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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How I Invent Wind Turbines

Filed under: creativity, inventing — Tags: , , — Salient White Elephant @ 10:51 pm

Idea #1) Cast Your Fate the Wind

If you set out to invent a better wind turbine, and you fail, have you failed? What if there’s no such thing as a better wind turbine? What if the best wind turbine that could possibly be invented has already been invented? In this case, you set out to answer a question that had no answer, and guess what… you didn’t find an answer. Inventors don’t have crystal balls. 9 times out of 10 there’s no way to know in advance whether the dream machine you seek exists in this universe. If it doesn’t exist, then you shouldn’t judge yourself a failed inventor for not finding it. That would be like criticizing yourself for not finding a hundred dollar bill in an empty box.

The act of inventing is an act of risk. I suggest you realize at the outset that what you seek may not exist, and all of your blood, sweat, and tears could amount to absolutely nothing.

Of course, if inventing is a labor of love, then inventing for the sake of inventing can be a very rewarding experience. Sometimes the love runs deep enough to kindle a desire to put your ideas into the public domain. Who knows… you might leave the world a better place, or simply make it more beautiful and interesting. Just as the song of the robin makes the world infinitely more intriguing, a bizarre, cool, or sexy invention can entertain, amuse, and educate, even if it is never actually built. Heck, one of my own favorite inventions was a continuously variable transmission that didn’t even work. (It turned out to be incapable of transmitting torque to the output shaft.) To this day I maintain that one the most stoopernamous qualities of the human race is the way it insists on turning its back on perfectly good inventions simply because they don’t work.

Idea #2) Role Reversal

I had some friends in the countryside of Kentucky that liked to carve wind turbines from Coke bottles while sipping an ice cold beer on the back porch and telling about the 400 pound fish they caught and almost wrestled to the shore before being knocked cold by a swash of his tail fin. This is the type of bottle they’d use (one of the big ones):

Coke Bottle

Next, they’d use a razor blade to make long vertical cuts all around the circumference of the bottle:

Coke Bottle with Vertical Cuts In Body

Next, they would twist each “panel” existing between each vertical cut. Each panel would be twisted about 45 degrees in the same direction (either clockwise or counterclockwise). Now an aerial view of the bottle looked something like this:

Aerial View of Coke Bottle with Cut and Twisted Panels

Finally, they’d run a copper wire right down the longitudinal axis of the bottle. Then they suspended the bottle between two limbs of a tree so that it could spin about a vertical axis:

Coke Bottle Spins About  Supporting Vertical Wire

These little devices were amazing because they would spin so fast. I couldn’t help being fascinated by them. They seemed to be spinning faster than the wind. Of course, given that they are “drag” devices, I knew that they couldn’t possibly be spinning faster than the wind. And I knew that they were only curiosities because, as any educated wind turbine engineer knows, drag devices are “inferior” to lifting turbines.

However, I ultimately derived some benefit from my fascination with this “Coke Bottle Turbine”, because I used it in an invention trick I like to call “Role Reversal”. The result was a completely new type of wind turbine! You may recognize this machine from earlier blog posts:

Circular Wind Dam, Rotated Energy Exchange Variation

Why do I call this “Role Reversal”? Because in the Coke Bottle Turbine, loosely speaking, the role of the panels is to spin. But in the Circular Wind Dam, the role of the panels (now brick walls) has been changed so that they are one of the stationary elements. They are used only to “collect” the wind and “direct” it towards the things that actually do spin.

As you can see, role reversal is a sloppy, loosely defined creative trick. It is completely unlike the formulaic approach to problem solving engineers become accustomed to after years and years of training. But I think inventing works best when you have a command of both formulaic discipline as well as the types of thinking that might be more closely associated with art than with science and technology.

Another example of role reversal? How about taking the torque from the high speed blade tip instead of from the low speed main turbine shaft? Here are two earlier posts that play with this idea: VAWT variation, HAWT variation.

Advantages of Role Reversal

One thing I really like about the role reversal idea is that it generates relevant ideas. The little bit I’ve read about brainstorming or creative thinking techniques seems to mostly involve the generation of random ideas, or ideas that are nearly random. But consider the Circular Wind Dam invention above. It was derived by redefining the role of the panels of the Coke Bottle Turbine. You can see that it is highly probable that the shape of the Coke Bottle Turbine panels may have application for other wind turbine designs. This is true because the Coke Bottle Turbine panels aren’t just random objects – they are objects that are designed to interact with the motion of the wind. So the probability that they may successfully play a different role in a new type of wind turbine is much higher than if I had simply chosen some shape at random, and then asked how that shape might be used to make a new kind of wind turbine.

Idea #3) Describe the Obvious, Then Challenge Your Description

Write down how your wind turbine works, then simply challenge each of the statements in your description. Start off simple. If you don’t get any good ideas by challenging a simple description, just repeat the process by writing another description with a little more detail. Then just keep getting more and more detailed until you either come up with something good or decide you’re on a dead-end road.

For example, here’s a really really simple explanation of how a vertical axis wind turbine works: “A few blades are attached to a vertical tower that is situated at the center of the blades. The blades and tower rotate as a unit”. You can hardly get the words of this ridiculously simple description onto the page before the question arises: “does the tower have to be at the center of the blades?” Clearly it does not:

20 MW Direct Drive Darrieus Wind Turbine

Idea #4) Borrow from Distantly Related Disciplines

There are lots of little plastic “wind turbines” on YouTube. Many are, like the Coke Bottle Turbine pictured above, carved from plastic toys and bottles and such. These are curiosities – little plastic gadgets that spin in the wind for decoration. Wind turbines are among the most expensive, heaviest machines on earth. What could they possibly have in common with little plastic toys and gizmos made for half a cent apiece in Korea? And yet they do have something in common. Little plastic things often use the minimum amount of plastic possible, yet have the need to be mechanically stiff.

I saw a striking example of this yesterday as I sipped an ice cold Canadian Molson beer. It was a large size, fat can of beer, and it looked like this:

Canadian Molson Beer Can Top

I didn’t cut the can open to see if the metal was any thicker at the part with ridges. Furthermore, I’m sure the ridged area derived much of its stiffness from the stiffer, thicker circle of metal at the very top of the can. But wouldn’t it at least be worth a second or two to stop and ask whether cost and weight could be removed from a wind turbine tower or blade spar through the use of a similar design?

Wind Turbine Tower with Ridges

Perhaps even the skin of the airfoil could be designed in this way. As a matter of fact, I’ve been seeing web pages about how they are adapting the hydrodynamics of a whale’s fin for the wind turbine application. (It has a vaguely similar ridged shape.) Having made the beer can observation, however, I almost wonder if a whale’s fin is shaped the way it is as much for the resulting mechanical properties as for the hydrodynamic properties.

Idea #5) Focus on Emerging Technologies

I worked in the wind industry about 10 years ago. At that time the field of power electronics was exploding. Wind turbine technology made great strides during those years simply by incorporating the new power electronic devices that were being invented. This is the easiest and smartest way to improve technology. It’s like using a metal detector to comb a beach that has never been combed before by any other person. Naturally, your chances of finding treasure here are far far greater than combing a beach that has already been examined by thousands of talented people.

So why did a smart guy like me spend his time searching for new wind turbine configurations when brilliant minds have already been “combing this beach” for centuries? Well, there are a few answers. For one thing, I don’t work in the wind industry anymore, and for another, I don’t have access to inside information about relevant emerging technologies (like materials science?). But even if you find yourself smack in the middle of the hottest emerging technologies, I think this blog can still be useful to you. This is true because there’s no reason why you can’t apply some of the “How I Invent Wind Turbines” tricks explained here to the adaptation and incorporation of the emerging technologies.

There is also the “second wave” of new technology incorporation to consider. For example, after the adaptation and integration of power electronics that happened in wind 10 years ago, each turbine was left with its own power electronic controller. I don’t know where the industry stands on this issue today, but suppose that it’s still the case that each turbine has its own power electronics. You might choose to tackle a problem that is a little bit more like combing that beach a second time with your metal detector. You may attempt to develop a way to have only a single power electronic controller synthesize clean 50 or 60 Hz power for the entire wind farm, thus sparing each wind turbine from having to have its own separate power electronic controller. Each time you run your metal detector over that beach, you will have to use more tricks and ingenuity to come up with a viable answer, and that is one of the reasons why I am sharing the tricks that work for me.

Idea #6) Thinking WAY Outside the Box

Inventing is a social act. Most people are embarrassed by thinking outside of the box. Why? Fear of making mistakes? Fear of being laughed at? I don’t know. But I can imagine that if thinking outside of the box is embarrassing, then thinking way outside the box must be unbearable. And why would anyone want to come up with ridiculous ideas anyway?

Ridiculous ideas are like stones in a river. You stand on one side of the river, squarely inside the box, longing to be the genius that can cross to that oh-so-cool and sexy unconventional solution that lies on the other side of the river. You can’t walk on water, but sometimes you can step on the stones that protrude from the water and walk all the way across to the other side. The stones are the ridiculous ideas. The stones are often the ideas that are so far out of the box that you would never want to admit to anyone that you could have thought of such a stupid idea.

In my own inventing, I have found that sometimes the path illustrated below is impossible for me to follow:

The Impossible Path

But sometimes I have been able to reach the cool solution by following a path like this:

The Unlikely But Possible Path

Instinctively, I want to say that this approach works well for intractable, practically unsolvable problems – problems like homelessness, pollution, or improving the age-old three-blades-on-a-tower wind turbine design. Don’t get me wrong. I’m not saying I’ve succeeded with this approach. I don’t know if any of the wind turbine designs posted here are even worth the time it would take to develop a computer simulation of their performance. I’m only sharing with you the Salient White Elephant experience.

Idea #7) Ridiculous Ideas and the Argument of Extremes

In addition to the benefits of thinking way outside the box, there is another reason for entertaining ridiculous ideas. I call this technique the argument of extremes. The argument of extremes sometimes lets us use our intuition to answer a question that would normally require a more rigorous mathematical analysis. The best way to teach the argument of extremes technique is by example… so here we go.

Everybody knows an 18 wheeler (tractor trailer truck) needs more room to go around curves. Let’s suppose you’re learning to drive an 18 wheeler, and you want to understand this phenomenon. One of the first things you will learn is that the driver slides the wheels at the back end of the trailer forward or backwards to balance the weight of the stuff in the trailer:

Wheels of Trailer Can Be Slid Forward or Backward

So the question is – is it easier (and less dangerous) to go around a turn when the wheels are slid forward or backwards? We can answer this question by visualizing an argument of extremes. This means we imagine the two opposite extremes – wheels ridiculously far forward, and wheels ridiculously far backward. So we imagine a ridiculous tractor trailer. The tractor is normally sized, but the trailer is a whole block long! The wheels on this trailer can slide all the way forwards to the front of the trailer, and all the way backwards to the back of the trailer:

Wheels of Trailer Slid Backward

Wheels of Trailer Slid Forward

The two opposite extremes pictured above show that it can be difficult to make a turn in a tractor trailer truck regardless of where the wheels are. Both extremes are potentially hazardous.

So imagining extreme variations of our ideas can shed light how the ideas work, and often the exercise sharpens our intuition and allows us to sidestep mathematics.

Here’s another good example. The laws of fluid mechanics say that a wind turbine with a conically shaped shroud (flow concentrator or flow diffuser) has only limited value because there is a limit on the benefits of making the shroud larger and larger. This is true because you can only squeeze a limited amount of “extra” wind through the hole at the smaller end of the cone. Do you believe this? Is it intuitive? I believe it, and I’ll tell you why. Imagine a giant cone; larger end opening toward the wind, and the vertex of the cone on the downwind side (a “flow concentrator”). The vertex of the cone doesn’t have a hole, but we’ll use a sewing needle to puncture it so that it has just a tiny little hole. Do you think all of the wind in the approaching streamtube that is the size of the large opening will be forced through that tiny hole at the other end? No. At this extreme, our intuition kicks in and we realize that 99.9% of the approaching wind will veer around the cone altogether, almost as if it didn’t have a smaller hole. If this were not so, you could make a cone out of porous paper (with no hole at the vertex), hold it up to the wind with the vertex downwind, and feel no resistance to the approaching wind. Imagining these ridiculous extremes helps us to get an intuitive feeling of the effects of the wind’s viscosity.

A word of advice – the argument of extremes can be difficult to apply. It takes a lot of practice to get good at it. But in my experience, the effort has been well rewarded, as you can sometimes gain a very powerful perspective on a very difficult problem if you can only correctly apply the argument of extremes.

Idea #8) Reject Bad Ideas to Make Room for Good Ideas, Reject Good Ideas to Make Room for Genius

The Bible says that “there is nothing new under the sun”. This may be true, but God has filled the world with so many mysteries that you haven’t seen more than about 1% of them. A good inventor is like a newborn baby who is thrilled in knowing that there is a whole universe of things out there that he has yet to witness or understand. The upshot of this attitude is that there is always a new and better way to do something.

If you have a bad invention, and you want a good one, then you have to reject the bad idea. What this means to me is simply that you have to be dissatisfied with the bad idea, and go on inventing new and better wind turbines. Pretty soon you’ll have a good design. But don’t stop there – be dissatisfied with the good design, keep on inventing, and pretty soon you’ll have an even better one!

Part of the process I’m describing involves evaluating your inventions. Is an invention bad, good, and if it’s good, how good is it? Comparing two inventions, which one is better? Most technical people know how to evaluate designs, so I won’t address this subject except to say that sometimes we are guilty of omitting feelings from the evaluation. Gut instinct is valuable. Maybe it looks good on paper, but it just doesn’t feel right. Ask how the frontal lobotomy ever became a socially accepted phenomenon? Yes, maybe there were philosophical or technical arguments that cast the practice into a favorable light, but how could anyone have ever felt good about it? I suspect that if feelings had been taken into consideration, someone would have concluded that as much as the scientific community genuinely wanted to help mentally ill people, they just hadn’t figured out how to go about that helping yet. One of the most difficult aspects of being an inventor is the nearly daily diet of sour stomachs you must suffer through on your journey to discover something that feels right. But don’t despair. If you can reject an idea that doesn’t feel good, then you’ll eventually get to experience that wonderful feeling of knowing you’ve hit on something that has genuine value. And if you can go on suffering the embarrassment of bad inventions even after you have a good one, you may just turn out to be one of those rarely fortunate individuals who, at the least expected moment, is touched by an angel. Then you will stare in wonder at the fruit of your labor, knowing that after all of your searching, all of your suffering, you’ve discovered a design that could only be called genius.

So where does it end? When is a design good enough? Well… you may have plenty of designs that are not just good enough, but that are excellent, and that you should be proud of. But the quality of your designs is irrelevant. Inventors invent. When do you stop trying to design a better wind turbine? Never. Why would you stop looking when there is always a cooler wind machine out there? Why would you end your fascinating journey when there are are more new wind turbines to be discovered than there are stars in the sky?

Idea #9) Teamwork is More Powerful Than Genius

It is unfortunate that the patent system has spawned such a secretive work ethic. Teamwork and collaboration are very very powerful ways to increase both the speed with which you can come up with creative ideas, as well as the scope of those ideas. Consider how powerful it is to have Wikipedia at your fingertips. Isn’t it like having a professor by your side who seems to know just about everything, and who shares information freely without worrying about patents? I can’t tell you how much faster I work when I have access to Wikipedia.

Unfortunately, about the only place in private industry where you see teams of people solving problems is in the open source software movement. So if you attempt to find ways to get non-software people to play as a team, be ready for a challenge! That secretive work ethic has been in place for a long long time, and people will have a hard time adapting to a different way of doing things. You’ll probably have to come up with some kind of incentive for being a team player.

Idea #10) Read About Other Inventions

It never fails – as soon as you read about another invention or, better yet, see a picture of it, you’ll have several new ideas of your own. The best of all is, of course, to be able to witness the invention in person – to touch it, to watch it work, to get a feel for sizes, weights, and other important qualities. So don’t remain isolated for too long if you can help it. If you remain isolated, you’ll probably just end up inventing the same old ideas over and over. (Not to mention you will too frequently reinvent things that have already been invented.) If you can’t find an invention that relates to your field (for example, if you’ve already read about all the wind turbine inventions you can find), then find a related field and read about those inventions. Even unrelated fields can spark ideas that are useful to you. The point is that you want to see creativity in action. To a certain extent, you will absorb that jazzy way that inventors think just by seeing the innovative way they sidestepped a problem and found a solution.

Idea #11) Reinvent the Wheel

Don’t ever be discouraged if you discover that you invented something that has already been invented. Remind yourself that it takes just as much creativity for the second person to invent the invention as it took for the first person to invent it. Furthermore, you’ll never understand any technology as well as a technology you invented yourself, even if you were the second to invent it. So by reinventing the wheel you are learning to thoroughly understand your wheel, and this understanding will help you come up with more cool ideas in the future.

Also, if you are inventing for the sake of making the world a better place, then the “race” (to be the first) isn’t important. The only thing that is important is to come up with a good solid solution for the problem. I hope wind technology will one day produce the cheapest electricity in the world, regardless of who designs the technology. We need inventions like that, if for no other reason to encourage others who want to help make a better world.

To Be Continued… More Ideas on How to Invent

I hope to have more chances to post my tricks for inventing new wind turbine designs. I’ve got lots and lots of tricks to tell you about, but unfortunately it’s really hard for me to get time to post to this blog anymore. We’ll just have to see what happens…

Energy Storage for Offshore Wind Turbines

Offshore Turbine with Energy Storage

When the wind turbine is producing power that isn’t being used, the energy is used to drive the reversible hydro turbine in the direction that evacuates the storage tank. Later, when the power is needed on shore, water is allowed to refill the evacuated tank. The process of refilling the tank drives the hyrdo turbine in the reverse direction to produce electricity.

Instead of having one tank per turbine, maybe a long underwater hallway passes by each wind turbine, and then goes to the shore. The wind turbines pump water out of the hallway, and water can refill the hallway by flowing through the hydro turbines near the shore.

One problem with this idea is that you want to put wind turbines in shallow water, but you want to put this energy storage device in deep water. The Hoover Dam is 220 meters high – ten times higher than the depth to which offshore turbines are currently built. But of course, the storage chamber doesn’t have to be directly beneath the turbines. Think of the incredibly high energy density you could achieve if the storage tank were very very deep! You’d be moving the water against such a large head that you wouldn’t have to move much water, and the size of the storage chamber could be reduced. What if you could find a place with a depth of 20 meters for the wind turbines, and a nearby drop-off that led to deep water where the storage chamber would be placed? Doesn’t seem so improbable does it? Aren’t there lots of “cliffs” on the ocean floor?

No expensive, intrusive reservoirs are required for this system. The water simply goes into the ocean when it exits the storage tank, and returns from the ocean when producing power. Also note that the water storage tank can be built beneath the ocean floor in order to use less concrete. Since it’s an offshore turbine, the turbine can be close to its associated energy storage mechanism (rather than having to transmit the power a long ways to the storage facility). The energy storage mechanism is harmless to ocean wildlife, and does not cause any visual pollution.

The Hoover Dam is just 220 meters high, and it produces a slapsnoggeling 2 GW. But there are places where the ocean is easily 20 times deeper than the Hoover Dam! (Even the Great Slave Lake reaches three times this depth!) Can you imagine the energy density that could be acheived with this form of storage! With such a favorable energy density, it may be worthwhile to go to a lot of extra expense to transmit power to and from these places, and to figure out how to actually build something at that depth. (Maybe much could be built on the surface, and then sunk to the bottom. Maybe some stuff could even be raised from the bottom to the surface for maintenance and repair!) If these problems could be solved, it may prove cost effective to store energy from many sources – not just wind turbines.

Deep Water Variation

The deepest part of Lake Superior is 400 meters (about twice as deep as the Hoover Dam is high). Imagine allowing a gigantic plastic chamber to fill with water, and then sink to this deepest spot. The chamber does not need to withstand any pressure differential because it is filled with water (and vented to the outside water as it sinks). Once on bottom, robotic machines dig up the material at the bottom of the lake and pile it on top of the plastic chamber. They keep piling stuff on top of the chamber until they have essentially created a “false bottom”. In other words, the chamber is nothing but a mold for the shape of an underground room at the bottom of Lake Superior. Finally, concrete tubes that have the reversable water turbines inside are sunk to the bottom, and the robotic machinery then manipulates these tubes so that they connect the underground room with the lake above. Voila! Deep water high density energy storage!!

Compressed Air Variation

As usual, I am running my mouth in this post about technology that I know little or nothing about. It occurs to me that a “reversable water turbine” may be a bigger deal than I think. Or perhaps the efficiency is high in one direction, but not in the other. Or perhaps the efficiency of an air compressor would be higher at those astronomical pressures. In any of these cases, the following design may be considered. Note that there are 4 possibilities with this design:

  1. air turbine compresses air to store energy, water flows through water turbine when refilling tank to harvest the stored energy
  2. water turbine removes water from the chamber to store energy, air turbine harvest energy of escaping air when water flows back in to the tank
  3. air turbine alone is used when storing or harvesting stored energy
  4. water turbine alone is used when storing or harvesting energy (as in original diagram above)

Lake-Bottom Energy Storage with Both Air and Water Turbines

Underground Tunnel Variation

Another twist similar to the one just described would bore a tunnel from the shore to some point beneath the water. Then, a large “underwater room” is built just above the end of the tunnel as described previously (by sinking a giant plastic bottle and then covering it up with mud). Now the tunnel is connected to the underwater room, the underwater room is vented to the lake water through a concrete tube that has a water turbine, and the air turbine is placed near the shore at the mouth of the tunnel that runs underneath the lake.

Mechanical Drive Variation

An offshore wind turbine has a direct mechanical drive that actuates a water pump. The water pump acts to evacuate the storage chamber at the base of the turbine. Electricity is involved only when the chamber is refilled, and the system is sending electrical power to the shore for consumption. A little thought will show that the turbine can be producing power and consumers can be using the power, both at the same time. All that is required is that one system doesn’t “outrun” the other, so that the storage tank either gets completely filled with water or completely evacuated. If the chamber is completely filled with water, then no electrical power may be produced. If the chamber is completely evacuated, then the turbine is no longer able to store power, and must be shut down.

Energy Density

Well, maybe I’m getting excited over nothing. It’s been so long since I crunched numbers, I don’t trust my numbers anymore. But I banged out a few quick equations to try to figure the energy density at the depth that a sperm whale can reach, which is 7,400 feet. The result, if correct, says that an evacuated chamber at a depth of 7,400 feet has an energy density of 23 kilojoules/liter. By contrast, according to Wikipedia, the energy density of a lead-acid battery is 360 kilojoules/liter. So even a stupid lead-acid battery has ten times the energy density of even that ridiculously deep chamber. Oh well… you just can’t win at this invention game, can you? Back to the drawing board.

In case you want to double check my numbers, here’s a rough idea of what I did. It’s 223 atmospheres at 7,400 feet of depth, which is 22.6 MegaNewtons/cubic meter. Because work is equal to force times distance, this is the same as saying that it’s 22.6 Megajoules/cubic meter, or just 23 kilojoules/liter. I got the energy density of other materials from the Wikipedia article on energy density.

Crash and burn folks – that’s my middle name. Ol’ Salient “Crash ‘n Burn” White Elephant, does it again. Why couldn’t I have been born an accountant?

*****

Well, this is later after I wrote the above, and I was reading about compressed air energy storage in Wikipedia. It said that first of all, it’s tricky to compress and expand the air, because it heats up and cools down in the process. And secondly, it said “if 1.0 m3 of ambient air is very slowly compressed into a 5-liter bottle at 200 bars (20 MPa), the potential energy stored is 530 kJ (or 0.15 kW·h)“. So this is saying they get 530 kilojoules for a cubic meter while I’m getting 22.6 Megajoules/cubic meter (40 times more), and I don’t have all the thermodynamic challenges that they do. I guess I just don’t have time to sort all this stuff out. But I think this idea will go the way of all the other Salient White Elephant inventions – straight to the wastebasket. That’s my home… the wastebasket. Just dig down beneath the wadded up paper and coffee grounds if you’re ever looking for me… that’s where I’ll be.

This Solution Doesn’t Feel Right

Another of my posts, How I Invent Wind Turbines, explains how I reject bad ideas to make room for good ideas. One of the points made in that post is that sometimes you just have to depend on how something feels, rather than on how it looks on paper. This post is a good example of a solution that just doesn’t feel right, not because the energy density is disappointing, but for another reason. What is that reason? Well… you know… you know… that by the time you could build a 7,400 foot deep energy storage reservoir (if you could ever build such a thing), someone would have invented the high voltage super capacitor, and you’d be left with a White Elephant at the bottom of the ocean… and he wouldn’t even be Salient anymore! (Actually that sounds like a good book title doesn’t it? White Elephant at the Bottom of the Ocean. I’ll have to remember that.)

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?

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