efficiency of homebrew

[tembelejderha]

Hello you all. I am greatly interested in wind turbines lately, I don't have hands-on experience yet but am greatly motivated towards building (at least) one turbine. So after lots of reading and surfing and stuff for about a week, and doing lots of homework, I decided that the best way to step-in is to order Hugh Piggott's book and follow the plans to construct a small machine.

As I am waiting for the book, I decided to ask my very first questions hoping that I'll not sound silly

1. How efficient are your blades? I guess that most of you use the Piggott design, or very similar ones. If not, how and what are yours? I don't ask for exact numbers, maybe just a comparison with those that are used for commercial systems (for example, Bergey blades).
   
2. How big is the effect of airfoil selection? What happens if I use a NACA XXXX rather than NREL XXXX or go for the Piggott's? I mean would things change drastically, or would there be an insignificant effect?
   
3. And alternators? Again I see that most of you use dual rotor Piggott-type alternators and How do they perform compared to professionally manufactured ones? (For example, like these: http://www.alxion.com/bin/e_eoliennes.php )
   
   

I know that what really matters is not efficiency but cost per watts, if not seeing YOUR OWN turbine running, which is priceless. But I just want to know how is HOME TECH vs. PRO TECH, if there is an answer.

By the way, thanks for the great knowledge you put here, for sharing. I sincerely appreciate it and am thankful.

Tembelejderha

[s4w2099]

Well. I have seen the famous AirX and they are not very impressive. Today I finished making my third alternator and let me tell you... HOMEBREWED ARE NICE. I am getting 10Vdc spinning by hand at 120 RPM N50 2x1x0.5, 12 pole, 42 turns per coil 9 coil 3 phase design, dual rotor 11 inch diameter, star.

Personally I am getting better results than using the AirX because of the cut-in speed. The AirXs that I have seen have to be furling very fast and they do not output as much power as they claim.

[Flux]

Measuring wind turbine performance is far from easy so you will not find many people who can reliably answer your questions.

My measurements have been on poor sites with too much turbulence to be of real value.

Any commercial manufacturer would choose a site without turbulence to do his tests.

Comparison with commercial units is also difficult because they always rate their machines for high winds ( often 28mph).

For direct comparison with machines produced here you need to look at commercial machines with no form of electronic power matching.

From what I have been able to deduce from measurements on a poor site, it seems that fairly simple blade profiles can produce about 60% of the Betz limit in low winds.

Loaded as normally done here the blades stall fairly early and I suspect that any attempt to follow precise aerofoils will give you no better results than the simple Piggott/DanB type blades, in fact many may do worse.

If you were to design to match the alternator properly in winds about 28mph then I am fairly sure the better profiles will do better( possibly significantly better)but you must choose the correct profile and match it properly. Many of the aerofoils designed for planes may show little improvement, they need to be chosen for suitable Reynolds number.

The axial air gap alternator is considerably more efficient at low power and I feel fairly sure that the axial machines as designed here will compare well with any commercial machine in low winds and in most cases perform significantly better. A commercial machine designed for reasonable efficiency at a rated 28 mph will be at a disadvantage in winds below 10 mph ( unless it has electronics to help it such as Bergey XL1)

Commercial machines designed and rated for 28 mph will probably produce twice the power of the type produced here in winds over 20 mph ( in fact many home built will be furling long before the commercial rated wind speed)

If you live in a low wind area then a well built machine of the type discussed here will probably stand comparison with most commercial machines of the same swept area and in some cases will knock spots off them.

If you live in a high wind area the total power produced by the commercial machine may be possibly twice the home built, but although the total power produced may be rather lower, the supply of energy on lower wind days may still make the home built a more reliable source of power. It depends on local wind conditions and the size of battery and possibly back up such as solar and how often that performs on low wind days.

If you want to change the design for higher wind production at the expense of low wind output then you would need to consider higher prop speeds and probably pay more attention to aerofoils, accept noise comparable with many commercial units and make changes to furling and other things.

Flux

[s4w2099]

Yep, That was what I was trying to say but it didnt came out so elaborated. Most comertial ones that I have seen have to be speeding extremely fast.

There is other advantage that the comertial ones have and its that theay are MUCH lighter. Comertial units rated at 500Watts often weight about 15 pounds. But like flux sais; most sites are turbulent and many under 12mph winds so you might be better off with a homebuilt.

[Gordy]

So far the thread has benn on mechanical efficency. You'll also want to concider $$$ to Watt efficency between two compairable units. A home built will be less $$$, how much less depends on your abilities to build, scrounge parts, ect.

Not only that, if you like building stuff and seeing it work. The fun of building and the saticfaction of seeing it work are priceless.

Gordy

[TomW]

Gordy;



A home built will be less $$$, how much less depends on your abilities to build, scrounge parts, ect.

Not to mention the home built unit will be less of a mystery to the user when it either fails or wears out, needs maintenance, etc.

Just an opinion.

Cheers.

TomW

[nothing to lose]

Although we seem to be mostly reffering to Daul Rotor types of home built, I think many motor conversions will out perform a comercail unit.

To many variables for anyone to say really for all cases. Like which comercail models, what wind speeds, etc.. as others mentioned.

How would we rate this type of thing?

For a motor conversion, a couple dollars of steel, $5 junk motor, $40 for magnets, a few dollars in wood for blades. Under $100 you have a unit that probably does as well or better than some $700 comercail units in nearly any winds in real life.

The motor conversion starts pumping some power while the comercail barely turns or not turning at all in the low wind range. Higher winds the comercail unit is making some power and the motor is making more. In max rated winds the motor is churning out alot of power and maybe the comercail unit is also.

Most places do not have steady high wind speeds, so overall in daily power output the motor would normally win in total power produced, compared to some or most comercail models of equal size and power ratings.

Of course I am thinking along the lines of a Jerry Garbogen type home built or a smaller Zubbly Baldor type compared to a $700 AirX or such comercail unit. I am certain the 3HP and 5HP Baldor motors in the yard will out perform a $700 unit also and at far less cost! I have about $5-$10 in each motor itself and it will cost far less than $700 to build them into full working wind gennies. I don't know what the cost of a comparable comercail model would cost, certainly far more than $700 I am sure.

I looked at a comercail unit recently and thought it was a real joke for about $700-$800! Not sure what brand that was but I built far better for under $150 total. I think their power rating was in 30mph winds and digging deep for details found in 10-20mph it was a joke! My unit had exceeded their max rating in lower more common winds.

I think in most places in real life the Garbogen would beat an AirX (or similar) in total monthly power produced if flown side by side. And that's what counts most, total power produced. As far as cost, built yourself and scrounging some parts about $100 maybe plus time.

Comparing bigger more powerfull and expensive comercail units then use larger motors, more magnets, bigger blades, and the motor conversions still come close enough to compeat well and at a major savings in $$ per watt still. Perhaps they even still beat a comparable comercail model, but getting into bigger more expensive models they may use various tricks like variable pitch blades, fancy controllers, and others which home built normally does not use.

[paradigmdesign]

Well, the guy I talked to from Bergey at the wind conference in Clevland I belive a few years back told me his blades were 55% efficient.  To me that seemed a little close to the Betz limit of  59.6%   for a no twist, no taper blade.  I guess if he was talking about % of the Betz curve, that number could have made sense, giving the blades an efficiency of about 33%.

Like DanB and others have stated many times, with the home brew machines, the blade efficency is more determined by how close you match the genny (resistance) to the blades, than by the airfoil used etc.

[Ungrounded Lightning Rod]

When the fuel is free efficiency is largely a side-issue, provided you have the space to build bigger.  Only getting 50% of Betz?  Increase your mill's diameter by 42% or more and you'll have as much power as if you were doing BETTER than 100% of Betz with the smaller rotor.

What matters is the charging current delivered to your batteries (times their voltage), how that varies with the wind, how your overall generation under your site's wind conditions compares to your usage, and how much it cost you (in money, time, and work) to build, set up, and maintain the system.

Commercial operations can claim higher efficiencies for their blade designs than something a homebrewer carves out of wood.  They may even be able to back up their claims, especially if they spent a lot of bux on aerodynamic design.  Compared to somebody who followed a formula and didn't spend months in a wind tunnel they may get a few percent more of that wind turned into mechanical power.  But when you compare the cost of their blades versus the cost of a somewhat larger homebrew set that collects the same or greater power, you'll see why their focus on efficiency is a salesman's red herring to confuse the novice.

[tembelejderha]

Thank you all for the answers.

As I said in the beginning, "I know that what really matters is not efficiency but cost per watts, if not seeing YOUR OWN turbine running, which is priceless." but I wanted to know sth about the eff. issue.

As far as I get it, homebrewed machines are pretty good especially in low wind speeds, which is the situation in my place. Also matching the alternator to the blades is sth very important that I should focus on.

Today I visited some shops and learned where to buy this and that.. I decided to start with a 10 footer. I will take photos as you folks do and submit the entire progress, hoping that it may be useful to some beginners like me. Now It's time for me to work!

Saludos!

[paradigmdesign]

I couldn't agree more. I am very much pro large prop. dia.  I belive the comercial turbine companies that use really high 27 MPH or greater rated speeds are being a little shady (unless they explain what the rated speed means to the comsumer in a factual way).  One thing you will notice about the comercial turbines, is when you get into the larger sizes 20KW-100KW their rated speed is usually at a respectable number (goes down).

[Gordy]

TomW,

As usual, GOOD point.

Thanks,

Gordy