I'm guessing: the same way you'd launch a regular kite: by starting with it off the ground and slowly letting out the line. Possibly the propellors can be switched from generators to motors if it needs an extra boost.
A balloon would lose too much in drag. If they can actually solve the software problem to get these things up and flying autonomously, it'd be pretty darn effective.
But I do wonder what would happen if the tether did break. It says that there are no batteries on the device, so if the tether is gone, is there any means of providing a gentle landing other than gliding blindly?
I'd say they have something worked out, as this is one of the more obvious catastrophic modes of failure imaginable. Of course, the unexpected is more likely to do harm - possibly the tether turning into a giant 200m steel whip ready to sever anyone unfortunate to be within the vicinity...
That said, I wouldn't mind one - maybe just a couple of KW for a rural off-grid section...
If this is true, it could be huge. Would these be deployable basically anywhere that is reasonably open?
I know some of the Makani guys and they are the real deal. These guys are seriously smart, and talented. I am glad everything is going so well for them.
Edit: You also need to transport that energy, so while much of the Midwest above average resources powering L.A. with that energy would would require a lot of new power lines.
Also, I'm fairly sure that the engineers behind this project are top notch and giving this project all they've got, it sure looks like they have picked some interesting challenges.
That said, I don't think this will ever 'fly' (pun intended) on any appreciable scale.
Wind is a fickle thing, and if you look at the design parameters of even the smallest windmills you realize that it takes bullet proof engineering to get a windmill to operate at all for any stretch of time without catastrophe, tying one to a kite seems to compound those problems to the point where even if the power generated were substantially higher than that on the ground you'd still be left with a higher per KW bill. Being able to operate in places where windmills are otherwise not viable is nice, but at 600 meters above the ground there will be substantial risk from getting kits entangled so the closest spacing will probably be such that a 'farm' of these will generate relatively little power for a given area of the planet over which the kites fly.
1 MW seems to be a pretty ambitious goal for a first setup, think about it, a 1 MW turbine sitting on the other side of a line will pull on the tether with a very impressive force, the kite will have to pull aloft a tether strong enough to withstand that force and up to 600 meters of power transmission cabling. These are not simple challenges. What I don't understand is why they don't build a 10 KW or so scale model and gain experience from that before going for a full MW, even a 10KW system flown for a year or two would give them plenty of experimental data to help design a larger one.
Then there are the liability issues, windmill towers are pretty solid and yet they've been known to fail. I figure the failure rate of kite lines+power lines would be substantially higher than that of a tower and so you'd have to contend with the occasional free flying kite+windmill combination.
All that said I wish these folks best of luck with what they're doing, but unlike the cheap solar panel revolution I highly doubt that this will ever be deployed at a scale large enough to be notable. Neat project though!
They seem to say that their wing tracing out the movement of the tip of a turbine, as well as operating at higher altitude will increase efficiency. They also have dynamic control systems to deal with variable conditions, increasing reliability.
As for your windfarm density reasoning, I think the vast majority of potentially viable land is currently unused, so achieving high density is not an issue now (although it might become one in future); there is more than enough land area to go around. Also they mention as a selling point of their system that it would be much more suited to deep sea locations than conventional turbines, opening up even more space for potential exploitation.
Concerning the need to build a scaled-down prototype, I think they mentioned somewhere that the pictures on their site are of a 10kW prototype :-)
About the liability in case of failure, they mention that they have implemented redundancy of systems on the wing itself, so in case of wing failure, it can still be brought down safely, and in case of tether failure, it can fly autonomously to a predefined location.
The only thing I don't understand is how they prevent the tether from getting all twisted up while still transmitting power through it (although I'm not a mechanical engineer, so there's probably a relatively simple solution to that) :-)
As I said earlier, I'm very impressed. This has got me excited.
The reason why I'm skeptical is because systems that are 'far out' in wind power have been proposed over and over again during the last decade each with even better on paper performance than the last one. Then as soon as a full scale model is tried it turns out the economies aren't there any more for some subtle reason (and sometimes not so subtle).
The wing tracing out the movement of the tip of a turbine makes the wing a turbine, there is no way around that, and as such it will be governed by the same laws, there are no exceptions from that. 1MW is not just 2 orders of magnitude more complicated than 10KW, it is probably more like 3 or 4. I've hand built a 2.5 KW machine, I'd be very careful to extrapolate my hard-won knowledge to a machine that is only 4 times as powerful.
For lower power levels a slipring arrangement is customary to avoid twisting up the cable inside a windmill tower, at higher power levels the mill is usually steered in such a way that the cables will not tangle.
I'm very curious how this will develop, I'm a huge fan of renewable energy but I've been around the awea boards long enough that I'd like to see some longer term results and at higher power levels before getting really excited. I do sincerely hope they succeed, time will tell, and google backing these guys is simply awesome.
I believe the generating curve is exponential, in that it isn't worth generating below a certain wind speed, which most locations don't reach. Just a little drop in wind speed can more than halve your generating power. Added to that, turbulence makes steady wind speed attainable mainly at higher altitudes, therefore requiring elevation (high towers)
Once you do have good generating capacity, what do you do when the wind is over the maximum threshold? A lot of older / smaller windmills need to be stowed during high wind, as they just can't cope with the amount of power developed.
Putting the windmills on a kite could indeed manage these issues somewhat - I'd imagine similar to sailing - where you can generate more speed than the wind provides, and possibly free-wheeling to dissipate excess speed / power.
Indeed an interesting area to watch!
That's very apt :)
> I believe the generating curve is exponential
It goes up with the cube of the windspeed
Most windmills nowadays (the grid connected ones anyways) are of the variable pitch type, which means they can run constant RPM up to a maximum windspeed at which they are shut down to avoid damage. Such high winds occur relatively infrequently though.
Freewheeling in a storm is not an option, a windmill that runs unloaded will quickly overspeed and fly apart.
For example, if the energy of the wind at high altitudes is tapped, the wind will (duh) lose its force. How will that impact weather systems?
Same for solar power - we'll be trapping radiation that will otherwise be reflected back into space. How does this affect thermodynamic equilibrium?
Same for geothermal energy - how does it affect deep-earth physics?
Maybe the effects in these cases are indeed linear in the small - like taking a drink from a river, but it is hard to be sure about whether they can be scaled with continued linear behaviour. Just as with fossil fuels ... one car probably didn't do much damage. 8 orders of magnitude later, its a different story altogether.
There will never be a windfarm that has a cross section comparable to a mountain range.
A mountain range isn't sucking the energy out of the system and sending into another one. The mountain range sucks the energy out of the air and transfers it elsewhere -- leading to the violent and unpredictable weather that large mountain ranges are known for.
Turbines suck the energy out of the air and don't put it back in the same place.
I don't think that we'll be able to draw enough energy out of the air to make more than micro-climate level changes, but then if you look at what's happening to the eastern Washington water table and the massive reservoirs on the Columbia River, the massive reservoirs on the Colorado, and so on, things start to look a little bit less promising.
Basically as far as I understand the general consensus, even when evaluating worst case scenarios, is that the amount of power that is taken away is negligible, even compared to the total power consumption on earth (i.e. even if all power on earth would come from e.g. wind power, that would still be only a minuscule part of the total power that is in winds blowing all day, or sunshine that is emitted by the sun each day.)
It's a neat idea, but do benefits outweigh problems?
The tip speed is what counts, the key governing factor is called the 'tip-speed-ratio', the apparent wind speed (as seen by the tips of the rotor) versus the real wind speed (as seen by an observer relative to the ground).
Almost all windmills that want to be efficient have design TSRs somewhere between 6 and 8, and consequently, in a given wind they all travel about as fast at the tips.
The design constraints are the speed of sound and the forces on the blade root as well as the tendency of the blade to start fluttering.
It has absolutely nothing to do with birds. Birds will fly in to a stationary building just as easily as they'll fly in to windmills, it's rare but it does happen every now and then.
The larger a windmill, the slower the blades will rotate.
The reason why they are so large is because the power harvested by a windmill goes up with the square of the rotor diameter, many small windmills are more costly to maintain and operate than a single larger one. Right now the sweet spot is somewhere around 2MW and 80 meter rotors for best $/W.
He was also scary smart and about as good of a mechanical engineer PhD as I have ever met.
Him being the CEO/CTO of makani makes a whole lot of sense.
Good luck, makani!
I'm a bit concerned about how to protect human lives around - will it be required to forbid access to a large area ?
The FAQ states that the peak altitude is 600 meter. Does that mean a circle with a radius of 600m must be protected ?
Pretty sure they thought of it already, it looks like a well thought out project, I'm just wondering.
EDIT: according to the FAQ, there are failsafes for both navigation and tether failure. It can even land itself untethered!
It looks pretty complex, but if the numbers work out right, this is probably the cheapest way to tap into the great winds available high in the sky.
http://www.makanipower.com/wp-content/uploads/2010/06/IMG_70...
EDIT: yup
http://www.makanipower.com/wp-content/uploads/2010/07/201006...
It's also funny Oregon has abundant hydroelectric power, but subsidizes these wind projects with rate hikes and taxes - while selling billions of dollars of these electrons to California at market rates.
http://en.wikipedia.org/wiki/Saul_Griffith
Saul seems totally awesome; his Long Now talk "Climate Change Revisited" was a fantastic survey of alternative energy solutions, and how no one was the answer, but that a cocktail of solutions is. His ability to put big numbers in context was stunning, especially his equating of industrial output in the US pre-WWII to the effort required to build wind turbines to cover half the usage of the current US electricity grid.
Here's the video of the talk: http://fora.tv/2009/01/16/Saul_Griffith_Climate_Change_Recal...
Overall it's an incredible step towards innovation in energy, kudos to the entire team.
Which is pretty awesome.
