New company… its a rotary system too!
It looks like The Pyramid offshore version. The Tiira “ground-based carrousel beam” is tilted, just like the Pyramid “cartwheel”.
On the other hand the Tiira rotary device does not include “a triangular bridle between the kites” and has two kites instead of three kites for the Pyramid. But, in my opinion, these differences can be seen as options rather than main structural differences. Or it would be an evolution comparable to the evolution between Daisy and the Pyramid.
2 Likes
I agree the similarities with “The Pyramid” are striking. I think though, Tiira have been working on these maybe longer ago than my Pyramid presentation at AWEC, so I don’t mean to say they are influenced by “The Pyramid”, just that we both arrived at a similar conclusion.
2 Likes
In my opinion this is the most realistic AWE concept I have ever seen, including my own (which is not necessarily a reference) which all lead to dead ends.
The offshore aspect adds something to this AWES that really looks like something advantageous.
As this topic is part of “Company Development”, it would be interesting if it sparked this development.
Why not benefit from Kitemill’s rigid wing control experience, in order to move towards this rotating device project of Tiira via The Pyramid and Daisy, and gather respective knowledge?
From their website:
We are looking for:
- early investors
- motivated team members
- pioneering partners
Contact us:
Tiira Wind Power
c/o Simon Kober
Reichenbachstrasse 74
3052 Zollikofen
Switzerland
I just informed them that Tiira device is discussed here.
You need to forward that to Kitemills CEO/CTO…
1 Like
It’s done. All of this remains to be analyzed and to attempt to produce a small proof of concept to be tested onshore, with two small rigid wings, the “ground-based carousel beam”, control devices and an adapted software…
1 Like
Tiira, The Pyramid, Daisy, OTS and SuperTurbine ™ have a family resemblance. These tilted torque transfer turbines could be completed by the device represented on Makani patent US7847426B1, figures 1A, 1B, 2 and 4.
I wonder if a simpler control could be achieved by developing Daisy with rigid blades, keeping only the rotor and the tethers as airborne elements.
Otherwise some first tests could be achieved by using fast semi-rigid kites like the Celerator which is a really fast kite that I flew.
1 Like
1 Like
A video to explain how it works:
2 Likes
A fine test of another rotary device (here with three kites) was performed by @JS_Brouillon:
1 Like
I believe that Tiira and other “pyramid schemes” (excuse the terminology) not work because the tether is at a steep angle to the power wheel. Only the Component of the force in the direction parallel to the wheel is useful. This is only a fraction of the total force applied. This also applies to Daisy and MAR3.
You could say that as well regarding a regular horizontal axis wind turbine - only a faction of the force is useful
I agree that the design window is limited. But if you investigate, you will find that there are some potentially useful configurations. High lift to drag seems to be very important.
You could make the same argument about other designs:
- Yoyo AWE is not useful because reel out speed is much slower than a winch can handle (thus requiring very high forces, adding drag and mass to tether)
- HAWT turbines have too high downwind pull thus requiring a too large foundation to stabilize the tower
I am just adding these to describe the nonsense which is saying “it could not work” without putting in a minimum amount of work to see if the numbers add up.
I would advise you to read my short document about the Pyramid on TRPTSim/docs at main · tallakt/TRPTSim · GitHub
I do still think the triangular bridle is a very important component for such TRPT designs, a point where myself [The Pyramid] and Tiira diverge in opinion, though I am still on the fence until more experience has been shared in the open. (I am personally not pursuing any specific designs at the moment)
1 Like
@JS_Brouillon replying to one of my comments: “The “triangle” arrangement of the kite-to-kite tether also prevents the speed imbalances from making a mess.”
In some way, @Rodread 's Daisy achieved connections between the blades. So an alternate approach would be to supply a pitch control mean. I remember Daisy had a very good power coefficient (Cp) of 0.15 or 0.18, perhaps 0.2, and with a potential for improvement. An important advantage is the consistency, with the blades rotating at the same speed during each rotation, unlike crosswind kites which lose a lot in accelerations and decelerations, not to mention the risks of mess involved.
A TRPT could work like a solid structure up to limit heights.
2 Likes
I am just adding these to describe the nonsense which is saying “it could not work” without putting in a minimum amount of work to see if the numbers add up.
The following is a table of the percentage of power available with various angles of the tether to the power wheel. (based on cosine rules)
Angle tether to % Power available
Power wheel
60 deg 50%
65 42.2
70 34.4
75 25.8
80 17.3
I realize that the plane of the tether is not perpendicular to the take up reel and this complicates things, but nevertheless, I believe the above factors are the least damage that this phenomenon causes. I was unable to open up your GitHub report.
In addition, in all HAWE systems I have experienced there are cosine cubed, losses for tether angles, greater than 45° (Except kiwi.). This means that no systems can capitalize on to high altitude winds, unless extremely long tethers are used.
Corrected table
Open Power Angles.pdf (12.4 KB)
These are the cosines according to the angles. I did not notice any difference with the values given in the pdf. But as you know (see the quote from your comment below) the cosine losses are cubed. I am providing the rounded cosine values in decimal form for only angles of 60 degrees and 80 degrees to more easily give the values in cubed cosine.
Cosines for elevation angles of 60 and 80 degrees:
60 degrees: 0.5
80 degrees: 0.173.
Power after cosine cubed losses:
60 degrees: 0.125 (not much power)
80 degrees: 0.00517 (so almost no power).
AWE systems. HAWT = horizontal axis wind turbine. For the rest, see above, but to summarize, considering the power, losses are cubed. So what you indicate is true, excepted “In addition”.
Indeed the cubed cosine loss is applicable for all AWE systems, without any exception, even for Kiwee where the horizontal axis of the propeller corresponds to a cosine of 1 (for an elevation angle of 0 degrees), leading to an absence of cosine losses, whatever the angle of elevation of the lifter kite.
So there is a difference between AWES that carry a wind turbine and AWES that constitute the wind turbine.
A lot of AWES constituting the wind turbine work at a low elevation angle, 30 degrees for example. As the cosine is 0.8660, the power after cosine cubed losses is about 0.65: it’s a lot losses (35%) but still acceptable.
Essentially, I agree that Kiwee is a good option, and surely the best, and not just because of the absence of cosine loss (which is actually offset by the requirement for a relatively large lifter kite in relation to the greatness of the elevation angle of the said kite, which limits the advantage of no loss): the rope drive transmission allows for high lengths of rope while maintaining efficiency, unlike TRPT and similar like Tiira.
But tilted rotary devices, including Tiira, The Pyramid, Daisy, SuperTurbine™, could perhaps compensate with other advantages, taking into account that these devices are different each other.
What about tether angle losses? These losses are in addition to cosign cubed losses in a pyramid scheme. I feel the combination of these results are too extreme to make this project successful.
Concerning “tether angle losses” I do not see other losses than cosine cubed losses.
That said TRPT (including Tiira) geometries involve limits of torque transfer. They are summarized for Daisy (ground rotor parallel to the flying rotor, rigid transmission rings), for Rotating Reel, see figure 22.18 (ground rotor non-parallel to flying rotor, no rigid parts in the TRPT, little potential for height compared to the diameter of the ground station), see the calculations for The Pyramid - Engineering / System Design - AWESystems Forum, click on ‘here’ for the pdf.
Calculations are complex, but to summarize, the axial force (tension ensured by the TRPT and the lifter kite if applicable) must be high enough to allow the torque transfer in optimal conditions for a correct (?) but necessarily limited height.
Concerning TRPT including Tiira (no rigid parts in the TRPT), one of the parameters is the diameter of the rotating ground station, leading to the usable length of the two respective tethers of the two kites.