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Ducted & Shrouded Wind Turbines (DAWTs)

May 7, 2010
Paul Gipe

Elena Diffuser-Augmented Wind Turbine (DAWT)


Update August 2, 2011: Elena Diffuser Augmented Wind Turbine (DAWT) Zero, Null, Nada Generation in One Year--After one full year of operation, the Elena DAWT has produced zero net electricity. . .

While in Paris I was reminded of an old Bob Dylan song with the refrain, "When will they ever learn, when will they ever learn?"

I ask myself this question a lot as I travel the world talking about renewable energy, because it seems "they never do learn" about what works and what doesn't work when it comes to wind energy. There's always another inventor with a super-duper new wind turbine and a gullible public to believe them.

I was in Paris after a speaking engagement on small wind turbines in Perpignan. So, I was invited to give a presentation at the Maison de l'Air on small wind turbines as well.

The choice of venues was apt. The building sits atop one of Paris' famed monts and commands a spectacular view of the city. The Maison de l'Air is devoted to all things associated with the atmosphere, including the wind. There's the rub.

At the end of March, the latest entry into the "who has the most outlandish claims sweepstakes" installed two Diffuser-Augmented Wind Turbines (DAWT) atop the Maison de l'Air.

In some ways it's refreshing to know that it's not just gullible Americans or Canadians who fall for the hype of these promoters. It feels better somehow to know that the French can fall for them too. France, after all, is the land of the famed TGV, which can take a traveler from Perpignan on the Spanish border to Paris in five comfortable hours. France is also the land of Descartes, Carnot, Pasteur and many other famed scientists and engineers.

Alas, the French are human after all, and they succumb to the siren's lure of installing a little windmill on the roof of an urban building, thinking they will produce a lot of electricity without all the bother and displeasure of one those "giant" windmills you see from the TGV as you speed toward Paris.

Eléna Energie, a Grenoble company, installed two of its Eléna 15 ducted turbines on the Maison de l'Air in Paris' 20th arrondisement. Placards on the building proclaim that the turbines will produce 15,000 kWh each at an average annual wind speed of 6 m/s.

Now Eléna Energie is very careful not to claim that the turbines will produce this much electricity at this site. The Maison de l'Air is in the city and surrounded by taller buildings. Also, a 6 m/s site is a very windy site.

Nevertheless, the placards suggested that the turbines can in fact produce this--somewhere in France.

Let's consider the company's bigger model for a brief analysis. The Eléna 30 uses a rotor 1.2 meters in diameter with a shroud or duct around it of 1.6 meters in diameter. The duct is 2 meters long.

For the sake of argument and to give Eléna Energie the benefit of the doubt-and they need it--let's simply say it has a shroud 2 meters in diameter, just in case they can't measure the shroud diameter correctly or I can't read the French correctly.

Well, you have to hand it to them. Eléna Energie's production estimates are something to behold. They claim that the Eléna 30 will produce 30,000 kWh per year at a site with an average annual wind speed of 6 m/s. This is 6 to 10 times more than what can be reasonably expected from real wind turbines.

I provide a range, should they in fact have an advantage from the two contra-rotating rotors. So, to summarize, I've given them a bigger shroud diameter, and then doubled that to account for the effect of two rotors. The result is that the Eléna 30 captures 133% to 266% of the energy in the wind. For comparison, most small wind turbines can capture only 20-30% of the energy in the wind.

I had to dig through my records to find another wind turbine with such outlandish claims. Eléna Energie out-promises even the notorious Wind Cube, the previous winner in my list of wild claims made by inventors of "new" wind turbines.

In comparison to Wind Cube, claims by Wind Tamer are downright reasonable. Even Enflo's claims of performance approaching the Betz Limit are modest in comparison with the wild claims of Eléna Energie.

Developers of many new Vertical-Axis Wind Turbines are fond of excessive and unsubstantiated claims of energy generation for their products. But VAWT promoters are pikers in comparison to Eléna Energies. Maybe the altitude in Grenoble or too much time in the wind tunnel (soufflerie) has affected the Eléna designer's judgment.

PacWind, at their worst, only claimed 500 to 1,000 W/m2 of rotor loading at rated wind speed. Eléna comes in at a whopping 1,000 to an utterly amazing 2,000 W/m2 of rotor loading at a diameter considerably larger than the 1.6 meters cited in their product literature.

Real wind turbines, such as the Skystream 3.7, deliver about 200 W/m2 of rotor loading at rated power.

Now, believers in such "breakthrough" technologies always attack the messenger for pricking their speculative bubble about a "miracle" machine that will spin huge amounts of electricity out of thin air.

The promoters of these machines are also quick to say, "Well how do you know it can't produce that much electricity, because we haven't tested it yet?" This is exactly my point. ElThe Eiffel Tower was at one time vilified by the elite of French society as a éna Energie is installing these "wind turbines" in prominent locations across France and yet has not done any testing outside the wind tunnel. This is, at the least, irresponsible.

It is also irresponsible for the maire of the 20th arrondisement to give these promoters a public venue to showcase their questionable wares.

There is a political debate in France about the future of wind energy. Opponents of renewable energy are quick to seize on installations such as these at the Maison de l'Air. One can easily imagaine them saying "See we don't need those big ugly monsters, we can use these cute little things instead."

In fact, Denis Baupin, Maire-adjoint (Verts) said about Paris, at the dedication of the turbines: ". . . nous ne souhaitons pas détériorer son paysage" (we don't wish to spoil the [Paris] cityscape) with real wind turbines. This is a Green Party member of the city council. If anyone should know better it should be a Green Party member. If the Greens can be hoodwinked by Eléna Energie and the unfortunate human desire to get "something for nothing," what can we expect of the general public and politicians less supportive of renewable energy?

There are dedicated and knowledgeable people in France developing renewable energy against great resistance from the "know-nothings" of our era. Let's hope that Eléna Energie and their invention quickly go the way of all those questionable inventions of the past before they do real damage to the future of wind energy in France.

Bon Vent (good wind)!

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