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 Post subject: Re: Offshore wind farm may wreck NE winds for the Outer Bank
PostPosted: Thu Jan 10, 2013 10:30 pm 
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Sorry to beat this dead horse, but just have to clarify a couple of misstatements
1.
Quote:
I dont live in Hatteras or even NC and this decision is totally up to the residents of those islands.


Actually the state of NC has no say after 3 miles. The Outer Continental Shelf is governed by the Federal government, and offshore energy leases are specifically managed by the Bureau of Offshore Energy Management (BOEM) a division of the Department of the Interior
Quote:
Outer Continental Shelf (seaward of 3 nautical miles from shore): the Outer Continental Shelf Lands Act of 1953 (43 U.S.C.A. 1331 et seq.), passed in coordination with the Submerged Lands Act, confirmed federal jurisdiction over the resources beyond three nautical miles from shore and created a legal process for developing those resources (such as oil and gas)


2.
Quote:
SSK I'm not sure what you are trying to show with the contrails.
given the right conditions a pressure differential will result in condensation. Wind turbines obtain their drive by using a foil to produce a pressure differential to drive their rotation. In extreme humidity their bound to produce condensation. With falling pressure or temperature, the condensation would not have sufficient energy to overcome the latent heat of vaporization and would not be reabsorbed for quite some time (if at all) The photo does not indicate large scale turbulence or pressure disruption outside of the immediate wind farm area just a bunch of selective air particals made visible and then mixed around by rotating blades. Take a bunch of smoke machines and spin em around in circles in front of a few low speed fans and the visual effect would be somewhat similar


Actually everything I stated is correct and most of Johnny Rotten's description is incorrect. The photo is clearly displaying wake turbulence as I stated. However, it was scientist/engineers from Lawrence Livermore Laboratory who pointed this out. You may see the article on wake turbulence here with the caption under that photo of "Normally invisible, wind wakes take shape in the clouds behind the Horns Rev offshore wind farm west of Denmark."
http://www.sciencedaily.com/releases/2011/04/110426151040.htm

3.
Quote:
Guys, the hub height on most serious offshore turbines is 70-80m with an 80m diameter. That means the wake is 30m-40m in the air. (ie higher than your kite)

It is incorrect, to suggest that the disturbed area would be contained and limited to the height of the rotor. The disturbed area will spread out, and as other studies have shown that is all the way to the water surface.
You can see a good image of that here
http://www.nrel.gov/energysciences/csc/projects/wind_energy_simulations

4.
Quote:
Anyone that would complain about a Wind-Farm that's gonna be 6-miles away and up wind of his kite-spot, is a bit self-centered and really couldn't care about anyone else living on the planet other than himself


I agree, and I do not think anyone was complaining throughout this whole thread, and no one said it was a bad thing. This thread was only a discussion of the theoretical possibility of some kind of effect downwind of a large wind farm. At 6 miles could there be an effect? The answer is a definite maybe depending on size, type, number, etc. But this is not to say that for kiters the effect would be bad or even noticeable. We know that it can effect the climate and wind in the local area, and a lot is still to be learned. We know these effects can go kilometers to miles downwind.
Quote:
While the distance the wake effect extends is still a matter of debate, experts agree that downwind wake effect from an individual commercial wind turbine can persist for a minimum distance of eight to ten times the turbine’s rotor diameter (equaling up to more than half a mile)and can persist even longer where turbulence is low, such as in offshore locations. Some experts even estimate that wake effect continues even longer, possibly extending several kilometers.

We also known the it is not just wake effect but other climatic changes such as pressure, temperature, and density and this too can cover a large area
Quote:
Dr. Roy says, "It's something like the wake from the propeller of a boat. Now this added turbulences mixes air up and down and creates a warming and drying effect near the ground." He says the affects can be felt for miles.



However, it is unlikely that even if there was some bad localized effects for kiting that anyone who lives or kites on OBX would complain much. The most pressing issue on the OBX is probably the erosion of the island. This drives politics, economics, and environmental decisions. The rate that the islands are shrinking is pretty shocking and is a result of natural processes, but have been exasperated by man made activities/decisions. This is even further exasperated by an increase in the rate of sea level rise. Pea Island which is the gateway to the prime kiting locations on the OBX is likely to be gone in many places within our lifetime. If you believe in a tie between sea level rise and carbon emissions, then I surely doubt you would fight the development of any windfarm that could effect your kite spot on OBX. Because if there is no island left then you do not have a kite spot. For those who spend time in OBX I strongly recommend reading Dr Stanley Riggs "Battle for the North Carolina Coast"
http://www.amazon.com/The-Battle-North-Carolinas-Coast/dp/0807834866
or any of his articles on line. He is the leading expert on NC coastal dynamics. It is pretty eye opening to see aerial photos from the 1930s overlayed with the current photos, and see how much of the island has been lost. You may come see how we have made and are making some bad policy decisions.


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 Post subject: Re: Offshore wind farm may wreck NE winds for the Outer Bank
PostPosted: Thu Jan 10, 2013 11:12 pm 
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The number of wind farms in the works around the great lakes is pretty staggering. You can almost tell by looking at the layout that there are gonna be unexpected downsides we will have the joy of learning about in years to come. Once again it looks like the interests of business and politics raming a concept forward with little to no real concern for its true overal impact.

Until we wize up and follow the example the planet has set for us we are doomed to wreck it. The eventual answer is solar. Its an example that has been set by every blade of grass dating back to the primordial soup! Why we cant focus our collective ingenuity and resources in that direction I cant fathom.


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 Post subject: Re: Offshore wind farm may wreck NE winds for the Outer Bank
PostPosted: Thu Jan 10, 2013 11:46 pm 
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SSK wrote:
Image


All else being equal, if the impact was measurable (read: significant) they wouldn't build wind turbines directly behind each other, that would be bad design as in the case of that pic, so that picture has to be bogus. Having said that, the turbines here in Ontario are a few hundred meters from each other and scattered somewhat randomly (maby not), and given that they are a significant investment, their placement would have been optimized for wind force. So, now we're talking 6 miles down the line..?

A second point, 6 miles down the line, a 1 degree change in wind angle would account for significant difference where that 'disturbance' would be noticed onshore. So chances are the same local spot might not be affected on a regular basis, is all I'm saying.. good discussion tho and supporting data.


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 Post subject: Re: Offshore wind farm may wreck NE winds for the Outer Bank
PostPosted: Fri Jan 11, 2013 12:36 am 
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Quote:
All else being equal, if the impact was measurable (read: significant) they wouldn't build wind turbines directly behind each other, that would be bad design as in the case of that pic, so that picture has to be bogus.


Wrong. I really want to give this a rest, but people keep saying completely wrong things, on facts that anyone can read about. There is suprisingly a ton of research on this on the internet. If you are going to bother to dispute something, at least do yourself a favor and read up first. That photo is clearly legit and is used by the wind power industry in numerous studies to emphasize a known issue and problem. There are reasons that they have to be put the turbines in a line, but the industry clearly knows that the downstream turbines suffer from measureable and significant power loss. They are working on better designs and spacing to fix this. But the loss has been shown to be as much as 30-40%. If you desire you can read this all over the internet if you have a little technical knowledge. From the Energy Center of the Netherlands study (but you could find many more similar industry studies.)

Quote:
During the last decades more and more wind turbines have been installed in large wind farms. The grouping of turbines in such a farm introduces two major issues: a wind turbine operating in the wake of another turbine has a reduced power production (because of a lower incident wind speed) and shortens the lifetime of the rotors (because of an increased turbulence intensity). For example, Neustadter and Spera found a reduction of 10% in power output for three turbines separated by 7 rotor diameters; Elliott mentions in his review a ‘considerable reduction in efficiency’ and ‘[the windfarm] produced substantially less energy’. For full wake conditions power losses of downstreamturbines can be 30-40%, but when averaged over different wind directions, losses of 5-8% have been reported. In order to reduces power losses and to improve the lifetime of the blades it is necessary to obtain a good understanding of the behavior of wind turbine wakes in wind farms.


Not only is it measureable and significant but it costs millions of dollars in potential power loss and a lot of research and study is going in to mitigate it.


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 Post subject: Re: Offshore wind farm may wreck NE winds for the Outer Bank
PostPosted: Fri Jan 11, 2013 2:47 am 
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SSK wrote:

2.
Quote:
SSK I'm not sure what you are trying to show with the contrails.
given the right conditions a pressure differential will result in condensation. Wind turbines obtain their drive by using a foil to produce a pressure differential to drive their rotation. In extreme humidity their bound to produce condensation. With falling pressure or temperature, the condensation would not have sufficient energy to overcome the latent heat of vaporization and would not be reabsorbed for quite some time (if at all) The photo does not indicate large scale turbulence or pressure disruption outside of the immediate wind farm area just a bunch of selective air particals made visible and then mixed around by rotating blades. Take a bunch of smoke machines and spin em around in circles in front of a few low speed fans and the visual effect would be somewhat similar


Actually everything I stated is correct and most of Johnny Rotten's description is incorrect. The photo is clearly displaying wake turbulence as I stated. However, it was scientist/engineers from Lawrence Livermore Laboratory who pointed this out. You may see the article on wake turbulence here with the caption under that photo of "Normally invisible, wind wakes take shape in the clouds behind the Horns Rev offshore wind farm west of Denmark."
http://www.sciencedaily.com/releases/2011/04/110426151040.htm


Please Point out the incorrect statement:
a)Given the right conditions a pressure differential will result in condensation.
b)Wind turbines obtain their drive by using a foil to produce a pressure differential to drive their rotation.
c) In extreme humidity their bound to produce condensation.
d) With falling pressure or temperature, the condensation would not have sufficient energy to overcome the latent heat of vaporization and would not be reabsorbed for quite some time (if at all)
e) The photo does not indicate large scale turbulence or pressure disruption outside of the immediate wind farm area just a bunch of selective air particals made visible and then mixed around by rotating blades
f) Take a bunch of smoke machines and spin em around in circles in front of a few low speed fans and the visual effect would be somewhat similar

I'm not stating there's not disturbances within the wind warm area. But the picture you posted is COMPLETELY misleading withrespect to the ACTUAL shape and more importantly length of wake.....the link you posted of the CFD analysis speaks to this quite well. THAT is the wake.... The photo you posted is nothing more than placement of air particles that were at some point in contact with the tip of the turbine blades


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 Post subject: Re: Offshore wind farm may wreck NE winds for the Outer Bank
PostPosted: Fri Jan 11, 2013 3:23 am 
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Quote:
Please Point out the incorrect statement:

Basically there are some correct statements, but you overall premise and supposition does not make any sense. Yes of course there is condensation here as a result of a pressure differential, I explained that earlier. But somehow you are trying to say that there is simply a pressure change without boundary layer separation and the flow remains laminar makes absolutely no sense. The turbulent flow and pressure change are results of the same physical principles. Secondly you suggest that turbulent flow if any ends at the boundary of the farm, it just simply is not so. Please do not believe me and educate yourself and read some of the articles that I posted. I swear I am not making it up, only presenting what I have read in numerous studies. The point is that is does extend beyond the farm for a good distance possibly several kilometers or more. And that distance is a factor of many variables. If you disagree then do not tell me contact the guys at Lawrence Livermore. NOAA, or the National Renewable Energy Laboratory and tell them they do not know what they are talking about, and you have a different idea.


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 Post subject: Re: Offshore wind farm may wreck NE winds for the Outer Bank
PostPosted: Fri Jan 11, 2013 5:34 am 
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SSK wrote:
Quote:
Please Point out the incorrect statement:

Basically there are some correct statements, but you overall premise and supposition does not make any sense. Yes of course there is condensation here as a result of a pressure differential, I explained that earlier. But somehow you are trying to say that there is simply a pressure change without boundary layer separation and the flow remains laminar makes absolutely no sense.


Please provide the quote where I said the flow was laminar....

Engineers are well aware that a significant pressure disturbances are non-beneficial and potentially damaging to the turbines. So when designing the arrays the modelling initially indicated that most of the "wake effect" would be cleared up after 5-7 rotor diameters....maybe 10 for the big ones....well reality turned out to be a little further once they started building massive windfarms like horns rev on a scale that the models have not yet been proven. So in reality it was closer to 15 rotor diameters before the wake effects had piddled out and the flow could be considered laminar for the purposes of power generation.

SSK wrote:
The point is that is does extend beyond the farm for a good distance possibly several kilometers or more. And that distance is a factor of many variables.


We are talking distance of 6 MILES!!!! AT LEAST an order of magnitude higher than any distance where wake effects are even discussed in an area that is not even within the direct plane of the turbine ie 0-25m

Try to imagine the amount of energy that would have to be added to a particle of air to keep it rotating in a turbulent manner for 6 MILES when being acted upon by a strong outside force like a 20knot wind.

Although not in the same plane of reference, the distances and power values are similar....a 747 uses about 65 MW of power flies at about a 6 MILE cruising altitude.. Ever had your session ruined from the wake of a plane flying by at 30,000 ft?

SSK wrote:
If you disagree then do not tell me contact the guys at Lawrence Livermore. NOAA, or the National Renewable Energy Laboratory and tell them they do not know what they are talking about, and you have a different idea.


Instead of misinterpreting my posts as well as the writings of multiple authorities in the wind energy field, I suggest YOU contact them, and explain your concerns quoting the aritcles you have read. I found these researchers to be very willing and open to discuss their area of research and more importantly calm a somewhat paranoid kiteboarder about a windfarm that is popping up that they're not "stealing our wind"


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 Post subject: Re: Offshore wind farm may wreck NE winds for the Outer Bank
PostPosted: Fri Jan 11, 2013 1:47 pm 
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Polarstorm, the placement of turbines around the Great Lakes has more to do with maintaining setbacks from houses than optimum placement. They are squeezing them in wherever they can..


SSK, I find your posts thoughtful and concise. Nice work.


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 Post subject: Re: Offshore wind farm may wreck NE winds for the Outer Bank
PostPosted: Fri Jan 11, 2013 4:04 pm 
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This is an absolutely fascinating discussion.

SSK or anyone else who may have an opinion or facts to share, Now that I see even my home spot is slated for a large wind farm approximately 6km away from shore I am going to try to put a positive spin on this.
We often suffer from a condition called decoupling (we call it doming). When the water is cold and the wind is warm it has a tendency to separate from the water surface this works both ways warm water and and cold air seems to have the same effect. So it can be windy as hell slightly in land and the buoy about 6km out shows 20 kts but on the beach it is calm, its like the wind forms a dome over the beach. Do you think having a large wind farm 6kms out can have a positive effect by forcing the wind to mix and therefore not decouple?
Probably wishful thinking but wouldn't that be great?


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 Post subject: Re: Offshore wind farm may wreck NE winds for the Outer Bank
PostPosted: Fri Jan 11, 2013 4:52 pm 
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Quote:
Do you think having a large wind farm 6kms out can have a positive effect by forcing the wind to mix and therefore not decouple?

We experience the same on the East Coast in the Spring. Would be a great thesis topic to do some modeling and simulation. I would think it is a definite maybe. But again the magnitude of any benefit would be determined by size, scale, and distance. Decoupling occurs due to an inversion where the air near the ground is colder than that above it. Strong stratification sets in, so that the turbulence becomes effectively lifted and decoupled from the ground. So the properties of wind turbines on the environment would definitely be converse to those properties that cause decoupling. It is clearly known that the higher atmosphere air (in this case warmer) would be pulled down and mixed with the decoupled colder air. There are several studies out there that show the temperature effect in the immediate environment around wind farms. A study in Texas showed this actually extended the growing season of an orange farm (cooler in the day, warmer at night). Studies also show upwelling behind windfarms, and this case would bring warmer water to the surface. I would guess that theoretically it is possible.


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