Hacker News new | past | comments | ask | show | jobs | submit login
Makani Power, a Google funded wind energy startup, comes out of stealth (makanipower.com)
155 points by miratrix on July 18, 2010 | hide | past | favorite | 78 comments

Wow, where to begin. First off, I'm really happy that Google continues to fund energy related start-ups, their solar and wind efforts are commendable.

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!

I was ready to be all sceptical too, but I actually came away from the site quite impressed.

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.

Thanks for digging further, I read most of the site and I missed the 10KW prototype thing (it is the sensible thing to do, and I'm glad they did it).

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.

From what I remember, most problems with windmills are due to 2 factors: Not enough wind Too much wind

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!

> From what I remember, most problems with windmills are due to 2 factors: Not enough wind Too much wind

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.

"Makani AWTs will produce energy at an unsubsidized real cost competitive with coal-fired power plants, the current benchmark of the lowest cost source of power."

If this is true, it could be huge. Would these be deployable basically anywhere that is reasonably open?

In the "Fundamentals" section of the website (http://www.makanipower.com/concept/fundamentals/) Makani claims that their system can operate in 85% of the areas in the US vs. traditional windmills that need class 4 wind which is only present in 15% of areas in the US. Also there is some interesting info about why their approach could be better for offshore wind generation.

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.

Offshore wind generation seems to be an obvious win, although the materials will have to be tougher.

I suspect there may be some voodoo hidden in that term "real cost" -- i.e. it's dependent on some "cost" of CO2 emissions which they've derived ex anum.

No, even at altitude wind is fairly local phenomenon. As the price of wind power drops, more places become competitive with coal, but the best drip below the price of coal. http://www.windpoweringamerica.gov/wind_maps.asp

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.

Considering the miserable state of the US grid system new power lines have to be built anyway.

Is the US grid system really in that miserable of a state? It seems to work just fine where I live. And is the right solution really building more power lines? It's not clear to me why that would solve any potential problem with the system, other than that more power needs to be transported than can currently be. And if that is so, how do things work at all now?

The best places for generating (conventional) wind power in the US are the prairie states, and the best places for generating solar power are in the Southwest. But since both of these regions are sparsely populated, there isn’t very much grid infrastructure there—there is enough to bring power to the people who do live there, but not enough to handle taking power from a power plant to population centers farther away.

Also, if a substantial portion of our power supply is going to come from intermittently available sources, then the switching technology in the grid is going to have to be a little more sophisticated.

I'm fine with the idea that more lines would have to be built in the case of wind-power. That's not what I was questioning. I was questioning the claim that the US power grid is in a "miserable state" for current applications, which is a notion I see bandied about a lot with nary a citation.

Also would you please describe what about the switching technology in the grid is going to have to get better? Or cite some source that does so?

I think this is basically what people mean by “miserable state”. It’s not just more lines, but more very-very-high-voltage lines. Also, these lines are generally regulated at the state level: the government of Nebraska may not be exactly eager to authorize a high-tension swath being cut through its land just so that power can get from North Dakota to Texas.

Regarding switching technology, Technology Review had an article a while ago (http://www.technologyreview.com/microsites/spain/wind/) mentioning the wind-power industry in Spain: “Because wind is an intermittent resource, providing power only when it blows, the grid has to be able to cope with fluctuations and dips in electricity. When wind accounted for only a small percentage of the country’s power, such dips made little difference. But as this resource achieved greater prominence, split-second losses of power could have caused problems, especially since Spain doesn’t have strong grid connections with neighboring countries....” The article goes on to describe how the grid management system adapts to this problem.

OK, I still haven't seen any evidence that the US's system is relatively miserable. Am I not clearly asking for what I want? Articles about how Spain's grid system adapts to wind power don't do much to prove the point that I'm questioning.

The fact that the grid still works most of the time for most of the people doesn't proove that the grid is in good shape, in my point of view. Yes, it worked, and it still works. But the US missed to invest in its infrastructure - roads, bridges, water, just to name a few besides the grid - in the last couple of decades. This might be cheap on the short term, but it's going to be even more expensive in the future. The US has a critical investment deficite regarding its infrastructure, including the grid.

'In August 2003, the power failure that affected 50 million people in the United States and Canada was not caused by a single extraordinary event on a single system, but rather a series of routine events that quickly became unmanageable because of an aging electricity distribution system lacking redundancy. National laboratories and others that have evaluated the weak points in our energy infrastructure have identified similar scenarios where a seemingly modest, routine occurrence can cascade into a debilitating energy supply disruption in very short order.' - http://www.energyxxi.org/pages/Blueprint_Modernize_and_Prote...

> The fact that the grid still works most of the time for most of the people doesn't proove . . .

That's not what needs to be proven. The opposite does. The default assumption is that something that works is working. It's the responsibility of those who disagree with that point of view -- those who claim that the grid is underdeveloped -- to prove that it's broken.

> But the US missed to invest in its infrastructure

By what metric?

> This might be cheap on the short term, but it's going to be even more expensive in the future.

That's not how these kinds of things usually work. Usually the longer you can put off an upgrade, the cheaper it is to maintain a system when you amortize it. And I can't see why this would be any different in the grid (or roads, or whatever else).

> [Your quote from the Institute for 21st Century Energy]


* doesn't cite any sources, and * is a lobbying group whose members stand to benefit financially from me accepting their claims uncritically.

Which means that the last thing I am going to do is accept their claims uncritically.

>> But the US missed to invest in its infrastructure > By what metric?

I'm not a civil engineer, and I don't know if anybody can tell reliable numbers at all for that issue. But the US infrastructure hasn't received proper maintenance in the last decades if one can trust certain studies. And this is getting serious for some areas in the next couple of years.


Looking at the downward trend for most cathegorized domains since 2001 is not a good sign for US infrastructure. One may say that everybody involved in that business has his own interests (government(s), construction businesses, consultancies i.e.) and is trying to defend them or make profit out of certain decisions. But stretching the infrastructure to the upper limit of the designed lifetime without proper maintenance until then just accumulates infrastructure investments, mostly towards a higher figure. (It's always difficult to find reliable sources regarding that issue, with a lot of lobbying going on in that area. In that case I simply trust the American Society of Civil Engineers for judging about that issue because my own lack of knowledge and expertise.)

> That's not how these kinds of things usually work. Usually the longer you can put off an upgrade, the cheaper it is to maintain a system when you amortize it. And I can't see why this would be any different in the grid (or roads, or whatever else).

It's not only about the equipment working until or even over the designed lifespan and/or just replacing them, but the aging grid is characterized by a couple of points. There's an interesting book called 'Aging power delivery infrastructures' from Willis et al. (2001) about it: http://books.google.com/books?id=1GcxSDpvdzYC

Basically in that book the authors point out 5 main factors: 1. Old equipment, 2. Obsolete system layouts, 3. Old engineering methods, 4. Uncoordinated and non-optimal use of distribution, 5. Old cultures and ideas.

I think there hasn't been any major improvements since the release of the book, at least no I'm aware of. And this is definitely not an US-only issue. But I think there's definitely a need of rethinking and reengineering the power grid.

It will be a big effort for western industrialized nations to bring the grid, which is mostly pre-70's, into the new century. And just by pushing the lifetime of this old and inefficient grid doesn't make it cheaper (higher failure rates, inefficient equipment, blackouts, i.e.) in the future.

I read in Perfect Power, that the average age of major step-down and step-up transformers is over forty years and that they were only rated for forty years. Ditto for the high voltage transmission lines. This infrastructure cost something like 550 billion to install and would cost over two trillion to replace.

You hit the nail on the head with your "over two trillion to replace" number: why replace them if they are still working? If expected cost of failures (probability of failure * number of things that could fail * cost of failure) is lower than the cost of replacement, it would be stupid to replace them. I will consider it a resounding success if these old transformers are still transforming away forty _more_ years from now.

Well, a few things come to mind: The utilities have customers, most of whom should expect that the utility will do what they can to avoid power failures, not just sit around and wait for them to happen. Also, apparently, the quality of power is pretty poor; lost of surges and unclean waveforms. Finally, the grid is unsuited going forward for more local and regional power generation (microgrids), because it was built for giant bulk power providers to transmit power over long distances, which made sense fifty years ago, but not as much today.

All of this is from Perfect Power. I'm trying to sort out, myself, how much of this is hyperbole on the part of companies with a stake in re-making the electrical power industry, and how much is legit (carbon tax/credits come to mind as potentially illegitimate).

> The utilities have customers, most of whom should expect that the utility will do what they can to avoid power failures, not just sit around and wait for them to happen

Obviously if the equipment were unsafe or likely to fail frequently, it should be replaced. I have yet to see this demonstrated.

> Also, apparently, the quality of power is pretty poor; lost of surges and unclean waveforms.

I don't think I know anyone who would be willing to pay more on their bill in order to get cleaner waveforms.

> Finally, the grid is unsuited going forward for more local and regional power generation

Is that really true? I know that in many places in California, it's possible to put power back into the grid and get paid back from the utility company.

It's miserable. The fact that it works (usually) just hides the fact that it's fragile and very leaky.

A friend of mine who does large-scale systems designs (he designs power and cooling systems for little things like international airports and the Gates Foundations new buildings) once said that our current power lines sacrifice close to 30% of the energy that they're supposed to be transmitting. By any rational measure in this day and age, that alone qualifies our grid as "crap" already, but the fact that a software bug shut down most of New England for several days three or four years ago doesn't cast any positive light on our pitifully outdated infrastructure.

> A friend of mine who does large-scale systems designs (he designs power and cooling systems for little things like international airports and the Gates Foundations new buildings) once said that our current power lines sacrifice close to 30% of the energy that they're supposed to be transmitting.

"Transmission and distribution losses in the USA were estimated at 7.2% in 1995 [13] and 6.5% in 2007[14]. In general, losses are estimated from the discrepancy between energy produced (as reported by power plants) and energy sold to end customers; the difference between what is produced and what is consumed constitute transmission and distribution losses."


My physics is getting a bit foggy, but I'm pretty sure I remember a lecture in which we were told that 30% transmission efficiency is actually about the best we can achieve with current materials science (without going to insanely expensive exotic solutions that don't scale or require non-room-temperature conditions).

This is part of why the idea of switching from big centralized power-plants to small localized plants is a big potential win.

I used to live in a co-op with Corwin (the CEO/CTO). The main thing I remember about him was that he was really into kite surfing.

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!

Interesting, when I saw the video I was immediately thinking it must have been a kiter dreaming up this contraption ;-)

This looks pretty interesting. They have some nice explanations of their concept- particularly the fundamentals link: http://www.makanipower.com/concept/fundamentals/

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.

It's an interesting idea (more wind higher up, without the expensive tall shaft required for a regular wind turbine), but how does it get relaunched when it falls to the ground? Wouldn't a balloon or regular kite be simpler and just as effective?

how does it get relaunched when it falls to the ground?

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.

Why guess when the answer is clear on the second frame of http://www.makanipower.com/concept/makani-m1/ ?

I thought the drag could be beneficial in a way similar to wave power generators: pull on the balloon would operate a hydraulic piston, etc.

The website clearly shows that the wing draws power to use its turbines as propellers when launching the wing.

I would imagine that the same principle may be used in slightly fickle winds, so that it could throttle back or even go back into propeller mode during fickle winds.

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...

This was on the Discovery Channel last night, currently(or as of the taping of the show), you need somebody with a remote control to fly the kite. They said they were working on making everything autonomous - which will most likely be one of the more difficult challenges for this project.

On the discovery show, it seemed pretty loud too. An annoying buzzing sound...not sure where they're planning on deploying these, but noise pollution might be an issue, not to mention potential crash safety issues.

Check the FAQ. It has the same noise level as a wind tower, which is already pretty quiet, but at a higher frequency and higher up, so the sound will dissipate more.

The noise info presented in the FAQ is pretty useless - noise from conventional wind turbines depends on wind speed, hub height and distance - saying that the level from the AWT is "consistent with conventional wind turbines" is meaningless.

It may be that they haven't done any noise testing at this stage (and the IEC 61400-11 standard for wind turbine noise testing is really not applicable to the AWT configuration) but they would have been better off just saying something like "we'll get back to you on that" rather than setting up expectations that might turn out to be unrealistic.

Yes, it's not just the volume of the noise, it's the nuisance: constant buzzing noises (especially high-frequency ones) are much more annoying than random 'household' noises, even if they are not as loud. I would have thought though that for safety and commercial reasons the wind farms would be built some distance away from population centres.

This post suggests they have autonomous down: http://www.makanipower.com/2010/06/wing4e-test-june-18-2010/

Ah, that's a neat movie. I don't know why it isn't on the front page of their website.

Still, the fact that they've got it working once doesn't mean the problem is solved. You need it to work all the time, in all sorts of weather conditions, and automatically stow itself if conditions become unsafe. Failure means plowing into the ground, which is probably going to be expensive each time it happens.

I'm sure they'll never get the plow-into-the-ground rate down to zero, but there's gotta be a lot of work still to be done to get it as small as possible.

It seems like they switch from manual to autonomous once they're at altitude: http://www.makanipower.com/technology/control (page 2)

The anser to the FAQ "Will this harm birds or bats?" was obviously crafted with the careful help of a PR and Legal team. :-p


The contrarian in me has always been curious about how tapping "eco friendly" energy sources impact the environment. (Any here have some serious pointers?)

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 is an easy way to see why this would not happen. A mountain range is a pretty sizable obstacle to the progress of airflow. It affects the weather directly around the mountain, and as much as 50 miles before the mountain and after it. But that's as far as the influence extends, and you'd need some pretty good data gathering and analysis to prove that. The effects that you can actually feel with your senses usually don't extend more than 10 miles or so beyond the mountain in the leeward direction, upwind you'd be hard pressed to notice any change at all.

There will never be a windfarm that has a cross section comparable to a mountain range.

That's not a good answer here.

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.

You are missing some basic stuff here. A mountain range is more, not less effective at 'sucking energy out of the air', it's basic physics. A windmill can only oppose the wind so much before it fails to work (see Betz' limit), a mountain range can suck 100% of the energy out of the air as you word it by simply converting the energy in the air to heat on impact (that's simplified but that's a good part of it).

As to your choice of words, turbines don't 'suck energy out of the air', they slow down the moving air. A mountain range does the exact same thing.

Read my post again. I did not say "mountain ranges don't suck energy out of the air."

BTW, turbines don't 'suck energy out of the air', they slow down the moving air

Those two statements are identical. Slowing down is sucking energy out of it.

This has been brought up since the first wind/solar/tidal energy plants were being brought in production. I don't have any links at hand but this has been studied; watch the comments under stories like this one, they come up often.

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.)

This is an incredible idea and an amazing feat of engineering. I'm sure they'll face huge challenges in deploying this thing but it just shows that real engineering is still alive. Damn, makes me wanna break out my fluid mechanics textbook :).

This looks way better than than the giant fixed turbines they are putting in Eastern Oregon which cost $2.4 million a pop, interrupt the view, and can't pay for themselves.

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.

I thought this was Saul Griffith's startup, but I see no mention of him on the about page. At his Long Now talk last year, I recall him talking about Makani as being his new effort.


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...

Joby Energy is another company in the area working on this problem. http://www.jobyenergy.com/

This idea has been batted around for a while and in fact the biggest risk to getting a project like this aloft will be regulators like the FAA.

The concept looks amazing!

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.

There is so much flexibility in where these can be deployed that you would probably never find them near a populated area anyway, just for economic reasons. They can also be deployed at sea much more practically than a tower turbine.

EDIT: according to the FAQ, there are failsafes for both navigation and tether failure. It can even land itself untethered!

Since this is a hacker site, any control theorists in the house? From observation and experience, controlling a tethered airplane is the most pressing technical challenge facing the team right now. Anyone ever modeled the dynamics of a glider or a turboprop?

They are mentioned on Discovery Channel's Powering the Future. I believe it was Saturday's episode. It has interviews and demos. No mention of Google but they do say they feel their problem is control systems for the kites, not the actual energy generation.

The only question I have is: how does it deal with harsh weather? Especially with offshore setups where storms are frequent, can it handle high winds and strong waves?

Overall it's an incredible step towards innovation in energy, kudos to the entire team.

Hope Google also invests in solar powered http://www.bogolight.com/ProductDetails.asp?ProductCode=BOGO...

What happens when the wind stops blowing or changes direction?

It lands! (The tether gets it done, and the rotors also back up as engines)

So, uh, a bunch of my friends are working on this:


Which is pretty awesome.

If they can make it work, this could be perfect for powering ships, too.

So, does the M1 produce 1 MW on average, or peak?

1 MW is the rated capacity. The actual amount of energy produced depends on where it is deployed. They go into detail about how much energy is produced on the "fundamentals" page:


So... do they makani power?

Rotors are tiny compared to conventional wind turbines. Even with six of them, just no comparison. Sure they harvest the wind much higher and it flys in circles quite fast, but I'm not quite sure how they'll be able to generate 1MW with on of those production things. It has the wingspan of B737!

It's a neat idea, but do benefits outweigh problems?

I was under the impression that most of the reason conventional wind turbines are so huge is so they can have the blades move slowly, to be more hospitable to local birds.

That impression is completely wrong.

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.

The reason why they are so large is because the power harvested by a windmill goes up with the square of the rotor diameter

Doesn't the Makani wings get around this issue by equivalent to a turbine with a massive wingspan and a wingtip that generates power, but without the rest of the structure?

The outer third of the blades account for roughly 60% of the total power generated by a windmill, the 'massive wingspan' would have to be normal to the direction of the wind, in order to say more about what Makani does or does not do there would have to be a lot more design data available than there is now.

Windmills with 'just the tips' have been proposed and constructed, there are some good reasons to include the blade all the way to the root. Part of that is to stem vibration, also to help with rotor start-up and low wind conditions.

It is normal to the wind direction, that's clear on the site. From the way you're talking it doesn't sound like you bothered to even look at what they're doing.

my nephew got recruited by a similar wind startup.


Looks like they're still some time away from having a working prototype though.

This will not work. It uses too much space and It looks like it will need repairs or at least maintenance all the time.

Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact