14 May 2008

Multi-Turbine Wind Turbines: Torque & Power

Multiple rotors on the same shaft can provide higher torque. Torque and power are related by the equation:

Inventor Doug Selsam has devised a way to put multiple blades on the same shaft, without having the blades interfere with each other's wind.
Of course, more rotors also means more-complicated physics. The key to increasing efficiency is to make sure each rotor catches its own fresh flow of wind and not just the wake from the one next to it, as previous multi-rotor turbines have done. That requires figuring out the optimal angle for the shaft in relation to the wind and the ideal spacing between the rotors. The payoff is machines that use one tenth the blade material of today’s megaturbines yet produce the same wattage. __PS_via__NextEnergyNews
Selsam is the type of inventor who is not afraid to go up against conventional wisdom. Even better, his ideas make a lot of sense.

The image at top is just an artist's conception. The shaft would not actually bend in Selsam's device.

A flexible shaft loses a great deal of power by flexing. If a shaft could be made that is both strong enough and light enough in weight to double as a "tether" and a multi-blade shaft, you may see attempts at multi-turbine "kite" configurations, or multi-blade lighter than air configurations, as suggested by the image at top.

Previously published at Al Fin Energy
Update 15May08:Here is a drawing of Selsam's approach. The generator is at the center of the shaft, balanced over the tower. The shaft is angled to the wind to allow each blade to catch its maximum wind allotment. Speed would be roughly the same as a small blade design, but torque would be almost ten times greater, hence more power. Power in a wind turbine is directly proportional to the square of the blade radius and to the cube of wind velocity. Although not a wind blade designer, I suspect the orientation of the shaft may invite some slight alterations in blade design.

Update 17May08: Actual photographs of the invention and inventor. In these photos, the shaft flexes downwards at the unsupported ends, while being supported in the center at a central generator by two bearings.


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Blogger Bruce Hall said...

Geometry tells me that the easiest way to have a shaft without complex gearing and multiple rotors is to have the shaft parallel to the ground and the rotor perpendicular to the wind.

This could be accomplished by supporting the shaft with a beam from the end of the shaft to the base of the tower. Additional support would be provided by intermediate beams between the the main support beam and the horizontal shaft.

Think of an inverted right triangle with rotors along the top leg and struts between the hypotenuse and the top leg.

Actually, depending on the height of the tower, you could have a series of inverted right triangles going up the tower... each with a set of rotors.

Thursday, 15 May, 2008  
Blogger al fin said...


I'll add a drawing of Selsam's concept to make it more clear how he proposed to keep each rotating blade out of the "wind shadow" of its more windward blades.

The thing that impresses me is the ability to trade off multiple small blades for the ultra-large blades and get the same power output. If you've seen a video of one of those big blades exploding from material fatigue, you get an idea why so many designers are experimenting with smaller blade designs.

Thursday, 15 May, 2008  

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