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!

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

jeannie4

I Dream of Genie Wind Dam Construction - 3

Genie

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

Genie

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

Genie
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.

April 24, 2009

Super Honkin’ Counter-Rotating Water Cooler Cones

Tangential velocity is a function of radius. The radius of the vertex of a cone is zero, so this shows that if you get an empty paper cone from the water cooler and roll it across your desk, it will roll around in a circle. This is kind of nice, since a cone seems very close to the ideal flow accelerator. So if we put the vertices of two cones together, so that the open ends of the cones point in opposite directions, then roll the cones, their vertices will stay together, and the cones will “yaw” all the way around through a 360 degree arc and end up back where they started. So we roll the cones around so that one opens up in the direction of the wind and the other opens up in the downwind direction, put a HAWT rotor right in the middle of the two vertices, and we have a very powerful wind machine with all the important components at ground level. The only problem is that the cones smash all the corn in the field as they yaw around. But this is easy to fix. Just fit the mouths of the cones with a rim and the vertices with a rim, then separate the cones by the appropriate distance. The following diagram illustrates the general idea (it’s a terrible drawing… but I’m in a hurry):

Super Honkin' Counter-Rotating Water Cooler Cones

So now if we have two concrete roads, the cones can roll around and not smash all the corn in the field. Interestingly, it seems these shapes might be perfect for rolling around on top of a dome – like an enclosed baseball stadium or something like that.

Yawing Wind Dam

The diagram looks silly, but don’t dismiss this post too quickly – I think this is a terrific idea:

Yawing Wind Dam

There are many variations, but as we explore those variations, keep in mind the salient points of this machine:

  • direct drive
  • not only is the generator at ground level, the turbine rotor is on the ground as well!
  • incredibly scalable
  • low maintenance.

Variations

Suppose we have five towers in the shape of a giant pentagon. Cables run between adjacent towers, and the shroud is attached to those cables. In this case, only the shroud is yawed:

Yawing Wind Dam, Only The Shroud, Turbine, and Generator are Yawed

Or it can look like this:

Aerial View of Yawing Wind Dam Only The Shroud, Turbine, and Generator are Yawed

Instead of making the shroud out of fabric like nylon, it can be solid. It would look kind of like the top half of a radar dish. In this case, it might be supported by a number of lattice structures on wheels.

Single Tall Tower Variation

Yet another variation would use a single very tall guyed tower. Because the bottom of the shroud is like a circular arc that sweeps through 180 degrees, the diameter of the arc at the lower end of the shroud can be made larger than the diameter of the anchor points for the guy wires. A long horizontal tube at the top of the tower supports the top part of the shroud. The turbine rotor and generator are on rails or wheels and trace out a circle as the machine is yawed through 360 degrees.

Alternatively, the guy wires are used not only to support a very tall tower – they also support the shroud. Suppose there are 5 guy wires. A cable connects the 5 guy wires so that an aerial view of it looks like a pentagon. There are several levels of these horizontal pentagonal cables, so that an aerial view of them looks like several pentagons of different sizes. The shroud is connected at each side to each of these cables, and rides these pentagonal cables as it yaws:

Yawing Wind Dam, Single Tower Variation

Tipi Variation

Just like the single tower variation just described, except now the entire surface traced out by the guy wires is covered with fabric. It looks like a giant American Indian tipi. Now all of the fabric that runs the circumference of the tent from an elevation of (say) 20 feet to 30 feet is separated from the rest of the fabric. It looks like a giant pentagonal wedding ring. This ring has two holes cut into opposite sides of it, and a fabric tube connects these two holes. The tube has the turbine rotor inside of it. The tube and the ring yaw, and the rest of the tent is stationary. The turbine is near the tower (or coaxial with the tower) so that it doesn’t have to move much when yawing.

April 23, 2009

Extremely Tall Direct Drive Wind Turbine

No Wind, Extremely Tall Direct Drive Wind Turbine

Aerial View, Extremely Tall Direct Drive Wind Turbine

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

Airborne Wind Dam

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

Wind Turbine with Flow Accelerating Shroud

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

Here’s another variation:

Airborne Wind Dam

Airborne Wind Dam with Lattice Support

Blimp With a Hole Variation

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

Airborne Wind Dam, Cylindrical Hole in Blimp

Skyscraper Variation

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

Lightweight Electrical Components Variation

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

Structural Electrical Cable Variation

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

Aerodynamic Transmission Variation

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

Airborne Wind Dam With Aerodynamic Transmission

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

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

Pressure Differential Aerodynamic Transmission Variation

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

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

Rotating Drive Shaft Variation

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

April 21, 2009

HAWT Wall

Filed under: Horizontal Axis Wind Turbine (HAWT) — Tags: , — Salient White Elephant @ 2:50 pm

HAWT rotors are configured in various ways within a plane, and are mechanically linked to drive the same generator.

HAWT Wall

See VAWT Wall.

Torque-Speed Decoupling HAWT

I don’t have near enough time to do justice to this idea. I’ll just post it in very abbreviated form and leave the rest to your imagination.

Torque-Speed Decoupling HAWT, Downwind View

Torque-Speed Decoupling HAWT, Side View

Torque-Speed Decoupling Mechanism

The chain-like structure that protrudes from the inner perimeter of the rim of the spoked wheel is essentially just a bunch of rollers whose axes are parallel to the rotor axis of rotation. The fact that these engaging mechanisms are rollers (rather than just fixed pegs) permits very efficient transfer of mechanical power from the rotor blade to the chain drive.

Variations

The high speed generator shaft can be attached to a second smaller (aerodynamic) rotor. This permits more efficient conversion of energy flowing through the axial region of the rotor disk, and eliminates the big fat twisted small-radius section of the larger rotor blade.

The chain drive may be replaced with a high-speed rotating shaft whose axis of rotation is coaxial with the longitudinal dimension of the blade (coaxial with the blade spar). The rotating shaft goes down the center of the blade just like the chain drive. A tire at the blade tip engages a ring that looks like a giant washer and that protrudes from the inside of the rim of the spoked wheel. The tire drives the high-speed shaft that goes through the center of the blade. Assuming a 2 bladed turbine, the two shafts will be counterrotating. One of these shafts drives the generator rotor and the other drives the “stator” in the opposite direction. In this design, the generator rotates with the blades and slip rings will be required to transmitt power from the rotating generator.

Yet another variation has the chain drive or high-speed rotating shaft running longitudinally inside the spar of an H-Rotor Darrieus. In this embodiment, either the generator can rotate with the blades and transmitt its power out through slip rings, or else another sprocket near the tower protrudes from the spar and drives a rotating ring which in turn drives a generator that is fixed with respect to the turbine foundation.

April 2, 2009

Transmitting Mechanical Power Down the Tower

Filed under: Horizontal Axis Wind Turbine (HAWT) — Tags: , , , , — Salient White Elephant @ 4:05 pm

I always wondered why nobody ever tried to put a HAWT gearbox and generator on the ground rather than at the top of the tower. I always just assumed that if I were a mechanical engineer, then I’d know that the numbers just don’t work. But then it occurred to me that this is exactly how the Darrieus rotor’s power gets to its gearbox and generator. Of course, only half of the torque comes from the top of the tower, but still… it got me to wondering if it might somehow be feasible to put the HAWT gearbox and generator on the ground. And my elementary school teachers always assured me that there’s no such thing as a stupid question, so…

(bear in mind that these same teachers would always ask me if I wouldn’t like to spend a month of my summer vacation coming in for English grammar tutoring so I could get a hundred points of extra-credit…)

Transmitting Mechanical Power Down the Tower

March 28, 2009

Wind Turbine With Flow Accelerator Beneath Rotor

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

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

March 27, 2009

Wind Turbine With Flow Accelerating Shroud

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

Wind Turbine With Flow Accelerating Shroud

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

Downwind View Wind Turbine With Flow Accelerating Shroud

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

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

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

Giant Spoked Annular Wheel Variation

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

Wind Turbine With Spoked Annular Shroud, Downwind View

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

Wind Turbine With Spoked Annular Shroud, Side View

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

Cross Section of Side View of Fabric Part of Shroud

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

Wind Turbine With Spoked Flow Accelerating Shroud, Deploying the Shroud

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

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

Linear Turbine Variation

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

Shrouded Linear Turbine With Elongated Oblong Track

March 24, 2009

HAWT With No Shaft

HAWT With No Shaft

HAWT With No Shaft, Side View

HAWT With No Shaft

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

Tips of Bowed Blade More Orthogonal to Local Flow

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

HAWT With No Shaft, Highly Scalable Wind Turbine Variation

Radially Displaced HAWT Rotor

Radially Displaced HAWT Rotor, Side View

Radially Displaced HAWT Rotor, Downwind View

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

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

March 20, 2009

Wheel in the Sky

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

Spoked Wheel

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

Ring Generator, Wheel in the Sky

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

Precision Air Gap Variation

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

Wheel in the Sky Ring Generator, Precision Air Gap Variation

Advantages and Disadvantages of Wheel in the Sky

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

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

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

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

March 13, 2009

Counter-Weighted HAWT

Sometimes the simplest ideas are the most effective. What’s wrong with a turbine that has guy wires that attach to the top of the tower and a counter-weighted nacelle?

Counter-Weighted HAWT

One advantage of a three bladed rotor is that it is much quieter than a two bladed rotor. This is true because a three bladed rotor rotates more slowly than a two bladed rotor. But maybe a four bladed rotor could turn more slowly still, and maybe it would be even quieter. We can achieve this with counter-balanced counter-rotating two bladed rotors:

Counter-Weighted Counter-Rotating HAWT

One advantage of this last machine is that the downwind rotor can extract some of the rotational energy that the upwind rotor supplied to the streamtube. It may also be possible for one wind rotor to turn the generator rotor, while the other turns the generator “stator” in the opposite direction. This doubles the effective generator rpm.

March 12, 2009

Extremely Large Horizontal Axis Wind Turbine With Three Rotors and Three Towers

This post describes an idea for an extremely large Horizontal Axis Wind Turbine. The turbine has three towers and three rotors. This idea is similar to the Radially Displaced Darrieus Rotor. (You might want to read that post first.)

This turbine has the same three lattice towers as the Radially Displaced Darrieus Rotor, and it also has a ring on top that can rotate about the center of the structure. In addition to this structure, put a long horizontal tube on top of the ring, and mount three horizontal axis rotors on the tube:

Horizontal Axis Turbine With Three Rotors and Three Towers

Horizontal Axis Wind Turbine With Three Rotors and Three Towers

Now if the three nacelles and their rotors are instead suspended from the horizontal tube on three short vertical tubes, then the force of gravity keeps the rotor disks vertical. If desired, the short vertical tube from which a nacelle and its rotor is suspended may rotate somewhat about the supporting horizontal tube above. This provides a teetering action that helps make to mitigate the fluctuating loads associated with wind gusts.

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