Ebay wind turbine guide

[DanB]

I get really frustrated with the whole topic of windpower on ebay - so I wrote this 'guide' (they let folks write guides now so I figured why not...).  There's lots of misleading stuff on ebay for sale and maybe I'm becoming too grouchy.  The page I wrote about windpower for ebay is here: http://reviews.ebay.com/Power-in-the-Wind-stuff-to-consider-about-wind-power_W0QQugidZ10000000001452



006?ssPageName=BUYGD:CAT:-1:SEARCH:3

If anybody notices anything wrong or thinks of any other good stuff to add there I'd be glad to change/edit it.

[harrie]

Great story Dan, you always seem to beable to explain thing where even I can understand. ha. Im glad someone is finely telling it like it is.

Great fun, Harrie

[commanda]

A = swept area in meters.

should be

A = swept area in square meters.

Power in the wind = 1/2 * 1.23 * 1.8241 * 4.4704^3 = 100.22 Watts.

And remember, if you double wind speed you have 8 times the power, so in a 20mph wind there would be over 400 Watts available!

should be

Power in the wind = 1/2 * 1.23 * 1.8241 * 4.4704^3 = 100.22 Watts.

And remember, if you double wind speed you have 8 times the power, so in a 20mph wind there would be over 800 Watts available!

Great article though.

Thank you for using metrics (mostly).

Amanda

[DanB]

thank you Amanda - and I apologize for mixing units.  Metric is cumbersome for me but sometimes it seems so convenient ;-)

[RayW]

Very realistic info.

      RayW

[lohearth]

  It,s good to see the info go out to where the buyers/sellers are. If it even stops one person from making a dreadful mistake, the effort is more than worth it

   Lohearth

[willib]

My comments are more gramatical and typo's than amanda pointed out.

but you asked ...so

third paragraph down at the end " educate yourself before you spend you money.  "

should be your.

under "Swept area and rated output"

"I often see 'light duty' small wind turbine rated for 1000 watts or more in high winds and then I'll see another manufacturer with a nice big heavy slow big machine thats rated for about the same output but in much lower wind."

too much use of the word big..

[DingBat]

In "Wind Power Facts":

it seems unlikely that those claims will every be contested.

"every" should be "ever".

--DingBat

[powerbuoy]

Nice write up. Probably the best eye opener is the turbine dia vs. wind speed vs. power table.

[kevindtimm]

I like it a lot, it should steer people in the 'right' direction

One note, 'compliment' should be 'complement'.

[asheets]

I enjoyed reading it.  One formatting detail, though -- does everything have to be centered, or can just the titles be centered?  I rather like left justification....

[froggie]

Hi

The only one thing I'd suggest, again a tiny thing, is to make the picture of your turbine that's up and on-wind clickable to see a larger and higher res image

Other than that, excellent, thanks for the table.

froggie

[fungus]

Maybe you should put a link to your site in there.

[vawtman]

Its almost 100yrs since this finding it still comes up.What did he use for a turbine and gen to get these figures.Lets think outside the box.Good ole mr b.

[DanB]

Hmm..

I think we should try to find out what's in the box - and why it's there, before we get too excited about thinking outside it ;-)

[Countryboy]

Dan,

  I think it would be helpful for folks if you talked about the relationship of turbine weight to swept area.  I know Mick Sagrillo is real big on heavy turbines.  The heavy beasts tend to be slow and durable, while a lot of the lightweight turbines are high RPMs and break down more often.  This isn't something you hear much about, but I think it's worthwhile to note.

http://egov.oregon.gov/ENERGY/RENEW/Wind/docs/Sagrillo.pdf#search=%22sagrillo%2Bheavy%2Bweights%22

Starting on page 13 of this PDF, they talk about weight per swept area.  

Cost per Pound

In my bias towards heavy metal, the "beasties" look really good on a dollars per pound basis when compared to the high-speed, lightweight turbines. But perhaps this measure says more about the weight of the machine and less about the cost. Robert Preus of Abundant Renewable Energy points out, "Just throwing weight at a machine doesn't necessarily make it more robust. However, there does seem to be a close correlation."

Weight per Swept Area

This provides an indication of machine robustness, which usually translates into longevity. Notice the range in this relationship, from less than 1 pound per square foot (5 kg per m2) to more than 4 pounds per square foot (20 kg per m2). I consider any machine with more than a 2:1 ratio as a heavyweight. I'd categorize machines between 1:1 and 2:1 as medium weight, and anything under a 1:1 ratio as a lightweight. Substitute "heavy duty" for "heavyweight," and you will understand my bias.

Weight per Tip Speed Ratio (TSR)

For a really dramatic comparison, compare weight and rotor speed in the machines listed here. As weight increases, rotor speed and, therefore, TSR decreases. In other words, there is an inverse relationship between TSR and weight. The lightweight, high-speed machines have low numbers, while the lowspeed, heavyweights end up with high numbers. The beasties with high numbers really stand out, don't they?

[richhagen]

Let me know if you have a turbine that beats Betz's limit.  I've never seen one.  The theory will hold until someone can prove it is wrong, and if the theory is correct, it will never be disproven.  Rich

[whatsnext]

+1. Left justification rules!

John......

[whatsnext]

Weight is the enemy of wind turbines for any number of reasons. Let's list a few:

1. All kinetic energy absorbed by the rotor prior to cutin is wasted.
   
2. Your tower has to be much more expensive to make it safe.
   
3. Your gen will be much more expensive.
   
4. Any out of balance conditions will be amplified.
   
5. Erecting your mill will be more difficult and when it falls it will likely cause more damage.
   
6. Your mill will be far less reactive to gusts.
   
   

Mass does nothing to produce electricity so there is no point in having it in the air unless it is absolutely required to function. A weightless wind turbine would be best if you could figure out a way to do it. If your logic made the slightest sense then making almost everything heavier would improve it and it does not.

John..........

[DanB]

Im not sure I totally agree.  Rotating weight has it's pros and cons - any energy before cutin that was used to get things turning is not really lost.  Heavy rototing parts help the machine to yaw more slowly -they help it to keep turning in between light winds etc...  I agree with much of what you're saying, but there are pros and cons to this stuff.

"#  Your tower has to be much more expensive to make it safe. "

Not really - the greatest load on the tower is thrust against the blades - that only has to do with swept area, not the weight of the machine.

" Your gen will be much more expensive."

Yes - but thats why so many companies are building high TSR light weight machines - more 'bang for the buck' but the drawback is they tend to break down sooner, they make more noise etc.

" Any out of balance conditions will be amplified."

I disagree there too.  If a big heavy slow machine with big heavy blades is 4 oz out of balance it's going to be a lot less amplified than it would be on a light duty/fast machine that was the same amount out of balance.  The biggest factor that amplifies balance problems is rpm  - not the weight of the machine.  So I would say the opposite - fast, lightweight, light duty machines will amplify any out of balance conditions.

"#  Erecting your mill will be more difficult and when it falls it will likely cause more damage. "

Yes - true.  The cost of this probably isn't terrily significant though compared to the cost of the whole system.

" Your mill will be far less reactive to gusts."

Maybe... not sure on that one.  More heavy stuff rotating will probably average things out a bit more but yes, I expect a 'weightless' machine will be more responsive in some conditions.  I don't think it's going to be significant though.  The heavier machine is likely to get 'tossed around' less and maybe stay pointed towards the prevaling wind on gusty days.

[ADMIN]

ASheets -- ahem. Harrumph. Centering all the text has been a 'tradition' of otherpower.com for some years now. I agree that it's a difficult to read, I don't like it much, and I've been producing all the new stuff that I write as left justified. harrupmh. Maybe this will serve as a gentle nudge to the boss to go light on those 'center' tags. <grin> Someone even threatened to list otherpower on 'websites that suck' because of the centered text a couple years ago. Now that we are laying out our up-and-coming book, we are seeing that such typographical minutiae can make a big difference in readability. Cheers, ADMIN

[whatsnext]

'Im not sure I totally agree.  Rotating weight has it's pros and cons - any energy before cutin that was used to get things turning is not really lost.  Heavy rototing parts help the machine to yaw more slowly -they help it to keep turning in between light winds etc...  I agree with much of what you're saying, but there are pros and cons to this stuff.'

Dan, None of this makes sense if you think about it. All energy needed to reach cutin is wasted by definiton because the mill puts out no power prior to it. A weightless rotor would gain speed instanty so there would be no need to store energy. Yawing more slowly is only of value if your mill is heavy. If it were lighter there would be no problem with a quick yawing machine and it would follow the wind better.

"#  Your tower has to be much more expensive to make it safe. "

'Not really - the greatest load on the tower is thrust against the blades - that only has to do with swept area, not the weight of the machine.'

Yes, really. The greatest load is not the only load and a moveable weight hung off the top of the tower places loads on the tower than many ignore. Having a weightless mill would reduce the loads on the tower so perhaps I should have said 'less expensive' instead of 'much less'. People on this site often ignore the relitively large loads vibration can cause. Just because you can't see it pushing the tower in one direction does not mean it's not there.

" Your gen will be much more expensive."

'Yes - but thats why so many companies are building high TSR light weight machines - more 'bang for the buck' but the drawback is they tend to break down sooner, they make more noise etc.'

Companies build cheap things because they are less expensive not because they are better. If they break down sooner it would be just as logical to assume that they are poorly designed. A light weight mill may actually be more expensive so equating hevier weight with quality is illogical. Cheaply built mills are cheaply built, what difference does the weight make?

" Any out of balance conditions will be amplified."

'I disagree there too.  If a big heavy slow machine with big heavy blades is 4 oz out of balance it's going to be a lot less amplified than it would be on a light duty/fast machine that was the same amount out of balance.  The biggest factor that amplifies balance problems is rpm  - not the weight of the machine.  So I would say the opposite - fast, lightweight, light duty machines will amplify any out of balance conditions.'

This statement assumes your out of balance condition would be the same and it would not be and even if it were the forces generated by the condition would not be helped with addition of mass. You would just have a heavier out of balance object. A weightless mill would have no weight balance issues at all no matter how it was built. There is also no logical reason for a light weight mill to not be slow turning if you so choose.

"#  Erecting your mill will be more difficult and when it falls it will likely cause more damage. "

'Yes - true.  The cost of this probably isn't terrily significant though compared to the cost of the whole system.'

The cost will be very significant once enough mills get built that these sort of problems happen more often. Dropping a heavy mill on someone's head is going to hurt.

" Your mill will be far less reactive to gusts."

'Maybe... not sure on that one.  More heavy stuff rotating will probably average things out a bit more but yes, I expect a 'weightless' machine will be more responsive in some conditions.  I don't think it's going to be significant though.  The heavier machine is likely to get 'tossed around' less and maybe stay pointed towards the prevaling wind on gusty days.'

No question at all about this one. A weightless mill would react instanly if it were possible to build one so it would be more reactive in ALL situations. There is no need to "average things out" when it would be just as easy to take advantage of the wind power that is there.

Clearly, building a weighless mill is impossible. It is still a far better goal than the idea that thowing iron into the air somehow make sense. I know that this site is all about practical DIY designs. I was just pointing out the impracticality of adding mass.

John.......

[vawtman]

Lets prove it wrong Rich its time.Do you now of any online stories of the dude Thanks and would love to read them.I know probably few attempts were made for big turbines but the little guys could make a run at it.I wonder how Eds L2 factors?

[vawtman]

I think airfoil vawts would benefit greatly from the blade weight. With hawts i think it would balance out but a heavier blade would be better for torque.Not sure just opinions.

[asheets]

Really?  I hadn't noticed that in the other articles....  I'll have to look again...

If it helps the ego any, I'm an admin of a church web site that the preferred GNU editing tool is "stuck" in center justification.  AND, it doesn't like importing from notepad or vi all that much, either.

[richhagen]

I see a few turbines posted on E-bay that claim to beat the Betz limit.  I don't believe them however.  I am not aware of any utility scale, or other serious machine that makes such a claim.  It makes sense to me that there should be a limit to the percent of the kinetic energy that can be recovered for a given set of circumstances.  As the wind is slowed in the turbine, it cannot move away from the machine on the downwind side as fast.  Its internal and pressure and volume (PV) energy would be effected more the more you slowed it down and it began to pile up downwind. At some point the total energy, kinetic and enthalpy, on the downwind side plus the energy extracted would equal that of the incoming wind.  An energy balance would show tht there would be no more energy available to extract.  I would barely know where to begin to calculate that limit, but that is apparently what this fellow did.  I suspect that his limit is an approximation, as it would seem likely to me that the real values would be functions of the windspeed and temperature as well.  One of these days I will have to read up on how he calculated it.   Rich

[richhagen]

From what I observe, my small mills sit there, and a gust comes along and they speed up to the point of cut in, generate for a bit, and then slow down to nothing.  If it is really a steady wind, they will just keep on spinning all the time.  I think that as the inertia is reduced, the losses during spin up and slow down would be minimized and one would actually see slightly more power, however, the gains would not be all that great though.  The energy lost to friction in the bearing would also be slightly affected, I would think, but again, even measuring that difference would probably be difficult.  In turbulance, the lighter machine would get pushed around a bit faster as well.  The main drawback for me would be that it would be very difficult to make a very light machine as strong as a heavier machine, and to do so would almost certainly add cost.  To me the more important effort should be towards increasing the reliability of the designs, not the efficiency.  I can make a slightly larger rotor that will more than compensate for the inefficiencies, and would gladly do so if I could make a machine that was even slightly more reliable, not that the machines built by others here are unreliable now.  I think the main thrust of his guide is to help prevent people from being taken advantage of by the sellers out there who are either little more than con artists, or are just plain ignorant of the products which they sell.  In that regard, I think this guide will be very helpful, if prospective purchasers of wind equipment actually bother to read it.  Rich

[scoraigwind]

Very nice guide.

turbulent and turbulence not turbulant.

"  In 1919 Albert Betz theorized that at best we can only slow the wind by about 1/3 and he calculated that the most power you can take from the wind is 59.26% of the total energy."

This is not quite right.  You can actually stop the wind dead at the rotor, but all the wind will then go around and you get nothing.  Betz's analysis looked at what happens when you slow the wind down by a certain amount and then how much power you get.  Let's say the wind in the wake is X time the wind upstream.  He found that the maximum power was available when X = 1/3.  In other words the wind is slowed to 1/3 of its upstream speed (and not slowed by 1/3 as you have written).  As it passed through the rotor it is going at 2/3, but in the wake it is 1/3.

Other comments - no need to calculate things to four places of decimals.  This is not rocket science.  It is not realistic to use more than 2 or maybe 3 'significant figures'.  Not a big deal, but I would write

 Diameter =5' = 1.52 m  (or even 1.5 m would do for me)

Wind speed = 10mph = 4.47meters/second

I did not see where the argument about weight started, but I agree with Dan that heavy is generally good.  Once the tower is erected then the weight is not a significant load compared to wind thrust.  Heavy machines do not wobble about as much as light ones whatever anyone says.  Heavy rotors do need longer or stronger gusts to get them to start up out of stall, but they will coast on through lulls, so there is no big handicap as far as starting goes, and once started they are just as efficient as light ones.  Putting in more weight is the simplest way to make the machine more durable and more efficient.  It may cost more but it's money well invested.

[drober23]

This should be posted somewhere prominently on this site as well.

A lot of folks come here with questions that show they do not understand this 'basic' set of guidelines.  Perhaps it could be the start of a 'beginner's corner' or 'read this before getting started' section.

Good stuff!

DJ Roberts

[mikemotorbike]

Consider removing word 'stuff' (non-descriptive, inaccurate) from title, i.e.: "Power in the Wind"; subtitle, "Clarifying potential misconceptions about wind power"

or, "Avoid these common pitfalls when condering building or buying a windmill"

State in the first paragraph the purpose of the guide, which is to clarify some misinformation common.  You stated this in first thread post and again in the guide's sixth paragraph under heading, "Wind Power Facts"

Quote: "I cannot think of another 'industry' where I see more misleading information out there than with wind power.  Because accurate wind speed is difficult to measure and many customers are not well informed it becomes easy to make unrealistic claims about a machines performance and it seems unlikely that those claims will ever be contested."

Indicate your intended audience (for hobbyists with intermediate skill level, some knowledge of math, or for people considering buying)

Break into the topic gently, make it easy to get oriented to the topic. Give a short overview of what you are going to write.

And why not mention fieldlines.com as a resource and research base, and share credit with the forum subscribers?

Please run a spell check, and definitely left justify, as it is not a poem.

http://www.spellcheck.net/

I feel I am better able to avoid potential pitfalls armed with the knowledge gleaned from reading your thoughtful and sincere guide. Thanks for sharing your real world experience and insights.