Wind Turbine Ratings

[Chris Olson]

Hi, I guess I'm new here but this seemed an appropriate section of the forum to post what is one of my pet peeves in the wind power business.

That pet peeve is wind turbine output ratings.

It seems to me that the industry should require a 12 mph rating on wind turbine output instead of using the peak rating. While I realize other industries use peak ratings - as an example, the automotive industry where an internal combustion engine will be rated at it's peak dyno hp and torque - I think in the wind business it's misleading for customers.

Every time I talk to a potential customer about a wind power system it seems the people have misconceptions about what a wind turbine can do, based purely on that peak power rating. Take for example an AirX rated at 400 watts. It's really a 35 watt turbine, day in and day out on most wind sites unless you live in Kansas.

So it seems to me that the industry should require that all turbines have a more realistic output rating based on a 12 mph wind speed, which I consider the bare minimum average for a good wind site. And then with a peak or spike output rating tacked on to the real world 12 mph rating. Then a 1,000 watt turbine becomes a 180 watt turbine with a 1,000 watt peak rating.

I've thought about writing Denise Bode at the AWEA, Mick Sagrillo with Wisconsin's Focus on Energy, and various other people about this. But the chances of seeing it ever getting changed are slim to none.
--
Chris

[Rob Beckers]

Hi Chris,

The downside of posting in this section is that relatively few people can answer, since it's reserved for people in the RE business and we don't have too many members at this time that qualify for that.

As to rated wind speed; you are of course absolutely correct. The whole small wind industry is still very much a free-for-all with most companies engaging in deceptive marketing or outright lies. Worse, lots of government funding seems to be going to develop products that are known beforehand to be duds. All those yard-art VAWTs come to mind...

Russ Bailey send me a message pointing to the still new small turbine certification in the US (thanks Russ!): http://www.smallwindcertification.org/
The standard uses 11 m/s as the rated wind speed (or 24.6 mph). A good number IMO (and it's good to promote the use of metric rather than English units, much less confusion with the rest of the world). Lowering it to 12 mph as you suggest may be more in line with the winds that most turbines will encounter most of the time, but it does not convey what the turbine is capable of, something I see as the function of "rated power". Similarly, going any higher puts it in the realm of unlikely wind speeds that most turbines will almost never see (and of little consequence to energy production). You got to draw the line somewhere, and 11 m/s is a good place I think.

Similarly, the standard requires a calculation of energy production based on a real power curve, Raleigh distribution, and 5 m/s average annual wind speed. That is the number consumers should be interested in, as it goes directly to how much electricity their turbine could produce. It also provides a platform to compare turbines on an even footing.

You can find the standard itself here: http://smallwindcertification.org/pdfs/AWEA_2009%20Small_Turbine_Standard.pdf

This certification will become more and more important as more government funding will require it to get money. While this is a US standard, my understanding is that Canada is looking to either adopt it outright, or require essentially the same data.

-RoB-

[Chris Olson]

Hi Rob,

I guess I'm new here and didn't know which section would be best. So I'll try to move it to the general wind section as a new topic with a link to the post I made in the Pros section to sort of provide some continuity. Sorry about that :sad2:

Here's what I posted in the other section:
http://www.greenpowertalk.org/showthread.php?t=13685


Russ Bailey send me a message pointing to the still new small turbine certification in the US (thanks Russ!): http://www.smallwindcertification.org/


Yes, indeed. In fact, I talked to Brent Summerville, Technical Director for the SWCC, two days ago.

Currently, the pending applications for SWCC certification are only on grid-tied machines, except for one 48 volt battery charging machine in the list. Mike Bergey, for instance, does not feel seeking certification for the XL1 is worthwhile because he doesn't see lack of certification of the machine as a marketing barrier. BWC, however, is seeking certification of the grid-tied 5 kW and XL-S machines.

So even with SWCC certified turbines, there will still be discrepancies in ratings on wind turbines.

Brent Summerville said the only reason manufacturers will seek SWCC certification, for the most part, is so their machines qualify for government incentives to install renewable power systems. If those incentives fall by the wayside, then the only thing manufacturers can use the certificate for, really, is marketing. And it's quite expensive to get a turbine certified - $2,500 US just for the application fee, and costs approaching $20,000 to have the testing conducted by a certified facility.

So in the long run, even though Larry and Brent at SWCC have a good effort going, I don't think it will be the total answer. The only real answer probably lies in educating the general public so they don't buy a turbine rated at 1,000 watts and find out it only makes 180 day in and day out, and consequently think wind power doesn't work.

What I've found is that when somebody is looking at a wind power system, the first thing they ask is "how many watts is it?" If you tell them "1200 watts" that's what they expect out of it and they don't understand it if doesn't make 1200 watts first day on the tower. You can tell them that rating is only at 24.6 mph until you're blue in the face and it still doesn't register because they're convinced that the wind just HAS to be blowing at at least that and the thing isn't putting out 1200 watts.

Now, if you tell that same prospective customer "it puts out 250 watts @ 12 mph and can reach up to 1200 watts in really high winds" - that they understand. They see it putting out the 250 watts you said it would first day on the tower. And then you show them that at 250 watts this is what the machine is going to generate in kWh over a month's time, compare that to what they need to run their house over that same month's time, and they immediately see the relationship of what the turbine can do for them (or can't do for them).

But that's not the way most small wind power systems are sold. Too much emphasis is placed on that peak rating instead of what the machine is going to do day in and day out, which is usually in the fine print someplace in the brochure or advertising.

Brent Summerville agreed with me that using, say, a 6 m/sec rating is a good way to go. Brent's exact words on the phone, "I like that." But at the same time, manufacturers who would be forced into using a rating system that uses 6 m/sec won't do it because it makes it hard to sell wind turbines.
--
Chris

[Rob Beckers]

Hi Chris,

I've merged the two threads into one, so all the posts are now in the wind section.

The thing with the 6 m/s for rated wind speed is that it is really, really underwhelming. I mean, our own 6 kW Scirocco now becomes a 1.16 kW turbine (while with 11 m/s as the rated wind speed it would be a 5.7 kW turbine). Technically either value, 6 or 11 m/s, has equal merit, as long as all turbines use the same speed to compare against. For the consumer I think it would be much better to get away from 'rated output power' altogether. This is not what you're after when you install a wind turbine. Much better would be to publish a short table with wind speeds (4 through 6 m/s in increments of 0.5 m/s) with annual average energy production, based on a Weibull distribution. That will focus the customer on the need to find out what the average wind speed is going to be for their location. It will also allow for an apples-to-apples comparison between turbines.

Even if we were to get to that point (energy production instead of power), it will still be tough slugging with lots of room for confusion and disappointment. Probably 90+ percent of small wind turbines gets installed poorly, in the sense that they go onto short towers, in areas of disturbed flow etc. Production will be very disappointing in those cases. Then there's the problem that just about every small wind turbine out there breaks every 2 years or so. More disappointment. No amount of certification is going to solve those issues. Don't get me wrong though, simply getting to a standard rated wind speed is a huge improvement.

Of course manufacturers will only certify if/when they see reason to do so for marketing and sales purposes. They are running a business after all. Since (for now) only government funding will require certification, that will be their reason to pursue it. No surprise there. I have not studied the SWCC certification in enough detail so maybe I'm wrong; I know self-certification is not allowed, but it seems third-party certification is. That leaves the door wide open for the less-scrupulous (as in Chinese turbine manufacturers) to collude with third-parties that will 'certify' their less-than-stellar product (I know the SWCC is the final authority that signs off on certification, but all they have to go on is what that agency sends them). A giant loophole. Still, it's a step forwards.

-RoB-

[Russ Bailey]

Another important part of certification is the trial run under independent 3rd party control - the Mariah Windspire failed in a glorious fashion in the NREL trials.

Since that point they seem to have gone for so called 3rd party testing where they control the show and even got a decent report for basically the same machine.

20,000$ for certification would be cheap.

BTW - Mick Sagrillo and Paul Gipe are listed on the Small Wind Certification Org web site.

[Rob Beckers]

For most small wind manufacturers $20K is not that cheap. There are only a few, very few, manufacturers that sell enough small turbines to make a decent living, the majority either has some other form of income or is just scraping by. I'm not talking about the likes of Mariah that somehow found funding and could push their junk with the help of big (expensive) marketing campaigns. Unfortunately it looks like those that are serious about small wind turbines are usually very small businesses.

I know I can't justify handing over a Scirocco for testing by a third party: It's $30K in direct cost for turbine and tower, $10K or more to get it installed, and probably at least that much to have someone do data-logging for a year on it; making for a conservative estimate of $80K. There just isn't enough profit in selling small wind turbines to make up for that cost, not at current sales volumes.

-RoB-

[Ken Kacel]

I have always looked at performance based on Cut-In wind velocity and a power curve which shows the out put based on wind speed and then the cut-out velocity. A peak rating is decieving as in the Photovoltaic industry which would give output based on the summer solctice at solar noon with the panels perpendicular to the sun, hard to size your system when the peak performance happens once a year for 30 minutes.
The power curve is the cube of the wind velocity so twice the wind speed generates 8 times the power so to evaluate performance is only as good as the wind site analysis.

[Ben Colla]

I think a better way would be to beasure the area below the line in a power curve. OK, so you have to then have carefully defined definations, of the axis'.

Power may have to be measured every 100 watts, and RPM every hundred. You would end up with hundreds of little squares, below the line of the powr curve. Count all the 'complete' squares. That is your turbine rating. Squares that have the power curve cutting through them, don't count.

This would give a nice big number, and it's not open to interpretation. It doesn't matter what "wind speed" is claimed by the manufacturer. You get a real power output curve figure. Unless someone is lying about their curve, they are all equally accurate.

I guess you also have to have a maximum wind speed figure, otherwise some smart arse company will argue that their turbine will withstand 1,000 kph winds. So, maybe upto 28 m/s (100 kph), which most turbines will have to withstand. Maybe not make much power, but not explode.

[Rob Beckers]

I think a better way would be to beasure the area below the line in a power curve. OK, so you have to then have carefully defined definations, of the axis'.

Power may have to be measured every 100 watts, and RPM every hundred. You would end up with hundreds of little squares, below the line of the powr curve. Count all the 'complete' squares. That is your turbine rating. Squares that have the power curve cutting through them, don't count.

This would give a nice big number, and it's not open to interpretation. It doesn't matter what "wind speed" is claimed by the manufacturer. You get a real power output curve figure. Unless someone is lying about their curve, they are all equally accurate.

I guess you also have to have a maximum wind speed figure, otherwise some smart arse company will argue that their turbine will withstand 1,000 kph winds. So, maybe upto 28 m/s (100 kph), which most turbines will have to withstand. Maybe not make much power, but not explode.

Hi Ben,

I understand the desire to get to a single number to quantify a wind turbine. Your approach would have one big issue though: It's entirely possible to design/build a wind turbine that does very well in high wind speeds, and very poorly in those wind speeds that 99% of potential users see 90% of the time. In fact, if your metric was adopted it would encourage turbine makers to do exactly that. Designs that use blade pitch control to limit turbine RPM (which actually makes for a better turbine) would get punished, because their output is constant from a certain wind speed upward.

For that reason, if you want a single number, I would suggest taking a wind speed that's on the low side of 'economical' for small wind (since most turbines are installed so poorly that they'll only see low wind speeds anyway, or lots of turbulence, which has the same effect), say 4.5 m/s. Then use that as the annual average in a Weibull distribution, and calculate the production in kWh. That's your number: A 6kW Scirocco would be rated at 6,630 kWh that way, etc.

Keep in mind that the way energy production is calculated from a Weibull distribution uses the power curve, and multiplies power at a every wind speed by the duration (hours per year) that wind speed occurs. So, it is still very much along the lines that you propose, it just weighs the mid-level wind speeds much more heavily because that is what most people have most of the time.

There's a little more complexity to it than that: In reality wind turbines are usually not installed at sea level, so you have to agree at an altitude since air density affects energy production (I used 300 meters for the number above. The Weibull factor has to be agreed upon (over land K = 2 is the usual). Then there's turbulence; no turbine will do as well as theory predicts and the more turbulence the less energy, including for VAWTs (I derated production by 10% to account for turbulence, which means a tall enough tower that the turbine is in 'clean' air).

-RoB-

[Chris Olson]

Hi Ben,
For that reason, if you want a single number, I would suggest taking a wind speed that's on the low side of 'economical' for small wind (since most turbines are installed so poorly that they'll only see low wind speeds anyway, or lots of turbulence, which has the same effect), say 4.5 m/s. Then use that as the annual average in a Weibull distribution, and calculate the production in kWh. That's your number: A 6kW Scirocco would be rated at 6,630 kWh that way, etc.
-RoB-

The above sounds like probably the best method I've seen yet.
--
Chris

[Steven Fahey]

You have something of an "audience problem" here, I'm afraid, Chris.

Naturally people who gravitate to a wind power forum, like this one, will likely be in the know about variable wind speeds and questionable ratings on the turbines.

Somehow getting the message out to the average consumer and all people who sell the machines is the real battle. Paul Gipe, Mick Sagrillo, Ian Woofenden, Hugh, Dan B, and many others have been trying for years if not decades to accomplish this. Some of it's working, however they must tread carefully. Painting salesmen as scammers does the industry a disservice.

About the SWCC, be careful what you wish for. It will likely lead to more honest information being presented to consumers at purchase time. It will also lead to other "secondary" consequences. One that I forsee is the use of SWCC certification as a stamp of approval for federal grants, tax rebates, and municipal approval. Also not a bad thing, except for the DIY wind crowd.

You and I aren't likely to carry out certification tests on our stuff, are we? There may soon be coming regulations that make it more difficult for use to do what we enjoy. Less of a problem for those of use on a farm or way out in the country, but if you were to poll the population of Fieldlines members, for example, many are definitely "urban".

It's kinda like ethanol in gasoline. Great for fuel consumption for the general public, but it's tough for ultralight aircraft pilots who want to use regular gas in their planes but the ethanol boils off at 8,000 feet!

PS Yeah: Welcome to GPT!

[Jack Martin]

Wind turbines, like aircraft propeller blades, turn in the moving air and power an electric generator that supplies an electric current. Simply stated, a wind turbine is the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity.

[John Szegda]

Hello Chris Olson,

I am in the process of balancing my Exmork blades (Power Max). I remember reading your post on balancing and proper torque sequence for these blades. I can not remember what forum I read this information. Can you please post the procedure on this forum.

Thanks, John

[Chris Olson]

I am in the process of balancing my Exmork blades (Power Max). I remember reading your post on balancing and proper torque sequence for these blades. I can not remember what forum I read this information. Can you please post the procedure on this forum.


Hi John,

I assume you have the rotor with the two cast steel plates and three-bolt blades.

Torque all the inner bolts first, going around the rotor in a circle to 45 lb-ft. Then go around the outer circle of bolts to same 45 lbs. Then back to the inner circle and take them 72 lb-ft, then do the outer circle at 72 lb-ft.

Because the blades are sandwiched between the two plates, and everything is a tight fit (it fits so tight that there's not even any "play" to adjust tip distances), if the proper sequence isn't observed you'll end up with the blades not tracking properly. I've heard lots of people who have had Exmork turbines that have had a problem with a noisy blade and it's usually tip tracking causing the problem.

So after torquing everything down it's a good idea to check the tracking. If you have one that tracks off more than 5 mm loosen it up and retorque it in the sequence that will correct the tip tracking problem. If it still doesn't track right, then you have to shim it.
--
Chris

Edit to add some info: There's not near enough root area on those blades to properly align them on the hub and get consistent tip tracking results when assembling the rotor. I wish the roots were about 6" or so longer, 3" wider, and the hub itself about 12" larger diameter. This would provide much more accurate assembly and better alignment of the blades for tip tracking. But it is what it is, and once assembled, adjusted and torqued, I have never had one come loose or get out of adjustment even in high winds.

[John Szegda]

Hello Chris,

Thanks for the torque sequence. I would have thought the two outer bolts would be torqued first, but I guess they know what their doing. My hubs are not forged very well.
The inner single dimple was not drilled on center, so I ground it flat and will to use flat washers. That should help with blade shimming to correct tracking tolerances.

Thanks, John

[Chris Olson]

My hubs are not forged very well.

Yes, I know. I had one where the taper in the center of the hub was bored crooked so the hub wobbled when installed on the shaft. I should've scrapped it but I bored it, pressed and welded a 4140 CRM sleeve in it and re-cut the 1:10 taper in the bore. All for a $25 hub. I should've called CMS and had them ship out another hub but I think I was having a slow day when I did that.
--
Chris