New study on wind energy

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On 7/22/2011 1:52 AM, harry wrote:

You don't say...what a revelation.
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You _are_ aware that wind turbines, at least those honkin big ones, are slow speed?
Harry K
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On 7/21/2011 8:00 AM, Home Guy wrote: ...

...
The interaction between blades and the competing design factors (weight, strength, speed control, etc., etc., etc., ...)
A ceiling fan is built to keep the occupants of a room comfortable by moving air gently. A primary design consideration is to minimize noise while the fan rotates at low speed and to keep the construction costs, and therefore the purchase price, low. Energy efficiency is not a primary concern, because operation is inexpensive so most ceiling fans incorporate blades that are comparatively inefficient drag devices; rotating the pitched blades pushes air vertically out of the way. Wide, flat blades are inexpensive to build and work well as drag devices. More blades are better, up to a point, and the usual layout of four or five blades is the result of balancing trade-offs between efficiency and expense.
OTOH, a wind turbine must capture the energy in fast-moving air and rotate at relatively high speed. Slow rotation would increase the torque and require heavier and more expensive drivetrain components. For high-efficiency energy conversion lift-type turbine blades, similar to airplane wings, of twisted and tapered airfoil shapes are used. The blade design creates a pressure difference in windhigh pressure on one side and low pressure on the otherthat causes the blades to turn.
The reason for taper is the same as that for the shape of airplane wings and/or props--Bernoulli lift/pull. The longer path over a wing surface causes the velocity to rise and that lowers pressure on the upper (behind in the case of the prop/blade) which "pulls" the rotor in that direction for rotation.
A combination of structural and economic considerations drives the use of three slender blades on most wind turbinesusing one or two blades means more complex structural dynamics, and more blades means greater expense for the blades and the blade attachments to the turbine.
As noted before (and referenced in the Wikipedia article I bookmarked earlier), the increase in effectiveness of two over only a single blade fan is surprisingly little and the relative gain after that is smaller yet.
Also, again as noted, designs were within 75-80% of the theoretical limit when I last had actual performance data some dozen years or so ago; I'd expect continued refinements have pushed that to the upper value or perhaps even higher for current and next-generation blades (altho that's pretty closely held proprietary data, obviously, and not readily passed out over the 'net). What I'm aware of is what vendor provided to our electric co-op generation unit when evaluating the build/purchase decision to meet the mandated "green" generation reqm'ts coming. In the end, we chose to simply buy what we have to and keep conventional low-cost generation in our pool to minimize our customer costs as much as possible.
Following are some links that may be of interest; they don't delve into the real intricacies of blade design; that's pretty complex but do have some real-world design information and discussion of what actual design efficiencies are, etc., etc., etc, ...
<http://www.asr.org.tr/pdf/vol10no1p147.pdf <http://www.nrel.gov/docs/fy00osti/27143.pdf <http://practicalaction.org/docs/tech..._from_wind.pdf <http://www.bringaboutgreen.com/build...peed-ratio-tsr <http://www.raeng.org.uk/education/di...nd_Turbine.pdf
More than the above requires reading far more technical literature than I'm prepared to try to reproduce for usenet; if you're really, really interested, there are engineering texts but you'll need quite a lot of background.
Probably one of if not the standard...
<(Amazon.com product link shortened)>
Enjoy... :)
--
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Aaaawww...now you are trying to insert facts into an opinion discussion :)
Hary K
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On 7/20/2011 8:03 AM, Home Guy wrote: ...

Size has a lot to do with the design limitations.
Interestingly enough, the efficiency of adding blades is relatively small; a one-blade rotor is nearly as efficient as two and the third is even less of an increase.
While it doesn't go into a lot of technical detail, the wiki article outlines some of the basics of the various competing factors that go into modern generator blade design.
Limiting is more the physical characteristics required for survival and control and related cost and the efficiency obtainable within those restrictions as opposed to only the efficiency (altho modern designs run probably nearly 80% of theoretical Betz limit of kinetic energy extraction which is roughly 60% of input field KE.
I've not read the article for a while to see what, if anything has been added/updated, but had the link bookmarked--
<http://en.wikipedia.org/wiki/Wind_turbine_design>
--
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The trick is balancing the one blade model. Interestingly the same things apply to boat propellers. It also occurred to me there is another example of powered thin blades, helicopters.
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Fan blades and boat propellers act more like a a screw or auger. Airplane propellers and wind turbines are airfoils acting like airplane wings. Airfoils are much more efficent.
Jimmie
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Basic aerodynamics/physics. A fan blade is a wing. The larger the blade, the more drag (energy loss). Fans are designed to move a large volume of air and aren't particularly concerned about how much electrical power is used to do it.
Wind tubines have the opposite requirement. The blades are designed to be as efficient as possible as the larger the blade, the more wind is required.
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Robert Neville wrote:

The function of a wing is to provide lift in a vector perpendicular to it's surface.
Please explain how or why a wind-turbine blade needs to provide lift?
It actually can't provide lift, because (a) it's not turning under it's own power, and (b) if it did produce any lift, that lift would be a vector force pointing out of the down-wind-facing surface of the blade, and would act to pull the blades forward and destabilize the support colum and topple it.

So by that logic, a sailing ship would be propelled faster (capture more wind energy) by having a small sail vs a large sail.
Great logic.
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It does exactly the opposite. It converts "lift" into rotational energy. If the two processes aren't complementary, the world ends.

But a sail *does* have lift. Note that drag is a function of V^3.

Seem you're short a loaf, too.
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" snipped-for-privacy@att.bizzzzzzzzzzzz" wrote:

Is that your way of saying "yes, a smaller sail would propel a given ship faster than a large sail" ?
If that's not what you're trying to say, then please explain.
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I figured you for an idiot.

You wouldn't understand.
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" snipped-for-privacy@att.bizzzzzzzzzzzz" wrote:

I accept your evasion in answering my question as your surrender of this argument over to me.
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Only an illiterate moron could come to that conclusion.
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harry again used improper usenet message composition style by full-quoting:

The point I was making (which seems to have gone right over your head like a breeze of air) is that the amount of energy you can capture from the wind is proportional to the amount of surface area your "conversion surface" has. Since a wind turbines "conversion surface" must rotate in a stationary location, that surface must be angled with respect to the direction of the wind. But a ship naturally does not want to be stationary and hence it extracts the maximal amount of energy from the wind by having the sails at exactly 90 degrees to wind direction.
I'm surprised I have to explain such a fundamental and elementary concept in such excruciating detail. Are you perhaps female - and hence you have a problem grasping forces and physical principles?
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wrote:

As is the debt we are passing down to them. Aren't we wonderful!
--
Mr.E

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snipped-for-privacy@verizon.net wrote:

But what happens when the observations don't line up with the experimental/simulation/predicted data? A new report, just out today, shows:
Money quotes: * Earth's atmosphere is allowing far more heat to be released into space than alarmist computer models have predicted
* The study indicates far less future global warming will occur than United Nations computer models have predicted
* supports prior studies indicating increases in atmospheric carbon dioxide trap far less heat than alarmists have claimed.
* real-world data from NASA's Terra satellite contradict multiple assumptions fed into alarmist computer models
* there is much more energy lost to space during and after warming than the climate models show
* the atmosphere begins shedding heat into space long before United Nations computer models predicted
* The new findings are extremely important and should dramatically alter the global warming debate
* atmospheric humidity and cirrus clouds are not increasing in the manner predicted by alarmist computer models
* carbon dioxide emissions have directly and indirectly trapped far less heat than alarmist computer models have predicted
Article in Forbes: http://news.yahoo.com/nasa-data-blow-gaping-hold-global-warming-alarmism-192334971.html
Research Paper (PDF, 11 pages) http://www.mdpi.com/2072-4292/3/8/1603/pdf
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...
That's the great thing about science. It adapts to the new data.
Notice that it doesn't start out with a conclusion that it defends at any cost. More data comes in, new conclusions emerge.
Personally, I think it would be great if we found that CO2 levels don't cause any problems. As soon as that's the scientifically accepted conclusion, I'll accept it too.
Meanwhile, I'm not about to take my science from political leaders including Al Gore and Dick Cheney.
--
Dan Espen

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<snip>
So even the denialist report admits that GW _is_ happening. Clue. Science changes it's predications as date shows it is necessary.
Harry K
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Harry K ( snipped-for-privacy@hotmail.com) writes:

GW already happened, didn't you know... it's what eliminated the last 'Ice Age' (12,000 years ago), and it was fast, relative to how long it took for glaciation. The period which follows ice ages are called 'Inter Glacial Periods', the period we are in now. A time line of temperature (with low resolution) since the last ice age (after the fast, large rise), is a flat horizontal line. With resolution... it's up and down with a flat horizontal trend.
You need a better glue on your labels... they keep falling off.

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