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Rooftop and Urban Wind

October 16, 2009
Paul Gipe

Earthtronic's Honeywell Windtronics WT 6500--A Review


I've reviewed the series of preproduction wind turbine designs from Earthtronics twice before. See below.

Alas, as I was sitting in my doctor's office today I picked up a copy of Popular Mechanics and there was Windtronics. PM was gaga over Windtronics and unquestingly regurgitated Eartronics claims. So I felt I needed to look at the turbine again.

The product has evolved since I first came across it. It has grown from the Eathronics 760 to the Windtronics 6000 and now is identified as the Honeywell WT6500.

Lest the Honeywell name lend some kind of legitimacy to the WT 6500 note that the Honeywell trademark is simply used under license. Tellingly, "Honeywell International Inc. makes no representation or warranties with respect to this product."

While Earthtronics had provided estimates of annual generation for the previous models, there is now more information posted on their web site than before.

There are no units in use. One turbine has been "tested" in a wind tunnel. Thus, all claims about the product are projecture.

Those who have followed the debate about performance measurements of small turbines realize that testing in a wind tunnel is not testing at all. Wind tunnel "tests" are useful only for design not for estimating the performance of the wind turbine in the field.

Though no turbines have been tested in the field, Earthronics has hired a public relations company.

The WT 6500 is 6 feet in diameter. The 1.8 m diameter rotor sweeps 2.6 m² of the wind stream. Using the standard power rating, a turbine of this size should be rated at 500 W.

Earthtronics web site depicts mounting the wind turbine on the roof and this theme is repeated throughout the product literature. Mounting a wind turbine on a roof is never a good idea. For why, see Rooftop & Urban Wind.

Overspeed Control

It is not apparent from the web site that the Honeywell Windtronics turbine has any form of aerodynamic overspeed protection. Details on the web site are sketchy at best. The web site asserts that a "smart box" will stop the turbine in high winds. How it does so and what happens if it fails is not explained.

Bird Friendly

Earthronics claims that the turbine is more bird friendly than conventional wind turbines. This is unlikely. Of course, since no turbines have been installed the claim can't be proven or refuted. For general commentary on claims such as this see Fantasy Wind Turbines and look for the comments about birds.

Wind Power Classes

Earthronics now provides estimates of annual energy production based on Battelle PNL's wind power classes 3 and 4.

Wind Power Classes represent a range of wind power densities at various hub heights. Battelle provides three heights: 10 m (33 feet), 30 m (~100 feet), and 50 m (~160 feet).

Battelle's Class 3 represents wind power densities from 150 to 200 W/m² or approximately average annual wind speeds from 5.0 to 5.5 m/s at 10 m hub height. The 10 m hub height is approximately that of the rooftop mounting shown on Earthtronics web site.

Battelle's Class 4 represents wind power densities from 200 to 250 W/m² or ~average annual wind speeds of 5.5 to 6.0 m/s at 10 m.

At the height where any wind turbine of this size should be used, 30 m, the wind speed in Battelle Class 3 increases to 5.9-6.5 m/s and in Class 4 to 6.5 to 7 m/s.

Annual Energy Estimates

Let's give Earthronics the benefit of the doubt and pick the higher value. For rooftop heights of 10 m, the turbine will see 5.5 m/s in a Class 3 and at it see 6.0 m/s in a Class 4.

At a height of 30 m, the turbine will see 6.5 m/s in a Class 3 and 7.0 m/s in a Class 4.

Based on the performance of wind turbines of similar size, we can estimate how much the WT 6500 can generate under good conditions.

At 10 m (rooftop)

At rooftop heights the turbine may produce 850 kWh/yr in a Class 3 and 1,050 kWh/yr in a Class 4 wind resource. Earthronics claims that the turbine will produce 2,000 to 2,500 kWh/yr respectively. Earthronics claims exceed likely generation by 2.4 times.

Note that though these estimates are at rooftop heights, they are not estimates of generation on rooftops. All turbines on rooftops have performed substantially below estimates.

However, Earthtronics wisely does not say at exactly what height the wind turbine will generate the estimated amount of electricity.

At 30 m (tall tower)

At 30 m heights the turbine may produce 1,300 to 1,600 kWh/yr in a Class 3 and Class 4 resource respectively. Thus, if the turbine was installed on a tall tower, Earthtronics claims exceed likely generation by only 1.5 to 1.6 times.

 

As performance claims for small turbines go, these are not outlandish. They may never be achieved but they won't be achieved by a much smaller amount than many other "new, never seen before" inventions.

Power Curve

The power curve doesn't look realistic because it begins at zero and charges toward infinity. Nor is the uses of odd terms such as "plate power" mean anything to cognoscenti.

Nevertheless, we can pick one point off the power curve and its table to see if the estimate is realistic.

At 11.5 m/s, the power curve says that the WT 6500 will reach 1,000 W. Let's call this the rated power. The performance at rated power is about 41 percent. This is high, but not outlandishly so. The rotor loading at rated power of 1 kW is 381 W/m² which again is high, about that of the old Air 403, but not outlandishly so.

The turbine is definitely not a 2 kW turbine as suggested on the web site. At best it is a 1 kW turbine and more properly called a 500 W turbine.

 

General Commentary

1. ". . . generating energy from the blade tips rather than through a mechanical center gear. . .

Most wind turbines of this size don't use a gearbox, so I am not sure what they are referring to. They must be setting up straw men to simply knock them down.

There are commercial wind turbines too, Enercon being the most well known, that don't use a gearbox. The rotor drives the ring generator directly. Thus, the ring generator is certainly not original with Earthtronics.

2. " . . . by practically eliminating mechanical resistance . . ."

Mechanical resistance is not a significant factor in wind energy generation. And many wind turbines don't use a gearbox so they don't have the resistance that Earthtronics is referring to.

3. ". . . operating in a greater range of wind speeds . . ."

In my books I emphasize that this is usually a tip off to watch for. There's very little energy in the wind at low speeds. So if a wind turbine claims to capture wind energy at very low wind speeds, the response should be "so what. There's not enough energy there to make a difference."

4. ". . . highest output, lowest cost per kWh installed turbine ever made."

Ignoring the fact that they have not actually installed any of these turbines and thus hard to justify such a claim, we can examine the product's relative cost.

Earthtronics claims that the turbine can be installed for $7,500. It sweeps 2.6 m². Therefore, the relative cost is $2,900/m². This could be comparable to some overpriced small turbines but is nearly three times the typical cost of commercial wind turbines of ~$1,000/m².

And if we consider the rated wind speed of 11.5 m/s of 1,000 W, the $7,500/kW is again three times that of a commercial wind turbine of $2,500/kWh.

5. ". . . rarely start turning before . . ."

This is a classic straw claim. Who cares when it "starts turning". This means nothing except for the turbine's entertainment value. As Mick Sagrillo would say, if it's entertainment you want, buy a whirligig.

6. ". . . installed cost is approximately ½ of the cost of traditional turbines . . ."

Maybe in comparison to some overpriced small wind turbine but not to commercial turbines which cost one-third as much as Earthtronics' WT 6500 and we know that commercial turbines work and have the documentation to prove it.

7. ". . . Honeywell Wind Turbine is a 2 kW turbine that creates 2,752 kWh/yr in Class 4 winds."

As noted above, it is more realistic to call this a 500 W wind turbine and at best a 1 kW system. Further, the 2,752 kWh claim is more than that of 2,500 kWh found elsewhere on the web site.

Conclusion

My evaluation of this product hasn't changed since it was first brought to my attention. There is no substantiation to back up the promoter's claims and the claims themselves are exaggerated.

It is unlikely that this 500 W wind turbine will deliver the performance promised in either Michigan or Ontario.


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