Author Topic: Stupid questions about wind  (Read 22383 times)

Offline mangyhyena

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Stupid questions about wind
« on: September 21, 2010, 04:40:44 PM »
Bear with me a for a few lines of text and I'll explain my question better.

A magnifying glass takes all the sunlight from the surface area of the glass and concentrates it into a little beam, which gets intense enough to burn ants to death.  Does wind work the same way?

If you take a funnel, turn the wide end toward the wind, will the air blow harder out of the small end of the funnel?  In other words, can you concentrate or focus the wind?

With the same funnel example, can the wind be turned into mini tornado if the funnel is grooved or shaped correctly?  If that's possible, would a mini tornado be of any use for boosting the output of a windmill?

I've been wondering about this for a while.  Thanks for bearing with me and satisfying my curiosity.

Offline Herbalpagan

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Re: Stupid questions about wind
« Reply #1 on: September 21, 2010, 05:00:57 PM »
good question. I believe that would be a yes...if you hang a flag up in the wind, it will flap and flutter. BUT, if you hang up a wind sock (funnel) it will go out straight and be at least more focused.  I don't know if the wind gets stronger, just more focused, like the sun thru the glass.

Offline Kwitzats

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Re: Stupid questions about wind
« Reply #2 on: September 21, 2010, 05:18:16 PM »
I would think only slight improvement with wind funelling, with greater air presure inside the funell more air tends to go around the whole thing  additionaly without sophisticated modelling of the air flow there would be anomolus eddies and whatnot that restrict strict redirection of airflow.....then again i have no idea what im talking about so try it.

it seems to me that there are easier ways to capture more air like more blades(even if this resists axis movment and startup speed) or longer ones, materials permitting.
still no idea fluid dynamics are way to hard for my meager brain

Offline mangyhyena

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Re: Stupid questions about wind
« Reply #3 on: September 21, 2010, 06:07:50 PM »
This thread is just about my stupid curiosity.  I've seen tornadoes on television and there was a lot of power in them.  It just seemed to me that if there were some way to replicate that on a much smaller scale, there might be a potential for energy production above what the wind, before swirling it, would normally yield.  I could easily be way off base, here.  And I'm not looking to replicate a tornado large enough to rip my house to shreds, just big enough to spin a turbine.

The other benefit might be that the wind mill, what ever it would look like to harness a mini tornado, might be able to stay at ground level if the wide opening of the funnel is higher up, making maintenance on the windmill easier.  I wouldn't be looking to make the wind hang a U-turn, just redirect it a bit to come lower.

Maybe someone will know the answers to my questions and tell me I'm all wrong about this so I can forget about it. ;D

Offline cmxterra

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Re: Stupid questions about wind
« Reply #4 on: September 21, 2010, 06:11:20 PM »
I'm going to go with no. At least not with enough effect to be useful (like the magnifying glass)

The reason is that unlike light which does not get "backed up" when concentrated, wind has particles that will exert a force on the other wind particles when they get compressed like in a windsock.

So what you have is a windsock that gets "full" of air and the extra air just sort of spills over the edge thus not creating a jet of air coming out the back.

Get it?

Offline tamo42

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Re: Stupid questions about wind
« Reply #5 on: September 21, 2010, 10:43:32 PM »
There is a bit on this in mollisons permaculture notes.  You need the right landforms though.  Think of canyons in mountain passes and how the wind howls through them.  The same can be done on a smaller scale.

Offline phuttan

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Re: Stupid questions about wind
« Reply #6 on: September 21, 2010, 11:30:32 PM »

I think the only really useful method would be to place windmills where land formations naturally funnel the wind. Like positioning windmills in a deep saddle along a long high ridgeline or in a canyon that naturally concentrates the wind. Studying the area and determining the best location would work, but trying to build things up to the point of creating a man made effect would not be practical. You would have to build a mountain or valley. Just my two cents.

Pat

Offline AtADeadRun

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Re: Stupid questions about wind
« Reply #7 on: September 22, 2010, 03:21:49 AM »
In theory, yes, Mangy, the restriction will cause faster airflow.  Total energy, however, remains constant, so pressure drops, which would cause the turbine to behave oddly, I believe.  Moreover, to get any sort of significant effect, you'd have to have a *big* funnel, so it'd only be useful for a static, non-rotating (in the horizontal axis sense) turbine where one could be assured that the wind would almost always blow from the same direction.  If you've got that, you've already *got* the geographic funneling discussed by phuttan and tamo.  Trying to put a funnel big enough to have an effect on a horizontal axis turbine would just tear the turbine off the tower the first time the wind shifted faster than the servos could turn to match the new direction.

Offline Rorschach

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Re: Stupid questions about wind. Wind Concentration?
« Reply #8 on: September 22, 2010, 12:15:15 PM »
No mini tornado, but wind concentration is underway.

People are working on this and there are actually some in production:
http://gigaom.com/cleantech/kleiner-perkins-doubles-down-on-a-%e2%80%9cshrouded%e2%80%9d-wind-turbine-design/
http://green.autoblog.com/2008/12/31/new-wind-turbine-could-dramatically-increase-generation-efficien/
http://www.stormbladeturbine.com/
http://www.enflo-windtec.ch/english/turbine.html

Why do this? 
Betz Limit:
http://www.symscape.com/blog/virtual-wind-turbine-breaks-betz-law
http://www.windturbines.net/wiki/Betz%E2%80%99_Limit
http://en.wikipedia.org/wiki/Betz'_law
http://www.windturbine-analysis.netfirms.com/intro-betz.htm

Power is related to the velocity of the airflow cubed:
http://www.awea.org/faq/windpower.html
http://www.ftexploring.com/energy/wind-enrgy.html

Can we break Betz limit? 
http://www.ecofriendlymag.com/sustainable-transporation-and-alternative-fuel/can-we-overcome-the-betz-limit-in-windpower-extraction/ (pro)
http://www.ifb.uni-stuttgart.de/~doerner/diffuser.html (skeptical)

So in short people are proposing that Betz limit, the total theoretical efficiency, can be 'broken' by shrouding/funneling the wind  to the turbine.  That is the percentage of energy extracted from the wind can be increased above the theoretical 59.3 percent of a simple wind mill design.  Hope this was helpful.

Offline phuttan

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Re: Stupid questions about wind
« Reply #9 on: September 22, 2010, 08:47:20 PM »
Thanks for the links. Very interesting reading.

Pat

Offline Kwitzats

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Re: Stupid questions about wind
« Reply #10 on: September 24, 2010, 10:32:40 AM »
no shrouds are not funnells they manipulate the the air preasure (which may increase useable energy)and often are bigger on the leeward side. as far as breaking the Betz limit it imposoprobable(never say never), if you are extracting heat thats not exaclty wind power now is it?

Offline Rorschach

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Re: Stupid questions about wind
« Reply #11 on: September 24, 2010, 11:21:09 PM »
Funnel is an appropriate analogy at least for some designs.  I am not the only one to use this terminology: http://www.getsmartenergy.com/windcube/how-it-works.aspx. 

As far as using heat to break the Betz limit, I would say that is not kinetic energy that people would be thinking of trying to capture with a simple wind mill design.  I am skeptical myself that it can be broken as described by Betz, but was trying to present the discussion.

Offline mangyhyena

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Re: Stupid questions about wind
« Reply #12 on: September 27, 2010, 02:22:02 AM »
I freaking love these threads.  I always learn so much and get tons of links to read.  I'm heading in to read the links.  One day, my brain is going to explode, I'm sure.  Till then, this is fun.

Thanks, all. 

Offline Stein

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Re: Stupid questions about wind
« Reply #13 on: October 14, 2010, 11:18:55 AM »
The problem with wind turbines is constant wind, not too little wind.  By concentrating the wind, the swings from low to high would also be magnified which would be very hard on the turbine.

Offline Docwatmo

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Re: Stupid questions about wind
« Reply #14 on: October 14, 2010, 01:45:42 PM »
I've always had the same question about solar collectors.  Can you concentrate the sun with magnification (Just not to the point of generating enough heat to burn the material) and increase production?  I'm guessing no because I haven't seen any.  But just wondering. 

Obviously I don't know how the solar collector converts sunlight to electric charge (I'm gonna do a little research this afternoon), but Mangy's question sparked it.

Thanks

Offline tamo42

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Re: Stupid questions about wind
« Reply #15 on: October 14, 2010, 03:37:42 PM »
Actually that does work, and the most efficient cells are constructed that way.  Conceptually, solar cells are fairly simple.  Photons of light hit the material, which then absorbs that energy in the form of excited electrons which move.  We siphon them off for power.  The more photons, the more electricity. 

However, there are always constraints.  The biggest one is that you probably shouldn't melt the solar cell :).  It's also rather difficult to make a dome of the correct dimension out of a material that will bend the light but not block more light than you are gaining. 

Offhand, I'd say probably best way is to use a parabolic dish type of structure.

Offline soupbone

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Re: Stupid questions about wind
« Reply #16 on: October 14, 2010, 08:15:56 PM »
I'm no aerodynamic specialist or physicist, but from what I can see, anything placed between the force and the device being acted upon is counterproductive. Its not that a large - huge - funnel or a parabolic mirror won't increase the output, but can it be done in a cost-effective manner.

How big would a funnel have to be to effectively channel a windstream? How do you build, mount and maintain it? For the solar array, how big does the parabolic mirror have to be? How critical are the dimensions? Could sufficient additional power be produced to offset the cost of the funnel or mirror, the mountings and the bracing. (This is the heart of the matter).

I think it would be better to get a bigger windmill or add an additional solar panel than to go with add-on mechanical devices.

Again, this is just my opinion as I'm no expert.

soup

Offline AtADeadRun

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Re: Stupid questions about wind
« Reply #17 on: October 14, 2010, 09:07:01 PM »
Concentrated photovoltaics, using both mirrors and lenses, are on the market now.  A couple years ago I saw a plan for an installation intended for flat rooftop installation, which used a ten-foot-by-ten-foot articulated mirror array to focus about ten suns on a photovoltaic panel positioned above the array.  For the footprint and generated power, it was pretty cheap, though I don't remember the numbers now.

If we're going to talk CPV, or concentrated solar thermal energy, it might be a good idea to fork that discussion over to the solar power board and leave this for funneled wind.

Offline soupbone

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Re: Stupid questions about wind
« Reply #18 on: October 15, 2010, 07:52:23 PM »
AtADeadRun,

One last word from me on CPVs, please?

I asked my SIL, who works in the industry, about CPVs. He told me that this technology has been around for a while; the problem with it is that the lenses, mirrors, mountings, etc. are much more expensive than just building a larger solar array. Apparantly, there is no such thing as a free lunch.

soup

Offline AtADeadRun

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Re: Stupid questions about wind
« Reply #19 on: October 15, 2010, 09:07:13 PM »
No free lunch indeed, but the most expensive part of a solar array is the silicon semiconductor; if you reduce the amount of semiconductor by increasing the amount of incident sunlight, you decrease the cost per watt, though not quite linearly, since there's the cost of the mirrors/lenses and tracking rigs.  The Soliant stuff works that way, using relatively small areas of low-cost photovoltaic silicon to exploit several suns of concentrated solar flux.

Offline solarguy

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Re: Stupid questions about wind
« Reply #20 on: December 15, 2010, 11:30:30 AM »
There are some other issues with concentrating PV's.

1.  The magic semiconductor material itself, is more efficient when it's cold.

Adding concentrator lenses/mirrors will only make it hotter.  In general, the net result is more electricity, but not as much as you would predict because of the inefficiencies caused by the heat itself. 

2.  The lifespan of the material is directly related to it's operating temperature.  So yes, you can run extra photons through your panel with mirrors and lenses and get extra electrons out, but your panel will die sooner. 

3.  Those systems, to be effective, have to be aimed, ie, track the sun, adding more expense and complexity and things to go wrong.


Some people have tried getting around the first two problems by water cooling the pv panel, which also gets you solar hot water out of the deal, but the whole thing becomes expensive and unwieldy.

HTH,

troy

Offline mangyhyena

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Re: Stupid questions about wind
« Reply #21 on: August 08, 2011, 02:38:15 PM »
I was looking at the vertical axis windmills again, specifically the ones that use two halves of a barrel for catch blades.  I noticed that even though the barrel's open catch (inside part of half barrel) is facing away from the wind as it comes around, it's still fighting the wind; the wind is blowing against it until it gets far enough around that the inside is again exposed to the wind.

Is there a way to keep the wind off that half of the "wheel" until it turns to catch the wind again?  I was thinking about enclosing the half that doesn't drive rotation to keep the wind from pushing against rotation.  Better still, could a wall be built that redirects the wind that would push against rotation onto the side that drives rotation?

It's my understanding from other posts here that wind can not be redirected to blow the opposite direction.  In other words, if you hold a U-shaped pipe up so the openings face the wind, put your face in front of one opening while leaving the other opening in the wind, no wind would blow in your face.  (your head blocks wind from blowing into opening in front of your face). Is this true?  It doesn't seem right to me that wind would blow into one end and not come out the other end, if no wind is allowed to blow into the "out" opening.

If that's not true, then couldn't wind be redirected to push a vertical windmill on both sides of it?  Pushing from the front on one side while on the other side, being redirected to push from the back?  I realize that wind power is at least reduced after being redirected, but wouldn't even part of the wind power that would otherwise push against rotation, once redirected to aid rotation, help the vertical windmill turn better?

I'm sure this either wouldn't work or that even if it did, it wouldn't be practical.  I'm just curious about the theory behind it.  Is what I'm talking about even possible?

Offline archer

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Re: Stupid questions about wind
« Reply #22 on: August 08, 2011, 02:47:10 PM »
how about some type of fence that directs the wind from the returning side to the pushing side?

Offline LdMorgan

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Re: Stupid questions about wind
« Reply #23 on: August 08, 2011, 08:12:12 PM »
I was looking at the vertical axis windmills again, specifically the ones that use two halves of a barrel for catch blades.  I noticed that even though the barrel's open catch (inside part of half barrel) is facing away from the wind as it comes around, it's still fighting the wind; the wind is blowing against it until it gets far enough around that the inside is again exposed to the wind.

Is there a way to keep the wind off that half of the "wheel" until it turns to catch the wind again?  I was thinking about enclosing the half that doesn't drive rotation to keep the wind from pushing against rotation.  Better still, could a wall be built that redirects the wind that would push against rotation onto the side that drives rotation?

mangyhyena, you ask some of the best questions!

The answer to this question is "Yes!". What you are thinking of is called a Persian Windmill, and the design dates back at least as far as 500 AD. Here's a link:

http://telosnet.com/wind/early.html

While this arrangement is often called "inefficient", it really isn't. It does a very good job of converting wind energy into shaft HP. Especially on a technology-cost basis.

I've seen articles on a modern version about 6' high by 20' in diameter that could power a house in a very modest breeze.

Some of the more modern versions replace the sails with airfoils, which makes it work even better. And you can "feather" the air foils as they run through the no-power half of their circuit, which drops the operating drag down to VLI: Very Low Indeed.

As far as enhancing the wind goes, a funnel, diverter, collector, can be used, and does not have to be in "huge" to be effective.

You are also correct in being interested in vortex formation as a means of extracting additional energy. Googleup "Victor Schauberger" and you will be on yer way.

There is nothing simple about a vortex. See http://www.youtube.com/watch?v=XJk8ijAUCiI for a good demonstration.



Offline mangyhyena

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Re: Stupid questions about wind
« Reply #24 on: August 08, 2011, 08:47:40 PM »
LdMorgan, that was an excellent link.  I don't feel quite so crazy, now, at least for this idea.  Thank you for that.  Much appreciated.

If the wall, or wind blocker or redirector, were put on a swivel with a large vane, it should orient itself  in the wind, I'd think, preserving the best thing about a vertical windmill, which is operation in wind from any direction.

Anyway, all this has been a lot of fun.  I'm nowhere near knowledgable enough to work with the vortex.  But at some point, I'd like to take a run at a vertical windmill with walls to redirect wind.

Offline LdMorgan

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Re: Stupid questions about wind
« Reply #25 on: August 08, 2011, 08:49:21 PM »
I freaking love these threads.  I always learn so much and get tons of links to read.  I'm heading in to read the links.  One day, my brain is going to explode, I'm sure.  Till then, this is fun.

Thanks, all.

Concerning airflow through a u-shaped pipe: Shade one end from the wind (making a lee outlet) and air will flow through the pipe. Shading one end is the equivalent of  having a straight pipe pointing downwind. The wind would flow straight through the length of it.

My head-exploding contribution for today: Say goodbye to the Betz Limit and hello to the the Wind Sail Receptor. 

http://www.youtube.com/results?search_query=wind+sail+receptor&aq=3s&oq=windsail

This will make the present Multi-MW wind turbines as obsolete as chipped flint.

Offline mangyhyena

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Re: Stupid questions about wind
« Reply #26 on: August 09, 2011, 08:42:08 PM »
You know, that Wind Sail Receptor looks like it would work great for home applications as well.  Hard to believe it makes power in 5mph wind.  Adding and removing coils based on wind speed is absolute genius.  That thing makes all the other windmills out there, including the theoretical vertical mill discussed above, obsolete.  What a great example of what happens when a creative person looks for a better way, despite most experts' claims that no better way could possibly exist.  Replace Bentz Limit with Pintz Ona Limit.

Offline LdMorgan

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Re: Stupid questions about wind
« Reply #27 on: August 10, 2011, 01:18:55 AM »
Heh. Yes, indeed!

Offline ThePlainsman

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Re: Stupid questions about wind
« Reply #28 on: November 19, 2011, 08:55:15 PM »
Is there a way to keep the wind off that half of the "wheel" until it turns to catch the wind again?  I was thinking about enclosing the half that doesn't drive rotation to keep the wind from pushing against rotation.  Better still, could a wall be built that redirects the wind that would push against rotation onto the side that drives rotation?

I have thought about fixing a quarter round shield with a tail to rotate the shield into the wind to block half of the vertical turbine. You might have to angle the tail to increase the torque to keep the shield in place, but it should work.

Offline LdMorgan

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Re: Stupid questions about wind
« Reply #29 on: November 20, 2011, 12:25:00 PM »
I have thought about fixing a quarter round shield with a tail to rotate the shield into the wind to block half of the vertical turbine. You might have to angle the tail to increase the torque to keep the shield in place, but it should work.

Yep. Make the tail boom fairly long and the tail would not have to be large. The curved wall would be easy to pivot.

Should work like a charm. And with a vertical axis turbine, the tail vane would not have to work against gyroscopic forces.