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Conor

One of the GVCS tools is a wind turbine scalable up to 50kW. I'd like to throw out a basic design question: should this stand on a tower, or should we aim for a lighter-than-air machine that floats and is tethered to the ground?

Tethered wind turbines have some advantages: you can get them higher up, allowing access to higher winds; you can take them easily in case of adverse weather conditions, or for transport; you save materials and labor of building a tower; the noise the turbine makes won't bother you on the ground.

Disadvantages: it seems that you need a computer-control system to pilot the kite. This could be hard to design. Anyone know more about this?

www.ted.com/talks/lang/eng/saul_griffith_on_kites_as_the_future_of_renewable_energy.html
http://www.magenn.com/
http://www.kitegen.com/index_en.html

Allenman

Well if you had a Vertical Axis Wind Turbine, you could have it sitting on top of a tethered balloon. No need for any control system, because it doesn't matter what direction the wind blows; it will spin.

The problem comes when winds are too high. It could fry the circuits, possibly destroy the turbine, or even worse, break the tether and blow away. For that, you would need a control system of some sort: something to possibly land the turbine safely on the ground in case there was any such danger.

Sidnelsom

tethered turbines, if not controled by computers will need to be monitored by someone in case there is no more wind, or in the case of a storm. I imagine that someone in the middle of nowhere doesnt want to lose his source of power, mainly if its expensive to build. But still the tethered wind turbine is very interesting.

If someone want to build a tethered wind turbine, then it must be easier to build than a towered wind turbine, cause whoever used it will have to deal with the fact that they might lose it, and the towered wind turbine, in my opinion, would need less maintenance.

Occam's razor on that. Vote for the towered wind turbine.

Killer1306

I like the idea,

Have a cable (brake resistant), raped by a rotating spool of wire to transfer power to ground.

height can be adjusted to control speed, a little heating unit could be installed to keep the balloon aloft.

piolenc

This kind of proposal pops up from time to time in LTA (lighter than air) circles and elsewhere. A priori, it is feasible. Methods exist for transmitting power UP a tether cable and have been used for powering balloon-borne instrument payloads from the ground; no reason the reverse could not be done, though voltages would have to be high to carry the much larger power contemplated. There is a lot more engineering complication involved than just substituting an aerostat for a support tower. Support structure motion is less predictable, which means that the engineering of the turbine, its bearings and its controls will be more complicated, and as mentioned by other posters safety measures will have to be stricter and more elaborate than for a tower, since in the event of a tether break or damage to the aerostat the rig could fall far outside the area where it is operated. This is a development program, not a simple engineering option.

Daniel

A wind turbine like this one would be easier to make and maintain than a bladed one: http://www.silentwindturbine.com/design.htm
If you make each copy in a convenient size, perhaps 5 kW, so they can be made and assembled in the shop, then scaling up just means making more of them. You can probably stack several on a support tower for more power. Truss towers are fairly lightweight and cheap to construct.

Wolfrick

I've designed a system combining a balloon and several kites sharing a central sheaf of lines, generating mechanical power in a ground-based mechanism by transmitting traction via the kite lines.
This system is purely mechanical in nature, and is totally scalable from three kites up to many tens or hundreds at high altitude.
Since power is taken off on the ground, there's no problem of lifting electrical cables or generators etc.
What I need is more information about selecting an appropriate traction kite which can be deflated and self-reinflate. If you have experience with power kites, and want to help me, contact me directly via this forum.
~Rick

Daniel

Something I feel strongly about is "design for location". No single solution for a task like making electricity will work best everywhere. In a sunny location, solar will tend to outperform wind. In a cloudy but windy location wind generators will work better. The kite ideas above would work best if the winds at altitude are dramatically higher than near the ground. I don't know if wind profiles vs altitude vary much by location. Weather people and airlines would know. Then you could see if kites would work well everywhere, or only in certain locations.

Wolfrick

But no matter where you are, the wind does blow, and does blow harder the higher you go up.
I agree that solutions should be tailored to the individual situation.
But this kite system I've described is very flexible, very scalable, and potentially very cheap for the energy output.
But I haven't proven that yet. I need to demonstrate proof-of-concept.
Any way you slice it, a bunch of nylon cords and some ripstop nylon material is likely very much cheaper than glass and aluminum and silicon of a PV array.

Christoffer

Heres one simple idea for an aerial wind turbine with the generator on the ground. The "paddles" in the middle intermittently pulls the two wires as the turbine turn in the wind. I added support/lifting kites on the sides, i guess normal children kites that you can buy in a shop would do if you make the paddling center light enough. This would be a really simple underpowered one but it would be cool to test the concept. Its so simple that i imagine lots of other people thought of this too...

Conor

I've been looking into this a bit and it seems there are two basic designs: one is a turbine housed in a lighter-than-air balloon (see http://www.magenn.com ), the other is a generator on the ground with a kite tethered it, so that the pull on the kitestring spins a motor.

The kite design is pretty exciting for OSE purposes. The kite would cost a few hundred bucks at most, maybe as little as $15, and that just needs to be connected to an electric motor/generator, which is part of the GVCS anyway. The control mechanism is the only challenging bit.

ARGHaynes

In terms of general needs (http://openfarmtech.org/wiki/GVCS_Selection_Criteria) and all that expressed concerning the GVCS (http://openfarmtech.org/wiki/Product_Selection_Metric), where is this?

I'm thinking particularly about its applicability in forested or mountainous regions, places with pterodactyls and anywhere third-world.

That said, I think it is an amazing 'eventually' project.

Conor

It clearly nails every item on the list of GVCS Selection Criteria. The only exception is the last one; the fabric for the kite couldn't be produced by the other machines. However, I think this is trivial; it's just a few bucks of cloth.

It would fly well above treetops. Mountains would be an advantage. Pterodactyls are extinct. The third world really needs cheap ways of generating electricity.

Flipnash

quote by arghaynes "places with pterodactyls"

@ARGHaynes, woah! Did time just turn inside out or something.

ARGHaynes

@Conor I'm asking this because I don't know, not because I just like being a critic. Does the kite turbine meet the core needs better than a tower turbine? I'm curious why we don't see this much in most applications, but we see a lot of tower turbines.

Conor

Hopefully. I think it could potentially be cheaper: a few motors/generators on the ground, an Arduino plus an off-the-shelf power kite. There is no need to mill blades, which is the trickiest part of building a tower turbine.

But the real advantage is that a kite operates at a height of maybe 300m, while a tower-based turbine operates at a height of maybe 20m. According to http://www.kitegen.com/pages/winddata.html , global average wind speed is 3.3m/s 10m above the ground, 4.6m/s 80m up and 7.2m/s 800m up. That's a lot more power.

Conor

I drawed a picture.

The strings of a four-string power kite are attached to four electric motors (the GVCS motor/generators). When the kite pulls on the strings, it generates current, which charges a battery (the GVCS nickel-iron battery) (not illustrated). When the kite goes to the limits of its course, something detects that a certain amount of kitestring has been played out and an arduino tells the motors to reel the kite back in. Because there are four motors controlling four strings, you could get excellent control over the kite. A two-string version would probably suffice.

ARGHaynes

@Conor, thanks.

I'll have to research this a bit more before I respond again, lest I become my pet peeve (I phrase I used to think was French) and make a bunch of opinionated posts in an area where I am ignorant.

Conor

I'm just learning about this myself. To answer the question of why we don't see more kite generators, they're still a fairly new, embryonic idea, whereas turbines have a lot of history and investment behind them.

ARGHaynes

In the brief stretch of research I have done so far, I have been somewhat surprised to find that the idea is largely conceptual, I could not find any commercial kite-generators in existence at present.

VelaCreations

there is a great yahoo forum on this topic. The consensus appears to be that leaving the generator on the ground, and just tether the motion/kite.

I have seen a 1Kw system done like this. It had a rocking mechanism on the ground that change the angle of attack on the delta kite, causing it to rise and fall, pulling on a tethered line and generating power. It didn't have any mechanism for bringing down the kite in low winds or storms, but it seems a very simple start.

Dawg

I agree that the potential power is MUCH higher at altitude. But you know what they say about playing with fire....:) I just keep thinking of the liability issues surrounding an object that travels outside the property line. If that thing fell out of the sky and crushed some child on their way home from school there would be hell to pay.

I guess if you could make it so it would run itself and stay close to home then it might be worth it. Most people I've talked to who use wind generators say all they want "is the stupid thing to work". People get tired of constantly having to wrench on their stuff. Some are ok with much less output as long as they can count on it.

Any sort of flying generator is going to be a hand full I think.

The Dawg

Conor

@Dawg Yeah, that's why we are saying a kite tethered to a ground-based generator would be best

ARGHaynes

@Conor, I've been researching and come up empty-handed. Does anyone have examples of there being used by a community (or anything larger)? We are trying to use technology that exists to make something opensource, not create something totally new, right now it seems to me that this would be something totally new.

Dawg

@ Conor - So the generator will take energy from the tether being pulled out by the kite? Man you would need a big kite I think to pull hard enough to get any power out of it....no? As ARGHaynes said though, lots of R+D will have to go into that one.

The Dawg

Conor

>> So the generator will take energy from the tether being pulled out by the kite?
Correct

>> Man you would need a big kite I think to pull hard enough to get any power out of it....no?
Kites are powerful. They're powerful enough to pull a person and a surfboard at 30mph, so why not generate power from them?

It has been done before. Google 'wpi power kite' and check out the links I posted on the wiki page. There's a conference about it in a week: http://www.awec2011.com

Conor

Plans for a kite generator can be found on this wiki: http://www2.me.wpi.edu/wpi-kites/index.php/Special:Allpages

Studying these should cut months off development if we decide to take this on for the GVCS. The control mechanism, power conversion mechanism etc. are broken down into components and their functioning is explained. There's no bill of materials or build instructions, but it is incredibly useful information.

Here's a paper on the performance characteristics of the same system - http://www2.me.wpi.edu/wpi-kites/images/4/41/Asmees2008_54032draft.pdf
"The results showed that a one-kilowatt scale system is feasible using the proposed design concept with a kite area of 10 square meters and wind speeds of less than 11 meters per second."

Beluga

You can follow open idea incubation here: http://tech.groups.yahoo.com/group/AirborneWindEnergy/messages
Practical solutions don't exist yet and I think it would be a waste of time for OSE to spend time on AWE right now. Maybe take a new look at the state of the tech in 2013.
Faunhofer Institute is currently reviewing the AWE scene (no public info yet).

rodread

Oh My goodness. I am a regular contributor to the yahoo group. I am delighted to find you here. Check this out. http://kitepowercoop.org. Not conceptual any more. This is so the way forward. The low tech approaches of top and bottom valley tied systems are easy to implement. I'm totally into sharing my designs as open source hardware I was overjoyed to find this site. I have some interesting stuff on youtube too. http://www.youtube.com/user/roddyread?feature=guide
And if you're feeling really flush I have a pleasefund.us project for my current prototype. I love doing this and have not stopped smiling since my proof of concept worked. ACE

Beluga

Oh hi Rod! I guess I missed the funding launch. Well, here's the link for all interested readers: http://pleasefund.us/projects/daisy-kite-power-generator
Going to spread it now a bit..

Beluga

Airborne Wind Energy Conference 2012
http://www.awec2012.com/
Livestreaming as we speak and continuing tomorrow: http://www.livestream.com/awec2012

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