Double propeller turbine produces 30% more electricity

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Developed at Lausanne Federal Technical College for use in helicopter and ship propulsion applications, the technology is also being applied in wind electricity generation. It might also be useful in improving the efficiency of other green electricity generation systems - eg tidal turbines, hydro electricity?

Video: http://www.youtube.com/watch?v=JrMQ1r2Kqc0

Newspaper article:

http://www.letemps.ch/Page/Uuid/0cd41b3c-0479-11df-82a3-9d622675a4b5/Une_%C3%A9olienne_%C3%A0_double_h%C3%A9lice

Company website:
http://eotheme.com/

ConsiderThis

I wonder does it affect the minimum wind speed needed to turn the turbine? I know in aricraft terms to have 3 or 4 blades on the propellor, as opposed to 2 blades, demands more power from the engine but gives better performance. I assume it must be the case that the "engine" here ( the wind) needs to have more power (speed) to turn the turbine?

Does anyone know?

McSandwich

ConsiderThis wrote: »

I wonder does it affect the minimum wind speed needed to turn the turbine? I know in aricraft terms to have 3 or 4 blades on the propellor, as opposed to 2 blades, demands more power from the engine but gives better performance. I assume it must be the case that the "engine" here ( the wind) needs to have more power (speed) to turn the turbine?

Does anyone know?

Most current wind turbines are designed to operate at high speeds. Three blades are typically give an optimal balance of strength and weight, while reducing noise levels.

More blades will take more energy from the same wind area/ volume (if available), producing more torque. This is not a problem for low speed wind pumps, but in high speed turbines it results in more stress on the blades and turbine mechanism. [edit] In reverse, a motor or engine would need more power/ torque to move the same air mass (as you said)[/edit]

Using current materials more blades would need to be lighter, and hence less rigid, to keep weight down. The linked design looks like it overcomes this by fitting the extra blades on a second propellor.

quentingargan

I may be wrong, but I just can't see this one working. Every time one blade passes another, there will be a shadow, turbulance and wear and tear.

One of the reason that mega turbines have three blades is because the wind is faster as you gain altitude, and at the top of its stroke, there is more force pushing the blade (and trying to bend the shaft) than on a blade at the bottom of its stroke. So one blade at top is balanced by two blades at 4 o'clock and 8 o'clock. Imagine the axial twisting that would take place when one blade passes another momentarily at the top of its stoke?

There are lots of innovations around and people trying to improve wind technology, and some of them will no doubt succeed, but this company has been around since 2003, but I haven't seen any of these around yet...