A recent report from Dr. K. D. Visser, Ph.D. from the Department of Mechanical and Aeronautical Engineering of Clarkson University finds and predicts increased efficiencies in small, ducted wind turbines when compared with same size, open rotors.
The ducted or shrouded design is technically known as Diffuser Augmented Wind Turbine or DAWT as indicated in the report. According to tests and measurements claimed in its description, the DAWT WindTamer (tm) design almost doubled the efficiency of the conventional open rotor Horizontal Axis Wind Turbine (HAWT) devices. The document indicates additional benefits found with the DAWT turbines tested in comparison with HAWT: quieter, safer and reduced tip speed ratio (TSR). TSR is the ratio of a blade tip speed over wind speed, an indicator of its efficiency. The lower TSR in this case results in less wear and fatigue according to the report.
Wind turbines with similar characteristics to the DAWT WindTamer (tm) have been in research and development since the 70’s and a primitive model, the Éolienne Bollée, was built and patented in 1868 in France. Northrop Grumman, in particular, found almost 40 years ago yields close to six times higher than conventional open designs with their Vortec Rotor Shelter. In 1994, Robin Johannink founded Vortec Energy Ltd. in Auckland, New Zealand to generate electricity from the Vortec Diffuser Augmented Wind Turbine. The Vortec DAWT weighted approximately 22-ton and the system was mounted on a circular rail. A 17 meters high, 7.3 meters rotor diameter and 1 MW peak power demonstration plant, Vortec-7, was built in Huntly on the west coast of New Zealand. The strong turbulence created in the outlet made unfeasible to have other wind power plants close together. The company developed plans for larger turbines with up to 66 meters rotor diameters and 5 MW. In 2001 the company dissolved due to economic unfeasibility.
Smaller models are working in Europe: Caphorn 10 in France and Enflo Wind Power in Germany later restructured as Windtec Systems AG in Switzerland.
More information about the DAWT WindTamer (tm) and the report “Wind Tamer Turbine Performance Report 1kW – 15 kW Performance Predictions, WindTamer Report 11
November 2009” can be found at http://www.windtamerturbines.com/ and at http://money.cnn.com/news/newsfeeds/articles/marketwire/0564960.htm; about DAWT in general at http://www.ifb.uni-stuttgart.de/~doerner/diffuser.html.
Comments
Notice that they don't define efficiency. I bet it is based on the diameter of the rotor and not on that of the shroud. But you still have to build that shroud.
The figures for the 7.3 meter diameter rotor are implausible, or else the figures for the 66 meter diameter rotor are awful. Or both. (My back of the envelope calculations suggest the first choice.) Or perhaps the 7.3 diameter turbine is used in a river or something. But they don't say that. You have to wonder about the accuracy of the other information.
Lincoln, thank you for your comments. Actually, Vortec-7 was built in New Zealand as a prototype using technology licensed from Northrop-Grumman and with a very large amount of money invested by private companies and the NZ government.
Carlos, Does this Windtamer comply with any of the incentives offered by NYSERDA?
Bert, the WindTamer is not in the current list of 31 Qualified Wind Generators selected by NYSERDA for small projects. They might be in the process of qualification. Only qualified generators can be installed under this program according to the NYSERDA. Please, send me an email if you are interested in their URL. Happy Holidays!
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