Ideas for scaling up AWES based on a tethered airborne rotor driving a rope drive

The downwind pull of the turbine is sure to bring the elevation angle close to ground, unless the lifter is relatively large

Tilting the turbine axis slightly upwards might help

1 Like

Doug, @gordon_sp hopes the download of his pdf document has worked!

Furthermore Gordon describes a vertical axis generator, not a VAWT as such. So the constraints are not the same. There is no rotor just above the described vertical axis generator. However the quote below suggests the opposite:

Indeed with a rope drive we have some “uneven tension” but it is negligible.
The advantage of permanent vertical axis generator by all wind directions remains.

I am talking about the weight of the rotor of the generator (rotor/stator).

Yes the thrust loading of the spinning rotor is a factor that can’t be ignored. It can be pretty strong. Also, many turbines tilt the rotor up a bit to avoid tower-strikes, which slants the shaft downhill to the downwind direction, adding to that sideways force on the bearings. At least in the “small-wind” turbine world, most models just use regular ball-bearings, which are not really meant to take much thrust loading, but they get away with it. Some of my tower-mounted SuperTurbines tilt upward so the downhill gravity thrust is counter to the wind thrust force.
One example of a vertical-shaft bearing problem is the oil-impregnated bronze bushings that the furling tails are mounted on can wear away after several years of operation. I’m rebuilding a 10-kW machine right now where there is almost nothing left of the bushings supporting the tail.

3 Likes

Why not use a horizontal driven pulley, supported on either end, and have the idler pulleys above the pulley? You can still then have you winding cage if you like I think.

Also you say in your configuration the idler pulleys are there to remove slack. I don’t see how that would work. They only have very limited travel to deal with any slack and if they do travel (down) they become misaligned with the driven pulley.

Beside the interesting study from @gordon_sp, the problem I see is the requirement of devices such like angle pulleys in order to assure a correct transmission from the tilted propeller of type HAWT. The more it scales the more weight penalty occurs. Moreover a farm of these devices would be difficult to manage due to the risk of collision with serious damage.

So the rope-drive can perhaps be more suitable for horizontal VAWT because it naturally assures both tension and transmission without supplementary devices. Moreover a farm of horizontal VAWT can be more easily managed, the possible collisions leading to minor consequences, as for AWES farm in bumper car mode.

An example is given on http://www.energykitesystems.net/0/Magenn/ , design by Harry Valentine:

Darrieus, Savonius (like for the design) and other horizontal VAWT could be used. In all cases the lower efficiency by unity could be compensated with both a higher use of the space and a simpler rope-drive transmission system.

1 Like

The bottom idler pulley redirects the cable to the power sheave. We are not trying to remove slack in most of the tether. We must remove the sag in the short distance between the idler pulley and the power sheave so that the tether does not rub against the wall of the sheave. If the idler pulley is located a few centimeters away from the power sheave, then there will be almost no sag.

Interesting, nice graphic, and it “works great” as long as it remains “on paper”. Savonius… something beginners can understand…
Level after level of loops: what could possibly go wrong? Ever had your chain come loose on your bike? And that is a fixed geometry, not floating in the sky, where everything could come loose in a downdraft.
This would appear to be a watered-down version of the old concept from the 1970’s, more recently renamed as “Laddermill”, which had already conceptually transitioned to SuperTurbine™ by the 1980’s. As in, this idea would naturally lead to laddermill, which leads to SuperTurbine™.


OK there is a picture of a couple of dust-devils here in the dusty desert. They happen everywhere, but because of the dust here, you can see them. It is rotating air. You see the central tube, but it is surrounded by a wide field of rotating air. All the windmills switch directions and lawn furniture goes airborne as they roll through. Wish I could show you the videos, which more clearly show the well-defined rotating tube structure, but they are too many Megabytes to e-mail out of my phone.

Here’s a picture taken the other day of a tree blown over on an otherwise calm day. Raindrops were falling when it happened. Not sure if it was a dust-devil, or a wannabe-tornado, or maybe some combination, but I was standing across the street and heard the CRACK as the tree was slammed to the ground.
How do you think such a stacked-savonius with multiple levels of rope-drives would fare in such a rotating airmass? How about a whole windfarm full of them? Maybe you could get paid to cart away the resulting debris. Maybe they could hold another auction!
:slight_smile:

1 Like

I believe that reorientation of the turbines to face the wind requires a frame which also supports the pulleys which direct the power to the cable drive. This frame can be constructed of carbon fiber elements which are light and strong. Adjacent trains of turbines can be connected together by lightweight carbon fiber struts which prevent the turbines from colliding. The philosophy here is to launch a single large turbine system rather than multiple launches.

I would add that said frame is also required to support several rotors. As the frame undergoes wind force on the rotors, its weight will be significant as the system scales.

Well done, Doug. I think that several rotors would also be difficult to use because they can come into contact with each other when the wind weakens and traction decreases. What about a single turbine, the rope-drive being within the side discs, each disc comprising a deep notch to receive said rope-drive?

5 posts were merged into an existing topic: Some talk about Dust Devils and Thermals

The “Laddermill” never worked, even without dust-devil.

The only way to see if laddermill works is to build one and run it, which, to my knowledge, nobody ever has. Then if one try did not work, it would still not disprove the concept. I’m sure some version could at least “work”, but how well, and for how long would be the question.

There has been some excellent recent testing by Hironori Fuji from TMIT
VFinal-kW九iMW fin.pdf (500.6 KB)

1 Like

Indeed it is a fine document.

I put in quotation marks the passages translated approximately from Japanese language.

The figure 2 represents a crosswind drone carrying a horizontal VAWT and with likely a rope-drive transmission. In the text: “By doing so, a basic study was conducted to aim for MW-class power generation”.

The figure 3 represents a horizontal VAWT suspended by a kite and also with likely a rope-drive transmission. In the text: “It is a 0.5 kW class wind turbine”; “Since this method is equipped with a wind turbine, It is capable of continuous power generation, small scale up to about 50 kW”.

The translation of the comments of the figures 2 and 3 is roughly:
“Figure 2: Ground-mounted generator with wind turbine (TMIT)”;
“Figure 3: Field test of a straight wind turbine with a kite hanging tether
(Generator installed on the ground/with wind turbine)”.

In the text of the second page:
“(3) Wind turbine (ground generator installed) type (W-Ground-Gen: With Windmill Ground Generator) Good performance as shown in Figure 2. A straight-blade wind turbine is installed on the UAV, and a tether is used to power the ground generator.”

I call as a “horizontal VAWT” what is named as a “straight wind turbine” by the translation.

Can you give a translation of some of the relevant points for those of us that don’t read Japanese?

Is there some new info since this: http://www013.upp.so-net.ne.jp/tmit/windpower/19Oct15AWEC3DTrajectory.pdf and does it talk about rope drives?

I admit to having renewed interest in the laddermill concept in light of some recent understanding in my part. I have to admit that my earlier comments dis not describe the full picture. Still not sure if I’m a fan though.

Operating a cable drive system in conjunction with a turbine system enables us to convert a flygen system to groundgen. The main advantage of this system is reduction of weight in the turbine system (no generator) and reduction in weight and cost of the tether (no electrical conductors). Because the system is much lighter, we can operate at much higher altitudes and capitalize on the higher wind velocity and more consistent winds. Variations in crosswind action can also be used to limit the maximum power output of the system in case of high winds.
The easiest way to operate with crosswind action is to convert the lifter kite to a power kite and operate in crosswind mode by means of a kite control unit (KCU). When the kite moves across the wind window either in a “lazy eight” or circular pattern, the turbine system will move back and forth and not tend to rotate about the tether axis. This rotation around the tether axis adversely affects the cable drive system. We can minimize this effect by attaching the kite tether to the center of gravity of the turbine system, and provide a swivel joint for a circular pattern. This method is essentially a Kitewinder system with a power kite. The cable drive has vertical pulleys (horizontal axis) with the high tension side on the top and low tension side below. The drive pulley (top pulley) is linked to the turbine system so that changes in the direction of the turbines will cause the same changes in direction of the drive pulley. The generator and driven pulley is floating and will naturally move from side to side to align with the top pulley (drive pulley). This is not true in the case where the turbines are an integral part of the kite (Makani). In this case the drive pulley rotates around the tether axis to match the lazy-eight or circular motion. With Kitewinder, the lower driven pulley is free floating and will move back and forth to match the top pulley and thus avoid the cable rubbing against the walls of the sheaves. Unfortunately, the drive pulley direction is directly related to the turbine direction, so when the turbine rotates to face the effective wind direction, the drive pulley will be skewed relative to the driven pulley. (Let’s call this the “cant angle”). This cant angle is significant. For example, if the crosswind velocity is 4 times the wind velocity, then the required cant angle will be 76° on each side. Without appreciable cant angle, crosswind action will be ineffectual. This cant angle makes operation of the cable drive ineffectual because the two pulleys are completely out of alignment. To counteract this we must realign the drive by means of carefully designed idler pulleys. Omnidirectional idler pulleys might be suitable to redirect the cable. Unfortunately scaling up this floating generator system might be very difficult because the weight of the floating driven pulley plus generator. Automatic operation of this system is also problematic.
An alternative method is my concept of a horizontal cable drive where the drive and return cable are in the same horizontal plane. This system must include 2 sets of omnidirectional idler pulleys (See drawing). The driven pulley and generator are anchored to the ground and the idler pulleys can freely rotate around the base to align with the top driving pulley.
Can anyone think of other ways to develop crosswind cable drives? I firmly believe that a cable drive system with a controlled lifter/power kite is easier to launch, land and automate than a Makani style system which requires onboard generators, batteries and/or inertial devices.
Crosswind Horizontal Cable Drive.pdf (70.2 KB)

I would like to summarize my thoughts on what I consider the most viable autonomous AWE system which can be developed. The Kitewinder system is the closest thing to steady state operation, depending only on wind speed. There is no variation in power output due to yo-yo retraction or variable forces due to crosswind action. Kitewinder is also the lightest system because there are no generators aloft or conductive cables. The cable drive is also used as the tether. This enables us to operate at higher altitudes where winds are stronger and more consistent. I also believe that we should use the turbines only for power generation and not lift since angled turbines diminish power and more lift can be achieved by a larger lifter kite. There is an advantage to using multiple small turbines because of increased power to weight ratio and the higher turbine speed results in higher cable drive speeds and lighter cables. Multiple turbines require a frame to secure them and orient them to face the wind. It is advantageous to have multiple counterrotating trains to neutralize transverse torque and prevent the a whole system from rotating around the cable drive axis. Kitewinder has a floating generator which may not be suitable for permanent installations. For this reason I recommend a fixed vertical axis generator with a horizontal driven cable drive pulley. In this way we do not have to move the generator when the wind direction changes.
With regard to autonomous launch and land, I have proposed a fully restrained kite with diagonal stays at the four corners. The kite is fully spread out at all times and when landed it rests on an LTA tubular frame. The kite is lifted to an adequate launching height and the LTA tubular frame is retracted. Alternatively a regular frame is lifted by lever-arm, telescoping arms or scissor lifts etc. It also occurred to me that perhaps we can eliminate the cable wind-up function. If the cable drive/tether is fully extended at all times, then perhaps we can launch the kite by controlled unwinding of the four diagonal stays. Landing will be the reverse of this procedure. With this method we can continue to operate the turbines for most of the time that the kite is being launched and landed.
AUTONOMOUS.pdf (86.7 KB)