only a single chain runs down one row of turbines because the return path for the chain is through the next higher level of turbines:

Path of Drive Chain, VAWT Rotors Suspended From Tubes

Rotors Suspended From Cables, Counter-Rotating Torque Tubes

VAWT Forest With Counter-Rotating Drive

VAWT Forest With Counter-Rotating Drive (Zoomed In View)

The universal joints not only allow for transferring mechanical power to a slightly different axis, they also permit the rotor to yield in response to wind gusts, and to assume a nearly horizontal orientation when the machine is shut down for storm winds. Note that if the wind direction is at a right angle to the cable, then the cable will twist in response to rotor thrust. This does not present a problem because the orientation of the torque tubes is fixed with respect to the cable, and so the torque tubes move along with the cable when it twists. The orientation of the top rotor shaft is also fixed with respect to the cable, so it rotates along with the torque tubes when the cable twists.

Reciprocating Drive

It is also possible to use a reciprocating drive for all of these machines. In this case, a tube is pushed and pulled by a crankshaft. Perhaps the simplest (and least expensive) option would have the crankshaft driving a cable. I will add some drawings of these options if I have more time later.

For more related discussion, see VAWT Wall.

VAWT Wall

A great number of very tall and very slender VAWT rotors are arranged into a circular wall. All rotors are mechanically linked to a common drive mechanism (chain and sprocket?) so that all drive a single generator:

Savonius Wall

Alternatively, the wall is separated into (say) 30 degree arc segments. All of the rotors that are contained in a given 30 degree arc are mechanically linked to drive a single generator, but each arc drives a separate generator. This way the arcs that are largely parallel to wind velocity will not drag down the arcs that are largely orthogonal to wind velocity. (And those arcs that are largely parallel to wind velocity may still produce a small amount of power.)

Of course, the same idea may be applied to any type of tall slender vertical axis wind turbine.

Suppose 2 bladed H rotors or 2 bladed Darrieus rotors are used. In this case the rotational angle of each rotor may be phase shifted somewhat with respect to its neighbors, and the power output of the machine will be very smooth.

Of course, it isn’t necessary for the wall to be circular in shape. I’m guessing that a circular wall would produce the most energy and the highest capacity factor at sites that have completely unpredictable wind directions. But if a site has a somewhat predictable wind direction, then the wall can definately be shaped to take advantage of the prevailing wind direction. Also, the wall may assume a non-circular shape in order to make its way around some obstruction like a barn or something like that.

Note also that the smaller the rotor diameter, the higher the rotor rpm! This characteristic might allow for eliminating the gearbox (or at least for reducing the speed change required, and thereby increasing the efficiency of mechanical power transmission.)

Seems like this machine may turn out to be suitable for almost any application you can think of – from small to gigantic utility scale wind turbines! Imagine a wall of these rotors on top of a Walmart. The rotors could be small diameter, fairly tall, and made of plastic. Even if a rotor flies apart it shouldn’t create a hazard since its only light weight plastic. And it certainly seems like this idea would be just absolutely perfect for low cost, clean energy in the third world! Imagine a machine like this driving the low-tech water transport pump I posted earlier:

Dirt Cheap Ultra-Simple Efficient Third World Water Transport Pump

Muti-Speed Transmission

Yawing VAWT Wall

This machine doesn’t need a yaw drive, as its yaw angle is self regulating:

Downwind Yawing Savonius Wall

April 17, 2009

Lifting Savonius

Lifting Savonius

April 10, 2009

Variable Pitch Savonius Turbine

Variable Pitch Savonius with Aerodynamically Adjusting Vanes

This post describes a modified Savonius rotor that might be useful for low power applications in undeveloped areas with no power grid. We’ve all seen homemade Savonius rotors built by sawing an empty barrel in half. Let’s begin by imagining just such a barrel, but instead of sawing it in half, we cut a large slot into one of its sides:

Slot Cut In Side of Barrel

Now we cut an identical slot into the opposite side of the barrel. Next, the slots are adorned with two nylon vanes. These vanes can bow like the sail of a sailboat. They can bow in towards the axis of rotation (so that they are actually inside the barrel), or they can bow out away from the axis of rotation:

Aerial View, Variable Pitch Savonius

Downwind View, Variable Pitch Savonius

Instead of nylon vanes, the metal that was removed to make the slots in the side of the barrel can be made into little swinging doors on hinges.

Comparing the Variable Pitch Savonius with the Standard Savonius, notice that the vanes of the Variable Pitch Savonius cannot impede the motion of the rotor. The same cannot be said of the Standard Savonius. For this reason, the Variable Pitch Savonius might turn out to be more efficient than the Standard Savonius. Note that if the Variable Pitch Savonius is attached to a Darrieus rotor in order to make the Darrieus self-starting, then once started, the Variable Pitch Savonius rotor will not load down the Darrieus rotor. (This is so because the vanes of the Variable Pitch Savonius cannot impede the motion of the rotor.)

Standard Savonius and Variable Pitch Savonius Compared

An Alternative Approach

Variable Pitch Savonius, An Alternative Design

Each of the arc shaped vanes in the diagram above are rotated as far as they are able to go in normal wind conditions before hitting stops that limit their further rotation. Two of the vanes are rotated in toward the axis of rotation (red “X”), and two are rotated away from the axis of rotation. In high winds, the vanes are able to rotate beyond the angle permitted by the stops. This happens as the restraining forces of springs (not shown above) are overpowered. In this case, the rotor assumes a low drag configuration approximately as depicted in the following diagram:

Variable Pitch Savonius, An Alternative Design, High-Wind Low-Drag-Profile Mode

Alternatively, maybe springs could draw the vanes toward their nominal position (which is where every point on the vane is equidistant from the rotor axis of rotation). In this case, as the wind blows harder and harder, the vanes sweep a larger and larger angle. Finally a wind speed is reached where the rotor shuts down as depicted above.

The arc shaped vanes might be made of plastic, kind of like a whiffle-ball bat. In this case, they might be so light in weight that it wouldn’t be necessary to counterbalance them to prevent centrifugal force from causing them to always be swung out away from the axis of rotation. Also, the arc shaped vanes should have rounded ends like the leading edge of an airfoil. Hopefully, this would reduce the amount of turbulence generated by the interaction of the arcs and the wind.

Vane of Variable Pitch Savonius Has Rounded Ends (Aerial View of Vane)

Variable Pitch Savonius, Alternative Design, On Guyed Tower

I haven’t had nearly enough time to think about the Variable Pitch Savonius, especially how it might be configured on a guyed tower, and how the various levels of rotors would interface with the electric generator. Hopefully I’ll have time later to come back and add more to this post.

When stacking multiple levels of VAWT rotors, it might be good to keep in mind the issues discussed in the Helically Stacked Darrieus or Savonius Rotor.

Another alternative would have a rotor with many short pivoting arcs like the two depicted above. Also, airfoils could replace the arcs:

Self-Starting Variable Pitch Darrieus

It seems intuitive that a drag type rotor needs more solidity, because it is less able to act on air from a distance. But an inexpensive turbine designed for rural or third world application needs to be reliably self-starting. The last diagram above shows a rotor that uses airfoils. Because this rotor uses lift, it needs less solidity, and some of the airfoils could be eliminated from this design. Unfortunately, eliminating some of the airfoils would seem to reduce startup torque. But here’s an idea to get around this problem. Here we allow the airfoils to rotate through a very large angle when the rotor isn’t turning. This produces a lot of startup torque. As the rotor spins faster and faster, the airfoils are more and more biased toward their nominal (zero pitch) orientation. This is realized using a flyweight. Because this idea is very three dimensional, and I’m a terrible artist, I couldn’t do it justice in a diagram. But I’ll go ahead and post what I’ve got, and try to fill in the rest with a written explanation:

Self-Starting Centrifugally Regulated Variable Pitch DarrieusThe radial arm that supports the airfoil should be on top of and on bottom of the airfoil in the diagram above. But this would block your view of the centrifugal pitch regulating mechanism, so I tried to draw a see-through ghost arm instead. A cable attaches the trailing edge of the airfoil to a centrifugal flyweight. When the rotor is stationary, the wind can easily push the airfoil away from its nominal zero pitch orientation because it has only to lift the flyweight (which will be hanging down toward the ground when the rotor is stationary). As the rotor spins faster and faster, the trailing edge of the airfoil is pulled towards its nominal zero-pitch orientation with greater and greater force. (The part of the arm that supports and routes the cable is ridiculous in the diagram above. In an actual design, it would probably extend from the axis of rotation to the trailing edge of the airfoil along the chord line. But I had to draw it this way in order for all the parts to be visible.)

Check This Out!

Just found a similar rotor on the web that’s pretty cool:

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