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!

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Stationary Savonius Turbine

Stationary Savonius Turbine

Savonius in a Savonius

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

June 27, 2009

Cable Untwisting System for Small Wind Turbine

Cable Untwisting System for Small Wind Turbine

The diagram shows the turbine yawed to the position where its power cables are completely untwisted. In this case, the cable that untwists the yaw system attaches to its topmost pulley wheel in such a way that it is not wrapped around that topmost pulley wheel at all. (The topmost pulley wheel is the one with the axis of rotation that is coincident with the turbine’s yaw axis). Now as the turbine yaws, it doesn’t matter which direction the turbine yaws in. Whichever way the turbine yaws, it wraps the untwist cable around the topmost pulley wheel, and in so doing it draws the twist sensing component that is attached to the untwist cable (colored purple) up to a higher elevation. When this part of the sensor passes close by the topmost twist sensor component (colored red), the control system knows that the power cables are twisted up. To untwist the turbine, the controller simply turns on the small electric motor at the base of the tower until the cable mounted twist sensor component passes by the lowest red colored twist sensor component, then turns the motor back off. If the system fails for some reason, the result is that the small untwist motor will burn up or blow a fuse – a minor repair indeed. The controller might wait until the wind isn’t blowing before untwisting the power cables.

Sensorless Variation

In this variation, the controller merely untwists the turbine every time the wind speed drops to zero (rotor blades not turning). Some kind of slip clutch mechanism might be provided to keep the untwist motor from burning up if it runs too long. Alternatively, the motor could be turned off whenever the power it draws jumps up by a large value (indicating the turbine has been completely untwisted). Or a simple mechanical switch could be tripped whenever the turbine is completely untwisted.

Manual Variation

A manual version of this device might also work well. In this case, the controller might issue some kind of mechanical or telecommunications signal to let someone know that the turbine needs untwisting.

High Mechanical Efficiency Centrifugally Stable Darrieus Turbine

High Mechanical Efficiency Centrifugally Stable Darrieus Turbine

June 21, 2009

Business Savvy or Sexy Technology?

Filed under: Brash Environmental Commentary, Wind Energy, Wind Power, Wind Turbine — Tags: , , — Salient White Elephant @ 11:40 am

The earlier post, Why Renewables Aren’t Cost Effective, describes how a taking a different approach to the business of wind technology may produce even more attractive results than a dazzling new technology. Let’s look at other ways for using business ideas to improve the profitibility of small wind.

The Problems with Small Wind

There are two problems with small wind – maintenance and financing. Let’s start with maintenance.

Maintenance

Not many home owners want to climb an 80 foot tower to fix a 10 kilowatt wind turbine. To date, the designers and manufacturers of small wind machines have solved this problem by making their machines virtually indestructible. Many have only a few moving parts – the rotor, slip rings, and yaw bearings. But these machines still break. They could even be hit by lightning!

My answer to this problem is to first reduce the cost of the machine by making it more destructible. If the cost is reduced by a sufficient margin, then it will be deployed in larger numbers. If the number of machines in the field reaches a significant threshold, then a business can be developed for maintaining the machines. In other words, opt for a cheap clunky machine rather than an expensive high tech ultra-reliable machine. Now a customer either hires the maintenance company to repair the turbine or exercises warranty privileges. Technicians repairing the machine are experts, and they aren’t afraid of 80 foot towers. In other words, you can spend your money on two different options:

  1. super duper designs with super duper components, or
  2. mediocre designs with mediocre components and a solid company that provides highly qualified service technicians.

The later option makes more sense. Most home owners won’t even consider learning to repair and maintain a wind machine, but they’ll consider an option that’s backed by service contracts and warranties.

Financing

How long does a wind turbine take to pay for itself? Oh man… I don’t even want to know. If you’ve seen this kind of financial analysis, it’s complicated, and I doubt the average home owner can even understand it, much less believe it. But wait a second… if it’s true… if it really is true… that a 10 kilowatt wind turbine for your back yard is a good investment, then why aren’t there companies that bank roll the installation of such machines in exchange for dividing the wealth so created with the homeowner? Just as service technicians know more about repairing wind machines, financial companies know more about financing them.

What Does This Company Look Like?

The small wind machine manufacturer proposed here does not sell wind machines – it sells electricity. And it sells the electricity to the power company, not to the homeowner. In other words, the homeowner has exactly the same relationship with the small wind company that a farmer has with a utility scale wind farm owner/operator. Just as the utility scale wind farm owner/operator pays the farmer a monthly fee for the privilege of using a few hundred square feet of his farmland, the small wind company pays the homeowner a set monthly fee for the privilege of using her home to produce the electricity that is sold to the power company. The home owner sees a “reduction in her electricity bill” equal to the monthly fee she receives from the small wind company. Everything else, the construction, grid connection, maintenance, repair, and financing of the wind machine is the responsibility of the small wind company proposed here. All the homeowner has to do is avoid hitting the base of the tower with her lawnmower!

Negotiating Power Purchase Agreements

Another advantage of the company proposed here is that, provided its revenue is sufficiently large, it enjoys a strong negotiating position with the utility company. Consider this. When a company that owns a wind farm sells electricity to a power company, what happens to all the energy that is lost in transit as the electricity is carried 30 miles to the consumer over high voltage power transmission lines? Well… maybe it’s easier to look at the flip side of that coin. Suppose you install a wind machine in your back yard and run your meter backwards. The power company just saved a bunch of money because little of this energy is lost in transmission, since it is all used either in your own home or at least in your own neighborhood. The power company also saves money in reduced maintenance of high voltage transmission lines, and reduced need for transmission line capacity in the first place. How much of these savings do you think will be reflected in your electricity bill? You guessed it – zero. You just gave the power company a nice birthday present, and every day is their birthday!

The home owner is not in a position to challenge this state of affairs. But the company proposed here that operates tens of thousands of small wind turbines around the province is in a position to negotiate a reward for the benefits they provide… including the benefits of producing electricity at the point of consumption rather than 400 thousand miles away at the other end of a 10 billion dollar 900 thousand volt transmission line.

Why Renewables Aren’t Cost Effective

The last electric bill I got charged me $65 for the luxury of being connected to the electricity grid, and $5.00 for the electricity I used. In other words, if I had conserved all of my electricity, using no electricity at all, then I would have saved only $5.oo! My bill would have been $65 instead of $70! Really makes you just want to go all out to conserve resources and reduce pollution, doesn’t it!?

The logic behind this rate structure is that the utility company must make electricity available to you whether you use it or not. They must guarantee that if you wake up at 3 o’clock in the morning and turn on every electrical gizmo in your house, then the electricity to power these devices will be available to you. That’s what I paid the $65 for. This $65 portion of my bill is appropriately called capacity charge. It varies based on how much capacity I require, as I will explain in a moment.

Two questions immediately come to mind:

  • Does this rate structure encourage waste. Answer: YES!
  • Does this rate structure reflect the utility company’s cost structure? In other words, are 65/70 = 93% of their costs really devoted to the provision of the service, with only 7% of their costs spent of making electricity? Well.. who knows… but does it sound believable to you?

How the Capacity Charge is Calculated

Now let me explain how the $65 is calculated. Basically, they keep a record of the amount of power you draw for 6 months. Then they look at the maximum amount of power you drew in any one minute for that 6 months, and your capacity charge is based on that amount. Let’s say for example that 3 1/2 months ago I turned everything in the house on at the same time and drew 10 kilowatts. And let’s say that this is the most power I drew at one time during the last 6 months. Then my capacity charge, $65, is based on that 10 kilowatts. Now suppose 2 1/2 months elapse, so that the moment when I drew 10 kilowatts is now more than 6 months ago. Now we look back over my history and find that the most power I drew at once during the last 6 months was only 5 kilowatts. Now my capacity payment drops to $65/2 = $32.50.

How to Beat the System

The manufacturers of small wind turbines designed for residential use are always complaining about this rate structure. Strange, huh? These small wind turbines go on dutifully pumping power backwards – into the grid rather than out of the gird – knowing that if there was so much wind as to make your net power consumption zero you would still only save $5!!! No wonder it takes so long for a small wind machine to pay for itself!

And yet the answer is obvious. Get a small wind machine, add a small battery, and use the wind turbine to keep the battery charged. Now design some electronics to detect peak power usage. Now if I wake up at 3 o’clock in the morning and turn everything on in the house, the wind turbine battery suddenly turns on to limit my peak consumption as much as possible. If the system is able to cut my peak consumption from 10 kilowatts to 5 kilowatts during the 5 minutes that I keep everything turned on at 3 am, then in that 5 minutes I just earned $35! Contrast this with the $5 I would have earned had my wind turbine worked hard every minute of the whole month, producing 100% of the electricity I used for that month!

Is a Wind Turbine Even Needed?

Obviously not. Just draw the electricity from an electrical outlet in your wall in order to charge the battery whenever you aren’t using much electricity for anything else. Now when you turn a lot of things on, the electronics that control the battery realize that you are approaching peak power consumption, and they kick the battery on so that it supplies part of the power you need, thereby limiting your peak consumption and its associated capacity charge.

If You’re an Environmentalist – Play It Smart

So if you don’t need a wind turbine, then what does all this have to do with wind energy? Well… if everybody had these battery systems in their homes to level out power consumption, we’d find out real quick whether $5 is really enough to cover the cost of electricity produced. My bet is that you’d see the rate structure change real quick. Once the rate depends more on the actual amount of energy the utility is required to produce, then it becomes more cost effective to install your own wind turbine and run the meter backwards.

Related Technologies

There’s a whole slew of technologies for conserving energy that become obvious when you look at the problem from the perspective of this post. For example, what about a clothes dryer that automatically shuts off anytime peak household consumption exceeds 5 kilowatts, and then turns back on anytime peak consumption dips back down below 5 kilowatts?

The Moral of the Story

The moral of the story is that environmentalism that is based on nothing but complaining is doomed to fail. What we need are jazzy inventors and entrepreneurs who are patient, calculating, and sufficiently intelligent to twist the arm of a greedy industrialist behind his back and inform him of changes to his job description. He needs to know that his duties no longer include destroying the planet and sending other people’s children overseas to die fighting over oil.

Remember – if twisted logic and pretzel laws work for those who oppose efficiency, then they will work for the proponents of sustainability as well.

A Product and Business Based on this Idea

You buy a product that includes electronics that monitor your electricity usage. A continuous record of electricity usage is kept. The system includes a battery that is just large enough to absorb the average amount of power you use in a day from the power grid. The electronics are designed so that the battery draws enough electricity for one day from the power grid between the hours of minimum demand. Let’s say the hours of minimum demand are from 11pm to 5 am. The battery draws enough power for one day’s worth of your electricity consumption, and it draws that power at a steady even rate from 11pm to 5am every evening. Anytime you use electricity in your house, it is drawn from the battery.

Now, to the power company, you are the ideal customer. You never draw anything but a small steady flow of power during the hours of minimum demand (when they’re trying to figure out how to get rid of their excess power anyway). If ever you use more than your average amount of power, the battery system is bypassed and you draw straight from the grid (increasing your electricity bill).

I think this is what they mean by the “smart grid”. (I keep seeing that term on the internet, but I haven’t had a chance to look it up in the dictionary yet.)

June 18, 2009

3 Spoked Wind Dam

3 Spoked Wind Dam

Pictures of Wind Dam

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

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

 

 

outdoor theater near Saskatoon, Saskatchewan that looks like wind dam

 

 

outdoor theater near Saskatoon, Saskatchewan that looks like wind dam

 

 

outdoor theater near Saskatoon, Saskatchewan that looks like wind dam

 

 

outdoor theater near Saskatoon, Saskatchewan that looks like wind dam

 

 

outdoor theater near Saskatoon, Saskatchewan that looks like wind dam

 

 

outdoor theater near Saskatoon, Saskatchewan that looks like wind dam

 

 

outdoor theater near Saskatoon, Saskatchewan that looks like wind dam

June 17, 2009

Rooftop Wind Turbine

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

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

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

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

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

*****

Okay folks, here’s a simple pic:

Residential Rooftop Wind Turbine

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

Residential Rooftop Wind Turbine with Hinged Flow Diffusor

May 19, 2009

I Dream of Genie Wind Dam

I Dream of Genie Wind Dam Construction - 1

I Dream of Genie Wind Dam Construction - 2

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.

Jet Stream Ram Air Wind Turbine

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

Jet Stream Ram Air Wind Turbine

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

Triple Tethered Variation

Jet Stream Ram Air Wind Turbine, Triple Tethered Variation

Multiple Blimps Variation

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

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

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

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

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

Can We Really Reach the Jet Stream?

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

May 10, 2009

CounterRotating Direct Drive Wind Turbine

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

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

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

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

Ring Generator Option

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

SkyScraper with H-Rotors

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

SkyScraper with H-Rotors

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

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

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

Direct Drive Counter-Rotating Cat’s Eye Variation

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

Geodesic Dome Turbine

Start with a Geodesic Dome:

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

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

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

Retrofit Option

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

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

April 29, 2009

Small H Rotors Perimeter Yawing Flow Accelerating Shroud Atop High Guyed Tower

Filed under: Wind Turbine Flow Accelerating Shroud — Tags: , , , — Salient White Elephant @ 10:12 pm

Small H Rotors Perimeter Yawing Flow Accelerating Shroud Atop High Guyed Tower

Small H Rotors Perimeter Yawing Flow Accelerating Shroud Atop High Guyed Tower

Small H Rotors Perimeter Yawing Flow Accelerating Shroud Atop High Guyed Tower

I guess if the shroud were octagonally shaped then that would probably come close enough to an approximate circle to eliminate really counterproductive flow patterns near the corners of the square:

Octagonal Shroud

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 28, 2009

High Speed Centrifugally Stable VAWT

(Note – there are some errors in this post that I haven’t had time to fix yet, but I’m sure that if you know mechanical engineering you can easily correct the errors yourself. I think this idea might have potential once the errors are corrected. Note also that the torque tube will probably remain fixed with respect to the stationary tower rather than rotating around it. Also note that the struts each need to be connected by a vertical lattice (near the stationary tower) to keep them separated… that is, to¬†prevent the load that tends to bend the ends of the struts towards each other from being transferred to the rest of the structure, thereby defeating the fundamental purpose of the idea.)

(Okay, here’s a pic with some errors corrected, but with no explanation:

High Mechanical Efficiency Centrifugally Stable Darrieus Turbine

)

High Speed Centrifugally Stable VAWT, Side View

High Speed Centrifugally Stable VAWT, Aerial View

This is a 3 bladed turbine, but I have drawn only two blades in order to make the illustration easier to understand. And I realize there are a lot of “legitimate” mechanical designs to realize this concept, likely using gears instead of tires and so forth. But I’m not a mechanical engineer, and so I just want to draw something that will give the real designers an idea they can play with.

Because the tower does not rotate, the rotor can be very tall, very slender, and it can spin at high rpm without becoming centrifugally unstable. But can’t the stationary tower can bend just as much as the rotating tower? And if the stationary tower bends, won’t this cause the rotating part of the structure to become centrifugally unstable just as if the tower were rotating? No. To see this, consider what happens when the middle of a rotating tower bows in response to the lifting forces transmitted to the tower from the airfoil by the middle strut. In this case, the middle of the rotating tower bows in the downwind direction, but its rotational axis does not change. Therefore the mass of the rotating tower has been displaced from the rotational axis, and centrifugal force now acts to cause even more bowing, and the rotor has become unstable. But when the middle of the stationary tower bows in the downwind direction, the rotational axis of the middle struts and airfoils moves along with it. And so although the rotor’s axis of rotation is no longer straight, it is at least centrifugally stable.

Another advantage of this design is that the guy wires are not connected to the tower through bearings. This should provide a big reduction in mechanical losses, since the bearings at the top of a traditionally guyed Darrieus bear a very heavy load – the rotor’s overturning moment. Of course, the overturning moment must be supported somewhere by some bearings. This design has bearings inside the rings that the struts attach to. So is there any advantage in this compared to the traditionally guyed Darrieus? I’m not a mechanical engineer, so I don’t know. Maybe there’s no advantage at all, but I’m wondering if the approach here isn’t better because it is easier to influence the bearings at design time. For one thing, you can spread the load over as many bearings as you want, while the traditional design requires two sets of bearings – one at the top of the tower and one at the bottom. For another thing, the guy wires in the traditional design are not only trying to torque the bearings about a horizontal axis, they are also doing this cyclically, from very low torque to very high torque several times a second. Surely this can’t be good. Of course, the present design also places a cyclic load on the bearings – there’s no way to avoid that. But at least it’s a “typical” load in that it doesn’t try to twist the bearings to a new axis. So maybe this is a better approach. It seems to me that mechanical losses will be decreased by eliminating the torquing thing, but again, I don’t really have the background to know if this claim is accurate.

April 27, 2009

Practical Small Scale Airborne Kite Turbine

Practical Small Scale Airborne Kite Turbine

There’s a hole in the middle of the kite that the tube connects to so that the tube can reach the low pressure behind the kite.

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.)

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