2014 Wind Turbine Buyer's Guide: Page 5 of 6

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Wind Turbine Buyer’s Guide
Wind Turbine Buyer’s Guide
Bergey Excel 6
Bergey Excel 6
Bergey Excel 1
Bergey Excel 1
Bergey Excel 10
Bergey Excel 10
Endurance E-3120
Endurance E-3120
Eocycle
Eocycle
Evance R9000
Evance R9000
Gaia-Wind
Gaia-Wind
Kestrel e300i
Kestrel e300i
Kestrel e400nb
Kestrel e400nb
Kingspan KW6
Kingspan KW6
Kingspan KW3
Kingspan KW3
Northern Power Systems 100-24
Northern Power Systems 100-24
Sonkyo Windspot 3.5
Sonkyo Windspot 3.5
Ventera VT10
Ventera VT10
Wind Turbine Buyer’s Guide
Bergey Excel 6
Bergey Excel 1
Bergey Excel 10
Endurance E-3120
Eocycle
Evance R9000
Gaia-Wind
Kestrel e300i
Kestrel e400nb
Kingspan KW6
Kingspan KW3
Northern Power Systems 100-24
Sonkyo Windspot 3.5
Ventera VT10

Certification indicates which certification(s) the turbine has, or if certification is in process. See the “Why Certification is Important” sidebar for more information.

AWEA rated power is in kW at 11 meters per second (25 mph). Note that this is power at only one point on the power curve. Comparisons between machines at any one point on the curve are not apples to apples. More useful are energy  (kilowatt-hours) measurements at the average wind speed at tower top at your site.

AWEA rated AEO (annual energy output) in kWh at a 5 meters per second (11 mph) average wind speed. This is useful information for comparing, but is only at one average wind speed, while residential wind sites may range between average wind speeds of 7 to 13.

Estimated AEO is predicted for 8–14 mph average wind speeds. These can give you an idea of what energy production to expect at your site, assuming:

  • Accurate measurement or prediction of the average wind speed at tower top.
  • The numbers in the table are accurate—seek confirmation from unbiased sources before buying any machine (see “Source of AEO”).

This section of the table is perhaps the most useful because it can help you be realistic about what a wind turbine might produce at your site. Rated power (watts) or power at any specific point on the turbines’ power curves cannot give you this information.

Source of AEO is the source of the annual energy output data. The sources include data derived from the field-verified energy curves on the certified turbines—i.e., Certified Energy Curve; manufacturer-supplied data, such as from Windcad, Bergey’s proprietary, Excel-based spreadsheet calculator; and the use of an AEO calculator, depending on the turbine.

Rpm is the turbine’s rotational speed at rated power. This may indicate two important aspects of the wind turbine’s performance. A lower speed for a similarly sized rotor usually translates into less wear and tear on the turbine, and less noise.

Governing system is the type of overspeed control. Turbines should have a method to protect themselves in high winds. Because wind power increases with the cube of wind velocity, enormous forces bear on a turbine in high winds. The top end of an accurate power curve can show you how well a machine protects itself. At regulation wind speed, the power curve of a furling machine will show a significant drop as the turbine turns itself out of the wind and slows down. In high winds, a machine with active blade pitching will show a flat line on the power curve, with little or no power reduction. Turbines with auto shutdown are designed to come to a complete stop.

Governing wind speed (mph) is the speed at which the machine is fully governed. Conservative designers choose to govern at lower speeds, knowing that long-term reliability is more important than capturing rare high winds. 

Grid-tie only (GTO) or battery-based (BB) indicates whether the machines are designed for direct batteryless connection to the utility or are for battery charging. Battery-based systems can also be utility-intertied, but besides needing batteries, may need additional equipment. GTO machines will not operate without a live utility connection.

Cost is shown in U.S. dollars, but doesn’t include shipping. Prices include various controls and sometimes even towers or more. Inquire with manufacturers for details of what you’ll get for your dollars.

Warranty details should be carefully scrutinized to see what is covered, and what the fine print reveals.

Comments (5)

Robert Dee_2's picture

Ian,
Your leading statement for this article is right on.

I love these HP cover shots showing people strapped to an 80 foot tower while a crane, probably another twenty feet over their heads, drops several hundred pounds of metal on them. Why anyone thinks this is glamorous is completely beyond me. It's dangerous, expensive, takes a lot of real estate and is so much more involved than PV today that I think for all but the very few with unlimited time and expenses wind is a no. This picture, if anything, should tell people capable of looking past the glamour to pass wind by.

Yes, I know the arguments about how wind compliments PV but at what cost? At an extreme wind velocity of 11m/s the small Kestrel puts out 1Kw according to your comparison sheet. Today that's three PV modules at a fraction of the cost with little or no maintenance and 30 plus years of output with a 25 year warranty not the 5 year one Kestrel offers.

And why are manufacturers publishing 11 m/s output, who has that kind of wind? It's unrealistic and a sad commentary on an industry that can't compete in the alternate energy business outside of large scale commercial turbines.
How is anyone realistically justifying wind? At $5,544.00 for the kestrel, without the tower and yearly maintenance, it's simply not feasible today.

Sorry, if anything this issue only confirms my belief that wind has very little place in small scale energy production.

Ian Woofenden's picture

Hi Robert,

Small wind is not for the faint of heart. I talk most of my clients out of it, especially as PV cost is decreasing. You have to either have a _great_ wind resource, an off-grid system with a dark and windy season, or a strong desire to just do it for it to make sense. It is a total blast (if you like that sort of thing) to install and keep a system running, but it's not cheap, easy, or reliable.

One of the presenters at the upcoming Small Wind Conference is doing a presentation titled "Go Big or Go Home", and I think there's a lot of sense to that. The economics and the quality of the equipment both improve as you get into small commercial machines. With the little machines, the cost of the tower to actually get it up into a good resource becomes a pretty big hurdle.

"Wind complements PV" is primarily a reasonable approach off-grid. On-grid, it's generally wiser to look at your resources and sink your money into generating with the most reliable and abundant, be that sun, wind, or falling water. With net metering, there's little need to have your generating source producing evenly all year. You can actually make all of your energy in your sunny season, and lean on your credit with the utility in other seasons.

As far as the 11 m/s, I agree that it's too high for a rating, but it's important to be clear that this is an instantaneous wind speed, NOT an average. And really, _any_ instantaneous rating is pretty useless -- for comparison with PV, comparison with other machines, and for energy predictions. What's really needed is an energy rating at various average wind speeds, as shown in the article table. Then you can (with luck...) find the average wind speed at tower-top height on your site and get a prediction of the kilowatt-hours a given machine may provide.

You are wise to point out that the turbine cost is just one piece of the _system_ cost. Typically, it's a modest fraction, with tower and balance of systems (BOS) each costing more than the turbine in most cases. Potential wind energy users need good pricing on installed cost of all components together before deciding to go for it. And some will go for it regardless of the economics, just as we decide to buy a new Prius, or a Caribbean cruise, a few years in college, or a week on the Riviera. In all cases, it's wise to know the costs and the benefits.

Ian Woofenden, Home Power senior editor

Robert Dee_2's picture

Ian,
Well put, you know wind better than most of us.
I also know the 'lure' of wind, the darn thing looks so easy just spinning around up there! And there certainly is a joy factor. I'm not saying I won't invest in it, I probably will but I already have over 10kw of PV in and a stream for microhydro. The thing that scares me is that we have this monster called the API (American Petroleum Institute) doing everything they can to knock down alternate energy, which actually beats the pants off of every other energy source out there in the long run, and I want things on the table to keep the disappointment factor as low as possible. We need to be the most honest guys out there or we'll get hammered.
I just heard the other day that Germany made 74% of its power from alternate energy (Thank you Hermann Scheer... RIP) and India is pushing solar now. Great! Technology will win over and we have that on our side.
Keep up the good work!
Robert

David Bainbridge's picture

I installed a Kestrel turbine last year and you immediately notice the much higher quality design and attention to detail. I had an African Wind Power turbine that was also produced in Africa which pales in comparison to the Kestrel. The support is also top-notch. I've emailed and gotten response to my questions in a timely manner.

Ian Woofenden's picture

Glad to hear it, David! I've been well impressed with the Kestrels I've put my hands and wrenches on, but have never lived with one, though I'd like to.

Kestrel has the distinct advantage over African Wind Power that they have significant financial backing. The AWP was a good original design, but the company was a bit thin, as was the U.S. importer.

Small wind is a hard business to be in, and I applaud Kestrel for making what seem to be good products, and taking care of their customers.

Ian Woofenden, Home Power senior editor

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