Tensile Rotary Power Transmission Model Development for Airborne Wind Energy Systems
poster by Oliver Tulloch @Ollie
https://www.researchgate.net/publication/344489825_Tensile_Rotary_Power_Transmission_Model_Development_for_Airborne_Wind_Energy_Systems#fullTextFileContent
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A wee thought on the benefits of rotary designs in offshore environments…
Offshore is where utility developers want to deploy.
Working out of sight, in good wind.
Weird thing is, despite offshore wind turbines having longer service downtime, they have higher capacity factor due to the better wind resource.
That good wind has very different AWES design justifications than onshore wind resource.
Over the land you want AWES working the high altitude to get your kite away from slow & low wind shear - great justification.
Over water however the wind shear isn’t so significant so designs which can deploy cheaply and start working from a lower altitude will have advantages.
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Indeed the expected low altitude of torsion-transfer rotary designs is not an issue thanks to a low wind gradient. However the most advanced rotary designs like Daisy or SuperTurbine ™ are in 1 kW range. And as an example the rotor diameter of the large gyroplane Fairey Rotodyne is “only” 90 ft (27.43 m).
An offshore turbine has to be in several MW range to be competitive. Some problems of weight can occur, preventing powerful rotation, a little as for Makani M600.
Couple points to straighten
A Fairey rotodyne compound autogyro with tip jet power… The rotors are far heavier for the same swept rotor area than kite turbine autogyro rotors.
Low altitude isn’t a necessity in kite turbine operations. See the work @someAWE_cb does with OTS. An amazingly long shaft.
Whereas Christof has highlighted the modular extensibility of TRPT (Tensile Rotary Power Transmission) We’ve been demonstrating the modularly extensible nature of kite turbine rotor stacking.
The problem Makani had of weight preventing tight rotation is resolved in kite turbine rotors which physically restrain blade sets onto a shared network path. The path is held in the power zone.
The cheapness of modularly extensible design lowers the mass costs of energy production. Therefore LCOE can be competitive from smaller systems… The bigger networks will be even better.
I took the example of the Fairey Rotodyne to show the limit of the rotor diameter of existing autogyros, regardless of weight. None of the rotating AWES has an equivalent diameter. That said my example is perhaps partially not correct because its rotor is completely rigid and in one piece, allowing balancing of the kinetic energy of the blades, putting aside aerodynamic forces, the acceleration by gravity of the blade going down being compensated by the deceleration of the blade going up, that by construction. But such a rotor would be too heavy for an AWE use.
It is the reason why I wrote about torque-transfer rotary designs that could be appropriate to fly at low altitude. Perhaps you thought about them. For what I know none of them reaches 30 m currently: even HAWT reach higher altitude, without talking about classical kites.
The problem can be identical with restrained blades if they are not in one piece, so very heavy, at least concerning a single rotor in MW range. For stacked rotors the problem could perhaps be mitigated, the price to pay being a difficult management of takeoff and landing operations.
The blade going down has a tendency to want to accelerate by gravity and produce more kinetic energy than the blade going up, excepted if the rotor is completely rigid and in one piece like that of a wind turbine or an autogyro. It is true that a rotor with several blades (even in several pieces and by an active control of each blade) could be better balanced than a single wing flying crosswind, but a AWE rotor is not held by a rigid structure like a tower, unlike that of a HAWT which in addition has a single-piece rotor allowing perfect balancing. Beside it I don’t know how is interference between aerodynamic forces and the weight and kinetic energy, for a tilted rotor whose what’s more the weight is not aligned: this is a point to clarify at MW range.
Perhaps using light flexible kites or blades can be a mean to scale more, as for other classes of AWES.
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This goes back to what I’ve been saying for over a decade.
You can read graffiti on an outhouse wall:
“Eat sh** - a million flies can’t be wrong”
Or like our moms said:
“If all your friends jumped off a cliff, would you do it too?”
(hang-gliding)
I have always maintained that most efforts “Don’t know what they’re doing”.
Now that notion could turn out to be wrong…
Or not.
I think it is charitable to call any AWE effort “commercial” considering the lack of commerce in AWE.
Anyway I don’t think there is any need to argue anything, to write long papers, anything. I say if you know what you’re doing just build it and sell it. Or sell the power. You don’t need other AWE fans to agree. Either something works or it doesn’t.
A quick analysis of rotating AWES shows that there are two kinds of arrangement with the generator at ground:
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Fully rotating assembly (SuperTurbine ™, Daisy, OTS, and the late lamented Rotating Reel System).
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Rotating assembly with fixed parts aloft (Kiwee, variants to develop (I am working on it)).
The former have the advantage of greater structural simplicity. The second allow a transfer by rope drive without rigid part in the transmission system.