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!


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 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.

Horizontal Savonius Circular Wind Dam

Horizontal Savonius Circular Wind Dam

April 24, 2009

Airborne Savonius

Filed under: Airborne Wind Turbine, Savonius Wind Turbine — Salient White Elephant @ 8:37 am

Three giant helium filled balloons are shaped like the “blades” of a Savonius turbine. The balloons float up in the sky, and transmit power to the ground through a rotating drive shaft or a rotating cable.

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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