AIR X POWER CURVE FAILURES AND NOISE PROBLEMS

Now to be fair, as we have said, the Air X alternator and bearings and shroud and everything about it appears much more durable than the cheap ametek motors I use.

To be fair, my neighbor who has one loves it, despite the poor test results, especially cost per amp, it has received from many private and government funded studies.

To be fair, they are a sexy unit. Very expensive in dollar per amp, but fairly popular as far as wind generators go; just not for me. They are far too noisy, make far too little power and are far too expensive. The noise of those blades is becoming infamous in the wind generator industry and harbors around the world. I just had a conversation with a neighbor of the 'new' one at the dock and he hates it.

Small blade gens spin faster and so the blades are more likely to hit stall speeds in lower winds and as a result, they are going to be noisy. So noisy in fact, one neighbor at the harbor threw a rope in his neighbor's Air X in mid-winter just to shut it up. I also notice that the Air X rocks back and forth in little gusts. I guess the folks at the factory sell that as a 'quick response' to wind direction variations. Maybe so. What I noticed while watching and listening to one (sometimes for an hour or more) is that when they do that little side to side shuffle they get noisy. I think if it were my design I would increase the size of the tail so it stayed pointing forward more often. I think maybe that tip noise is aggravated by the swaying motion. A test with a side by side wind vane and an Air X would give some answers there.

NREL has also done some AIR X NOISE AND POWER TESTS that didn't show the Air X in a very favorable light. Apparently some manufacturers either make their output graphs/charts confusing or simply stretch the truth a bit on their output...who knows. Our blades and smaller ametek gens are refurbished and cheap and in the teens, can outproduce an Air X 2 or 3 to 1. If you don't like the output, simply get a bigger gen; they're cheap in comparison.

Our blades don't have any of the Air X cost prohibitions, low output problems or even noise problemsp; not until winds are much higher. We try to carve them so they don't stall out until 40-50 knots or more. Below are two articles from Paul Gipe, who has done extensive tests on blades and gens in the hills of Tehachapi. I think the Air X has solved some of their power/control issues as Paul's article is a few years old, but just the same, in our side-by-side test our 6 footer was putting out 2 to 3 times the power in 14-18 knot winds for about 1/4 the price. Something to remember when shopping.

Here's Paul's Data, followed by our own side-by-side test:

AirX Fails Power Curve Tests
 January 29, 2003
Copyright 2003 by Paul Gipe. All rights reserved.

Tests during 2002 at the Wulf Test Field demonstrate that the AirX fails to meet the manufacturer's power curve by a wide margin.

Key words: AirX, Air 403, Southwest Windpower, Small wind turbine testing.

Disclosure: The three versions of the AirX tested as well as a Whisper H40 were provided by Southwest Windpower at no charge in lieu of noise measurement services provided by Paul Gipe.

Beginning in early 2002 I began measuring the noise emissions from a preproduction version of the AirX at the request of Southwest Windpower. As part of these measurements I also monitored the AirX's power curve. (My report on the noise emissions from the AirX will be posted separately.)

During these tests I noted that the AirX was not meeting its power curve. Previous measurements of the Air 303h and 403 indicated that these turbines also failed to meet their advertised power curves. However, the AirX failed by a much wider margin.

In cooperation with Southwest Windpower I've tested three versions. These I call AirX.1, AirX.2, and AirX.3 respectively for lack of a better description. For the most part the difference between the versions is programming on the chip that controls the AirX's operation.

None of the AirXs tested met or even approached the power curves in Southwest Windpower's owner's manual.

Power was measured with a watt transducer and average during 1-minute periods. Wind speed was recorded on the tower with the turbine. The turbine was tested at an elevation of 4700 feet (1430 meters) in the Tehachapi Pass. Data was corrected to sea level, 15 C conditions. For more details on the test technique, altitude and temperature correction, averaging period, and possible losses in the conductors see http://www.chelseagreen.com/Wind/articles/PowerCurves.htm .

While the performance of the three versions differed, sometimes markedly, from one another, the overall performance fell far below that of the Air 403 and that of the manufacturer's proffered power curves.

Southwest Windpower clearly, and fairly state on page 28 of the AirX Owner's manual that the manufacturer's power curve represents "instantaneous wind speed". This is a significant improvement over previous power curves for the Air 303 and 403 that were not so identified. Nevertheless, purchasers will expect that the turbine produces the advertised power on a consistent basis, which it does not.

The AirX will briefly reach rated power but begin to regulate. When it does so, the average power produced is well below rated. For example, if the AirX reaches rated power and begins to regulate, the turbine may be braked for as much as half a minute. When it does so the average power is half that of rated, or 200 W. Actual performance is even less that this.

The AirX compares well with the Air 403 and meets the more conservative of the company's two power curves up to 23 mph (10 m/s).

At rated wind speed the AirX delivers only 103 W 99 W, and 51 W respectively, not the 400-525 W advertised. In the worst case, the AirX.3, the turbine only produces 10% of the advertised instantaneous power claimed. This is probably a record of some sort.

As Michael Klemen points out, this isn't the whole story. Energy production is reduced by a lower than expected power curve, but the energy generation lost is not quite so dramatic.

In a 12 mph (_5 m/s) wind regime with a Raleigh distribution, the AirX.2 and AirX.3 will generate 80% of the 388 kWh/yr produced by an Air 403. In a 14 mph (_6 m/s) wind regime with a Raleigh distribution the AirX.2 and AirX.3 will generate 65% of the 612 kWh/yr produced by an Air 403.

The AirX is both subjectively and quantitatively quieter than the Air 303 and Air 403. However, this is accomplished at a significant sacrifice of performance.

AirX Noise Emission Measurements

January 30, 2003 Copyright 2003 by Paul Gipe. All rights reserved. Both versions of the AirX monitored at the Wulf Test were qualitatively and quantitatively quieter than the Air 403.

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Disclosure: All AirXs tested and a Whisper H40 were provided by Southwest Windpower in lieu of payment for noise measurements by Paul Gipe.

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Background

Southwest Windpower's Air 403 was notoriously noisy. While not the noisiest wind turbine ever made, its widespread distribution caused an unusual number of noise complaints.

In late 2001 Southwest Windpower asked me to measure the noise from a preproduction version of the AirX. Beginning in 2002 and through the first half of 2002, I conducted a series of noise measurements on two versions of the AirX. For lack of a better descriptor I called them AirX.1 and AirX.2. I also measured the power curve on a third version, the AirX.3 but I have not made any noise measurements on this unit.

I've withheld publishing the data collected until now for several reasons. First, I had other obligations. Second, I considered the versions I tested defective products and returned them to the manufacture for correction. They were defective because they failed to meet the manufacturer's power curve. While the noise measurements on these units were complete, the fact that the product would likely be modified by the manufacturer to correct the power curve defect suggested that the final production version would not be represented by my tests.

The final version I received, the AirX.3, operated similarly to the AirX.2 and the noise emissions are likely comparable. Further, Southwest Windpower has been shipping various versions of the AirX for more than one year. I have no idea how my versions compare with current production.

For a complete description of the rationale for testing, the methods employed, the terminology used, and my test equipment, see http://www.chelseagreen.com/Wind/articles/noiseswt.htm .

Critical to understanding the following data is the difference between sound pressure levels of ambient noise, and noise with the turbine operating. It is the difference between ambient and the turbine noise plus ambient that determines the noisiness of the wind turbine. The difference determines the noise from the turbine at a specified distance from the turbine. This calculation in sound pressure level is then used to arrive at the source emission strength in sound power level (LWA). The latter is the noise at the source, the wind turbine. This value can be used to project noise at varying distances from the turbine and can be used to compare one wind turbine with another.

Air 403

To recapitulate earlier results on the Air 403, in winds from 8-10 m/s (18-22 mph), the Air 403 would emit an annoying "buzz" most of the time. The Air 403 sound power level or emission source strength (LWA) was 88 dBA at 8 m/s and 91 dBA at 10 m/s.

AirX

The AirX is so significantly quieter than the Air 403 that it was difficult to measure a sufficient difference between ambient and turbine plus ambient in wind speeds greater than 18 mph (8 m/s) to calculate valid values for sound power levels above this speed. In the accompanying chart for the SPL Summary for the AirX.1, the ambient noise can be seen rising steeply with increasing wind speed (wind noise in nearby willows) while the noise from the AirX rises less rapidly.

As seen in the second chart, Calculated Emission Source Strength, both the AirX.1 and the AirX.2 emitted about the same amount of noise. The sound power level for the AirX.1 and AirX.2 at 8 m/s (18 mph) is 80 dBA or 8 dBA quieter than the Air 403.

The AirX accomplishes this by stalling the rotor or turning the turbine off so the blades don't begin to flutter. This is a very effective method for reducing the noise emitted by the AirX, but it does so at a cost. The AirX fails to meet its power curve by a wide margin.

A few books by Paul Gipe who seems to be a pretty busy guy.
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WIND vs BLADE SIZE vs EXPECTED WATTAGE
On February 22nd, the NOAA wind data below (circled) indicates 13-18 knots at a bouy about a mile from where I live at anchor.

My friend had just completed installing his Air-X Marine, 42 inch blade at the top of his mizzen and was checking out his fancy monitoring circuits, bleed-off circuits and I was walking down the dock and heard it whizzing away. I noticed it would slow down drastically quite often, then speed up in the gusts. Our blades have a more even RPM through lulls and gusts, so I wanted to see how many AMPS he was getting as the wind varied.

I shouted down below 'Hey, how many amps are you making? Got that circuit finished?' and he shouted back 'Come below and see for yourself.' He sounded very proud and he had done a lot of work on it, so off I went down into his very nice boat.

I saw the meter go down to 0-2 amps in the lulls and then when the gusts hit, it would go up to 3 to 4.5 amps. If a really strong gust hit, it would go up to just under 5 (about 4.8 or 4.9). I said, 'I'll be genereous and give you 5 in the strong gusts, but really 3 to 4.5 is about all you are getting and it sure does spend a lot of time at zero or 1 or 2 amps.' His hospitality soon faded with my comments (ooops) and I said I was going out to my boat and see what I was getting.

I don't run fancy gear; I have a fat rotary switch, an automatic wind switch and a manual override, a few meters on my helm and a nice battery A-B switch. I also have those cheapie 6 LED christmas light thingys that tell me from anywhere in the boat how my batteries are doing.

I took out my rather expensive multimeter (I am a union electrician who designs robotics) and changed the leads to measure amps, set the dial to measure amps and wedged one lead firm down into a fat wire where some copper goes into a battery clamp and the other lead onto the post where the gen comes down to the battery box.

I reached around and flipped the A-B battery switch to OFF so the only way power could come from the wind gen was through my meter.

BANG! 4.8 amps, 6 amps, 7 amps and then the gusts, 8, 9, 10, 9, 8, 10, 10.8! (oh boy this is really great!!!) and then POOOF! The fuse blew in the meter.

Most multimeters are only designed for 10 amps. I don't know how many amps I would have gotten in those really STRONG gusts where he was getting 4.5 amps, but I do know that when he was in the 3 amps to 4.5 amp range, I was in the 8 amp to 11 amp range.

That was the best comparison I had ever done and that is the power you can expect from our six foot blades with the larger, (more expensive) 7 inch gen. The standard gen we sell with our 4 and 6 foot blades will be a bit less. If you want the larger gen (you need good winds and a 5 or 6 foot blade to drive it), then you will get between twice and three times the power. Period.

Our 4 foot blade puts out about half the power of the 6 foot blade, or just slightly more than the Air-X Marine Gens. That makes sense. The Air-X is 42 inches and ours is 48 inches, so the Air-X has an airfoil that is at least as good as ours (close anyway). We aren't knocking these units. They are much better weather proofed than the cheap ametek gens I use, they look sexy with that 'seagull' body and come with a casing, fin, mast/pole etc. and if you want to pay more than four times as much for less than half the power and you think that's prudent, go for it. Their unit will probably outlast our unit since we use refurbished Ametek PM motors.

However, if your goal is POWER for the best PRICE, you won't find a better blade and gen on the planet than the kits we offer. No way. Not for this price performance. That little comparison taught me a lot about just how good our blades really are.

And you know what was really telling? His AirX was at the TOP of his mizzen mast, a good 20 feet higher than my blade was. Had I mounted my blade as high as his blade I probably would have blown the meter out in the LIGHT wind gusts! Here are the NOAA wind speeds for the day I did this test.

Note: we provide generator/motors to wind generator customers AT OUR COST. These are often ametek motors from third party vendors and we guarantee they will work or are replaced. Our vendors are professional surplus houses, electronic gear reps etc. Not all motors are rated for this or that voltage, but ALL are guaranteed to work within the parameters below and ALL will work with wind generator blades to provide 12-18 volts of charging power from wind power as described herein. Please remember we cannot and will not guarantee a specific ametek model number and as these motors get rare and hard to find, please consider yourself lucky that we sell them at cost for our blade customers. They aren't easy to come by and are considered 'The Gems' of the industry.

Our website offers classes and items for sale through RETAIL OUTLETS and ONLINE SUPER STORE. Most importantly, we offer support. Take a look at our FEEDBACK from customers and you'll see:Support is number one at KCK.