Tuesday, 3 August 2010

3MW Kite generator in build ?!

World's most powerful kite turbine?

Just saw this video today featuring the Kitegen project on the Italian TV show 'Superquark'.

At about 2 mins 45 and 4 mins 50 you can see the system that featured in their last CGI animated visualisation in actual construction. Note that I actually have no idea if this actual build is supposed to be running a 3 MW generator, but this article on their website said that this was the case for the STEM concept.

Wow, at this point I should point out that Kitegen have been testing the largest capacity airborne wind energy system that I know of at 30kW for some years (data for auxiliary power generation capacity of the Skysails system is not available). They were the first commercial AWE project running if Skysails is discounted, and they have a considerable patent portfolio.
But... 30kw to 3000 would be an ambitious step. I'd love to know more about the motivation for the design concept, especially the rotating boom, which presumably would need active control, or at least damping to prevent its inertia taking it in an opposite direction to the kite at each extreme of the lying 8? Would a tower not be simpler? Also, it would be great to know what kite they are going to use, an 500sqm LEI doesn't seem particularly practical, and the L/D is not great. I guess we'll have to wait and see!

If any readers out there speak Italian and can glean more information from this than I have please enlighten us!

Sunday, 1 August 2010

Back to light entertainment, new Makani site, new companies, conference news

So after that painful exposuse to some math, here is something nice to look at, Makani's rather fetching new website . There's a new video I hadn't seen:

Which is nice to see, not sure what the wing area is, but you can see the power output and windspeed in the plot, if you managed to keep watching after that stomach churning on-board cam bit. I might do a post on the content of the new site at a later date.

Also here's a new company: Kitemill. I know not alot about this project but given the name I would expect ground generation with a kite? And another one : Altaeros Energies, who don't have a site yet but this article
shows a logo and the scheme of operation which is basically a windturbine elevated with a buoyant & lift generating, passively stable enclosure/fairing like this:

Final exciting news is that Jianjun Zhang of the snappily titled: Guangdong High-Altitude Wind Power Technology Ltd. will be at the AWE conference. I'm sure everyone is keen to hear about that project. Registration is open for the conference and I would definately recommend going. The list of speakers looks fantastic.

Ok ok, here's the last bit: Flygen vs Groundgen the finale

Has it really been 2 months? Sorry for the lack of updates, I have been desperately trying to bring my work together for my Dphil thesis which is due to be submitted in 53 days exactly and I'm still, hmm about 25k words and about 10 flight tests short!

Here is some of the ground gen/ flygen comparison brutally culled from my post on the awe list and from Loyd's wonderful paper.

Ok, some pros and cons. This is assuming that for a flygen you would have a hard wing and for a groundgen a soft wing. Uwe at TU Delft pointed out quite correctly that you can have a hard wing groundgen like that at Ampyx that will have some of the advantages  (and disadvantages!) of both approaches.

Soft Hard
Harder to get high L/d   Easier to get high L/d
Lighter Heavier - inertial loss?
Less prone to weight penalties on scaleup More prone to weight penalties on scaleup
Cheap Expensive
Subject to wear, esp when fluttering  Excellent wear characteristics
Under-actuated  Excellent control authority
Difficult and comp expensive to model- Multibody approach? Can be modeled through conventional techniques, i.e.Neuton/Euler or Lagrangian in real time
Pack down small  Don't pack down
Could deform to match conditions Must operate in all conditions
Can do ground gen   Must run power down cable
Severe cable wear from repetetive bending - if doing groundgen Cable bending frequency is low - if doing flygen

After that, here are some gems from Loyd:

Basically this is saying that the power scales linearly with air density but with the cube of the apparent windspeed. Translation: Going fast is dispropotionately rewarded, when going high air will be thinner but this should be more than cancelled out by faster wind.

Next....Speed, and hence apparent wind speed is going to be affected by the lift/drag (glide) ratio of the wing, less drag meaning more speed. According to Loyds analysis this is another exponential effect - check it out here for the drag(flygen) mode, where:

This graph shows the exponential scaling showing how important efficient wings are. It looks linear but the scales are logarithmic ok!

This next graph shows that the peak power of the lift(groundgen,Fc) and drag(flygen,Fd) modes are pretty much the same. Groundgen reelspeed wants to be about 1/3 of windspeed, and there is a broad peak for the flygens in terms of the ammount of drag you put on the wing, which gives a fair bit of operational leeway.

Now, Loyd does miss some things out for that comparison graph: tether drag: assuming that you have an unfaired ( a normal) tether, it will begin to dominate the drag of the system as your l/d on the wing gets higher and higher, so you won't see anything like the advantage shown by the graph.
Also Loyd assumed weightless wings.... why does this matter? Because during steering you are pulling the wing away from the direction it's is going, you will be using some of the energy from the wind for fighting the wings inertia. The heavier the wing the greater the loss.

Ok there ares a load of other things that could be incorporated to a model but that's enough for one day. So.. the conclusion is..... There is no clear winner, each approach has advantages and disadvantages, the 'best' solution won't neccesarily win the market, it will be a balance based on capital cost, performance, durability, safety, public acceptance, and more. In short, there's no free lunch.

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I finished my PhD on Evolutionary Robotics in Airborne Wind Energy applications in 2010. Since then I have been working in industry in the area.