
Why Wind Turbines Have Three Blades - rfreytag
http://www.cringely.com/2016/05/06/15262/
======
Cerium
Three blades is the smallest number that reduces the vibrations due to the
blades crossing the support structure. When a blade crosses the support its
applied force is reduced because the wind is slower around the support. This
reduction in forces creates a yawing torque that can lead to unwanted
vibrations. Much of the structural stiffness and bearing requirements are
related to these effects. Three blades minimizes the effect because when one
blade crosses the support the other two blades are out in a Y shape,
shortening the force differential when compared to two blades.

~~~
mark-r
There's a question then, why are support towers solid? Maybe they should be
made more like the Eiffel Tower?

~~~
jacquesm
Because a lattice tower has much worse properties when it comes to interacting
with the wind. The behavior of the air behind the rotor is as important as
getting quality air to flow through the rotor.

Some early windparks used lattice towers, and some of those survive to the
present but they are now known to be worse performance wise than tubular
towers.

~~~
logfromblammo
A Shukhov tower [0] has minimal wind loading, due to its hyperboloid sections.

[0]
[https://en.wikipedia.org/wiki/Shukhov_Tower](https://en.wikipedia.org/wiki/Shukhov_Tower)

~~~
jacquesm
That profile is not very well suited to having a windmill on top of it. The
problem is that the nacelle is tilted backwards only a few degrees so you need
a very slender tower (or you'll have tower strikes in high winds).

~~~
logfromblammo
The cooling towers of a nuclear plant follow the same principle. The sides are
formed from straight structural members angled in opposite directions (doubly
ruled), and the gaps are filled with concrete.

The profile of a hyperbolic wind tower may be altered such that the cross
section at maximum height minus blade radius is at a minimum. The largely
conical profile of the existing Shukhov towers were used for power
transmission lines and a radio broadcast antenna.

Check this out: [http://www.pbs.org/wgbh/nova/next/tech/proposed-
hyperboloid-...](http://www.pbs.org/wgbh/nova/next/tech/proposed-hyperboloid-
energy-skyscraper-uses-simple-math-to-solve-a-big-problem/)

~~~
jacquesm
Interesting! You'd think that the major wind power manufacturers would have
looked at all possibilities. One major immediate concern is that these look
quite ugly and fat compared to the relatively thin and slender supports that
the latest generation of turbines uses. I'd love to see a side-by-side
comparison of these towers and the various alternatives.

[http://cache1.asset-cache.net/gc/78480146-crowley-ridge-
wind...](http://cache1.asset-cache.net/gc/78480146-crowley-ridge-wind-power-
alberta-canada-
gettyimages.jpg?v=1&c=IWSAsset&k=2&d=wW%2BWqJ5Jns5%2FhtycaQeRKiwHOo%2B1W%2FQabqSCG%2F1%2FRWnbLBlDKuH8j9bn4OWw4zSv)

Is one example of lattice towers in production that I know of (but not like
the ones you describe and I have never seen those being used for windmills).

~~~
logfromblammo
As mentioned in Jobs quote near the top of the article, you often find that
people tend to do things in a certain way just because that is what has been
done before. No one bothers to experiment because the old way has always been
good enough.

This is why is is sometimes difficult to avoid premature optimization, because
post-maturity optimization tends not to happen, even when it may be warranted.
I know of no wind farm anywhere that is used for side-by-side comparisons of
wind turbine technologies. It would very likely have to be owned by a
university and supported by public funds.

I have never seen a hyperboloid lattice or diagrid structure in person, but
they are not entirely unheard of for shapes that do not require a lot of space
efficiency in the tower portion, such as for lighthouses, observation decks,
water towers, radio towers, etc.:

[https://en.wikipedia.org/wiki/Adziogol_Lighthouse](https://en.wikipedia.org/wiki/Adziogol_Lighthouse)

[https://en.wikipedia.org/wiki/Kobe_Port_Tower](https://en.wikipedia.org/wiki/Kobe_Port_Tower)

[https://en.wikipedia.org/wiki/File:Ciechanow_water_tower.jpg](https://en.wikipedia.org/wiki/File:Ciechanow_water_tower.jpg)

[https://en.wikipedia.org/wiki/Corporation_Street_Bridge](https://en.wikipedia.org/wiki/Corporation_Street_Bridge)

[https://en.wikipedia.org/wiki/Aspire_Tower](https://en.wikipedia.org/wiki/Aspire_Tower)

[https://en.wikipedia.org/wiki/Canton_Tower](https://en.wikipedia.org/wiki/Canton_Tower)

~~~
hueving
>No one bothers to experiment because the old way has always been good enough.

If you are a manufacturer though, you have all of the incentives to come up
with something more efficient though. Wind turbines aren't controlled by a
monopoly are they?

------
scblock
This is only partially related to my other long post here, but it should be
mentioned. This article appears to be largely about potential to disrupt the
wind industry with outside the box thinking. But in the more than a decade I
have been working in this industry the single most disruptive change in
project performance was targeting low wind speeds rather than high, and
accepting that turbines will have to shut down in higher winds.

The main way this is achieved is to take a huge rotor and put it on a small
generator. More energy is lost at high winds, but the ramp up from no
generation to maximum is much faster. Since most projects spend the majority
of their time along that ramp rather than at rated power this results in large
gains in annual energy.

This means that some sites once considered to be marginal to end up being good
to very good. One area I've been working in saw a more than 25% increase in
predicted energy for the same capital cost with the new turbine types.

~~~
Grishnakh
I'm not in the wind industry and am not a ME, but rather a EE, but why
couldn't you build a big vertical-axis wind turbine and then couple that to
multiple generators, a big one and a small one, with gearing that lets the
windmill drive either one? Then in low winds, you can drive the small
generator at its optimal speed range, and then in high winds, you can switch
over to the big generator and drive it at its optimal speed range (the small
generator is decoupled in this mode).

Obviously, this would be much more costly because of the additional big
generator and the complication of the drivetrain. But it'd let you harvest a
bunch of energy when it's really windy. And with a vertical-axis mill, not
only would this be better for wildlife (lower overall speeds), the generators
would be on the ground, not way up in the air, and driven by a shaft from the
mill through its tower, so servicing would be easier and the weight and size
of the generators and the drivetrain wouldn't be an issue.

~~~
brandmeyer
I think you've misunderstood the innovation. The innovation in using a
generator that is smaller than the blades and tower are capable of supporting
isn't in the light-load efficiency of the generator. Its in the lower capital
cost of the electrical system.

------
mapt
* I don't understand his explanation of starting torque. You can jump-start that problem by other means in the alternator. Torque and power should be decoupled anyway by blade pitch.

* There is such a huge difference between a 12m blade and a 60m blade that I don't see how the comparison is at all relevant. We played with smaller turbines for _decades_ before we reached this sort of price efficiency.

* Betz' law explicitly disavows picking a number of blades: "Assumptions: 1. The rotor does not possess a hub and is ideal, with an infinite number of blades which have no drag. Any resulting drag would only lower this idealized value. ..."

* Betz' law is a three-dimensional consequence of convervation laws, not an observation about turbulent blade interactions. "Consider that if all of the energy coming from wind movement through a turbine was extracted as useful energy the wind speed afterwards would drop to zero. If the wind stopped moving at the exit of the turbine, then no more fresh wind could get in - it would be blocked. In order to keep the wind moving through the turbine there has to be some wind movement, however small, on the other side with a wind speed greater than zero. Betz' law shows that as air flows through a certain area, and when it slows from losing energy to extraction from a turbine, it must spread out to a wider area. As a result geometry limits any turbine efficiency to 59.3%."

* We already have a good idea what a moderate redesign of the fundamentals of a wind turbine looks like; It points downwind, it's huge like the existing turbines, and its two blades bend. They just need to solve the tower strike problem. [https://www.technologyreview.com/s/401583/wind-power-for-pen...](https://www.technologyreview.com/s/401583/wind-power-for-pennies/) [https://www.technologyreview.com/s/528581/two-bladed-wind-tu...](https://www.technologyreview.com/s/528581/two-bladed-wind-turbines-make-a-comeback/)

~~~
brandmeyer
> I don't understand his explanation of starting torque

That's because Cringley doesn't, either. The starting torque is entirely
provided by the wind, not the grid.

~~~
beat
I think what he's talking about (not bothering to re-read) is the power
required to magnetize the alternator components in the first place, so the
alternator works at all. They use electromagnets rather than permanent
magnets, because electromagnets are much cheaper, especially at that size.
This is a fixed power requirement, so if the alternator can't generate more
than that fixed power need to operate, there's no point in running.

~~~
brandmeyer
Magnetizing power (and other constant-term losses) are a very small portion of
the rated turbine power in a doubly-fed induction generator (DFIG).

Edit (one more thing): At this scale, permanent magnet (PM) machines aren't
much more efficient than DFIG machines. It turns out that eddy current losses
in the stator back iron remain as a significant term in both machines. But for
a DFIG machine, the eddy current losses at light load are reduced by quite a
bit relative to the losses produced by a PM machine. Since real-world wind
turbines end up operating at partial load for much of their life, the effects
basically wash out, or are even a net negative for the PM machine.

------
calinet6
This is a classic example of sub-optimization (and even if it's hand-wavey
pseudo-science and may be wrong, the general concept is still interesting).

Each individual wind turbine is optimized to be the "most efficient" it can
possibly be.

But not in the context of the environment, which requires complex control
systems and methods to reduce damage in non-optimal conditions.

And not if you take cost and efficiency of the whole system into account;
where four times as many small turbines with less complexity run more often
and produce more overall output.

But hey, each wind turbine is "optimal." Interesting.

Most complex systems have this property. Even (especially?) your business.

~~~
nkoren
This kind of thinking contributed to American rocketry being trapped in a
local maxima for decades. There are many reasons it became trapped, but one of
the primary reasons was that rocket scientists would insist on optimising
rocket engines at the expense of every other aspect of the vehicle.

"The logic of rocket equation is brutal and inexorable", the NASA rocket
scientists would say. "As the performance of the rocket engine decreases
linearly, the propellent requirements increases exponentially. Therefore it is
imperative to have the highest-possible performance from your rocket engines.
The combustion of liquid hydrogen / oxygen is the highest-efficiency chemical
reaction, and therefore liquid hydrogen is the only propellant we will
consider using for our engines."

All of this was correct, but also _wrong_. It was wrong in a whole-systems
context, because:

A.) Liquid hydrogen is much lower-density than traditional rocket fuels like
Kerosene, requiring far larger and heavier structures to carry the same amount
of energy, and larger and heavier engines and plumbing and everything else --
and the structural mass of a rocket _matters_.

B.) Liquid hydrogen will boil off and leak through anything, requiring massive
amounts of insulation (again, adding weight), and far stricter operational
protocols around the fueled vehicle.

C.) Liquid hydrogen is so cold that it will embrittle and shatter ordinary
metals and requires much more exotic and expensive metallurgy.

and finally, D.) The alternative, kerosene, gives you less efficient engines
but also much lighter-weight vehicles -- and sure, per that inexorable logic
of the rocket equation, you need to use more fuel for the same amount of
payload, but kerosene is _cheaper than milk_ so who fucking cares?

Anyhow, the upshot of this is that US rocket scientists spent literally tens
of billions of dollars developing hyper-locally-optimised rocketry schemes,
most of which failed outright. For the remainder, for every dollar of kerosene
they didn't have to buy, they probably spent upwards of $1000 on exotic
aerospace hardware. Finally, they gave up and just bought kerosene-based
engines from the Russians.

So then there's Elon Musk. And of course there's a ton of brilliant rocket
science in the Falcon, but much of the reason for SpaceX's success is because
it doesn't optimise _solely_ on the rocket science. They optimise for cost as
a whole, and consider factors like design, manufacturing, operations,
reusability, etc. to be relevant to the question of cost.

For example: the Falcon 9 would undoubtedly be more efficient if it had a
hydrogen-based upper stage. But doing that would cause it to lose most of its
commonality with the lower stage, requiring an entirely new design,
manufacturing, and operations workforce. Which would cost several orders of
magnitude more than the extra kerosene required to fly a "sub-optimal" rocket.
The reason they've already cut the price of launch by about 80% vs. (say) the
Space Shuttle is because they optimised the _whole system_ , keeping the
unique part count and operational complexity as low as possible.

I still sometimes hear old-school rocket scientists grumble about how the
Falcon is a less optimised vehicle than the Shuttle, though. They just don't
get it. Never will.

Anyhow, that was a tangent. Fascinating to think that wind turbines might be
amenable to a similar class of disruption.

~~~
masklinn
> Anyhow, that was a tangent

It's also untrue, US rocketry kept varied propulsion types throughout its
history including both RP1-only and LH2-only as well as mixed stages, HTPB and
Aerozine. Your painting of rocket scientists as some sort of confederacy of
dunce unable to get a grip on tradeoffs is not only inane it's insulting
bullshit.

~~~
HCIdivision17
I started reading _Ignition!_ and it is a _hoot_. I really get the impression
that the rocket fuel scientists fixated, not because of personal issues
(though hilarity ensues there), but because the search space is damn large (at
least while still discovering how fuels interacted). Or worse, it just takes a
damn long time to even properly test. So when you found something promising,
you really dug into it.

~~~
nkurz
Yes, it's a fantastic book. Not necessarily a good role model for future work,
but it perfectly captures the spirit of rocket science at the time:
[http://library.sciencemadness.org/library/books/ignition.pdf](http://library.sciencemadness.org/library/books/ignition.pdf)

Everyone who grew up idolizing rocket scientists should read it. If you have
problems with missing pages or broken figures, try a different PDF viewer. The
PDF has something odd about it that confuses some in-browser viewers.

------
neilk
Erm, I don't know if I trust Cringely when it comes to this sort of thing. He
sold a reality show to PBS, "Plane Crazy (1998)"[1] with the promise he could
design and build a small plane in 30 days that was unlike any other that had
ever been built.[2]

His engineer just flat out refused to produce any plans for this design. He
tried to make something like his plane happen anyway, going without sleep for
weeks, and had a meltdown on camera. The show eventually had to be about him
giving up on his cherished design and building a throwback to biplanes, with a
family of artisans who are experienced in building them.

I had the feeling that Cringely was trying to channel Steve Jobs and it didn't
work out. (Note: Jobs drives _other_ people to do impossible missions without
sleep, not himself, and doesn't display his work until it's ready, giving the
appearance of effortless superiority).

Anyway as for this wind farm idea, the evidence of his friend's alternative
propeller design is interesting. But let's also note that that this friend
chose not to pursue wind farms, maybe for a reason.

[1]
[http://www.pbs.org/cringely/pulpit/1998/pulpit_19980724_0005...](http://www.pbs.org/cringely/pulpit/1998/pulpit_19980724_000578.html)

[2] EDIT: I am not an aviation person, and my memory of this is poor, but from
Googling I see apparently he wanted to make it out of unusual materials, have
foldable wings, and put the engine behind the pilot. I have a memory of his
design requiring the pilot to straddle the drive train to a front-mounted
propeller. I don't know how problematic that is, but I remember it as being
presented as a major problem.

EDIT 2: To be honest I feel a bit bad now about this being a top-voted
comment, as Cringely learned a lesson on camera that many startup people learn
behind closed doors – confidence is great, but trying to innovate in too many
directions at once will kill you. Maybe that means that he is more cautious
now, so perhaps he's _really_ sure this thing will work. On the other hand, it
was the first thing I thought of, that maybe he doesn't have a great track
record with aviation iconoclasm.

~~~
rhaps0dy
> His engineer just flat out refused to produce any plans for this design Do
> you know why? I'm thinking maybe it's because it was dangerous for the
> pilot?

~~~
neilk
Sorry, I'm relying on my memory of a show I saw like 20 years ago. I know
nothing special about aviation. But I just found a contemporary thread about
it here from other homebuilt aviation enthusiasts.

[https://groups.google.com/forum/#!topic/rec.aviation.homebui...](https://groups.google.com/forum/#!topic/rec.aviation.homebuilt/0uMOHlci8DQ)

------
Houshalter
Slightly relevant, here's a really weird wind turbine designed by a computer:
[http://m.youtube.com/watch?v=YZUNRmwoijw](http://m.youtube.com/watch?v=YZUNRmwoijw)

~~~
NicoJuicy
The note on the video is quite funny:

Note: I have since discovered I used the wrong viscosity for air on this
experiment, so the results aren't valid for use on the earth. (Maybe Jupiter.)

~~~
Houshalter
Ah, well. It's still interesting. The design of the turbine is really crazy
and not what I would have expected in any environment. So I suspect if he
corrected the parameters, it would still come up with a crazy and clever
design for Earth use, that humans wouldn't think of.

------
lorenzfx
I'm not saying he is wrong, but he makes some bold claims without giving any
proof.

Some examples:

> Twelve blades is a nice number.

Why twelve? Why not 50, it's a nice number as well.

> Lipps turbines can operate in faster winds [...] turbines could be allowed
> to run 24/7 in any wind with no computer

So even in the strongest winds turbines with 40 feet blades do not need to be
stopped?

> using permanent magnet generators instead of alternators, but those are more
> expensive > Use permanent magnet generators leading to [...] even lower
> cost.

Which is it now?

> what matters isn’t power efficiency per turbine so much as power production
> per acre of wind farm.

Isn't it rather electricity production efficiency in terms of invested
capital?

~~~
amelius
I get the feeling that the best answer to the question is that empirical
testing (perhaps by simulation) points out that three is the optimal number of
blades.

This leads me to the question: is it possible to determine a good rotor design
by using optimization techniques such as simulated annealing or genetic
programming? Or are the simulations too costly?

~~~
Bartweiss
I can help with this a bit.

The simulations are quite difficult - flow simulation is well-established, but
it's a big step from that wind farms. You need to simulate many turbines
interacting at a specific site, under a variety of conditions. That's not the
problem with modeling single turbines, though.

Rotor design is hard to simulate productively for the same reason that
Cringely's analysis is flawed: many of the biggest factors are unrelated to
everyday running.

\- Even blade counts create resonance patterns that stress your tower.

\- High solidity designs suffer more stress in storms (even while stopped), so
they break more

\- Noise interferes with putting rotors near houses or over pastures

\- Storage is difficult and consistency is valuable, so expanding the
operating range up to high winds is less useful than expanding it down to low
winds

And so on. If you model pure efficiency, the sims are pretty easy. If you
model real value, you either can't do it, or you get a search space so jagged
that finding maxima is hopeless.

------
Jedd
Looks like a fine opportunity to ask - whatever happened to vertical axis wind
turbines?

They sounded like they had a bunch of advantages, not least a much higher
tolerance for extreme wind conditions, less stress on long (suspended) blades,
possibly less gearing issues in translating motion back to the ground - but
presumably they had / still have distinct disadvantages?

~~~
knodi123
Even sexier (and less field-tested) than vertical turbines are windbelts.

[https://en.wikipedia.org/wiki/Windbelt](https://en.wikipedia.org/wiki/Windbelt)

> Prototypes of the device are claimed to be 10 - 30 times more efficient than
> small wind turbines. One prototype has powered two LEDs, a radio, and a
> clock (separately) using wind generated from a household fan. The cost of
> the materials was well under US$10. $2–$5 for 40 mW is a cost of $50–$125
> per watt.

------
dzdt
We all love the story about the clever little guy who thinks outside of the
box taking down the big giant corporation who does things the way they have
always been done. Cringely trys to tell this as such a story, or could be, or
could have been. But there is really no evidence backing it, just his desire
to tell a good story.

------
nabla9
One graph is worth thousand words.

Rotor power coefficient vs. tip-speed ratio.

[http://i.imgur.com/PONHerZ.jpg](http://i.imgur.com/PONHerZ.jpg)

~~~
55acdda48ab5
You have a computer with servos and winches fly parafoil kites to generate
power from wind. This is definitely the theoretically optimal answer. It's
also very low capital intensity.

[https://www.youtube.com/watch?v=j-qUaO-
xzrY](https://www.youtube.com/watch?v=j-qUaO-xzrY)

~~~
jessaustin
Lots of omitted details there. A kite can pull its tether from one location to
another location of lower potential energy, but how does it get back to the
higher-energy location? If we're talking about a circular train on a circular
track, half of the kites must continually have either a lower-drag
configuration or a lower-wind altitude. That's plausible, but that's a lot of
additional mechanisms, plus a lot of "cancelled-out" wind traction, plus a lot
of friction as the train rolls around the track. Will there be power left over
for electricity generation? Probably, but it isn't clear that it will be worth
all the trouble. If a reasonable prototype exists, it should have been in the
video.

------
Animats
In the 1970s and 1980s there was much more variety in wind turbine design.
There were two bladed machines, multi-blade ducted turbines, Darrieus rotors,
and other exotic technologies. Outputs were in the 50KW range. Pacheco Pass in
Northern California had examples of most of those. Some didn't work too well.
Loss of blade accidents were common in the early days, with blades thrown
considerable distances.

The three-bladed machines won out commercially. Machine size went up because
output vs cost decreases with size, at least up to 1-2 MW. Lots of little
machines were a pain to install and maintain.

Wind generators used to be AC generators synchronous to the grid. But with
higher power semiconductors available, putting a big AC-DC-AC converter on the
output to sync it to the grid is becoming popular.[1][2] This allows
generating some power during low-wind conditions, and provides much more
adaptability to wind gusts. When the wind speed changes, the blade pitch is
adjusted to compensate, but on big turbines, this takes tens of seconds. Being
able to adjust electrically in milliseconds avoids power grid transients.

The push for permanent magnet motors in wind turbines is more about converting
to direct drive and getting rid of the gearbox. Wind turbine gearboxes are a
huge pain, wearing badly for reasons that were only understood in the last few
years.

[1] [http://www.theswitch.com/wind-power/](http://www.theswitch.com/wind-
power/) [2] [http://new.abb.com/motors-
generators/generators/generators-f...](http://new.abb.com/motors-
generators/generators/generators-for-wind-turbines/doubly-fed-generators)

~~~
Ericson2314
Pacheco Pass or Altamont Pass?

~~~
Animats
Right, Altamont Pass. The Veg-E-Matic for birds - a long, narrow valley filled
with row after row of medium-sized wind turbines.

~~~
Ericson2314
Indeed it is.

------
vanderZwan
Relevant Low-Tech Magazine entries on wind-power, and small windmills:

 _Urban windmills harm the environment_ [0]

> A small windmill on your roof or in the garden is an attractive idea.
> Unfortunately, micro wind turbines deliver hardly enough energy to power a
> light bulb. Their financial payback time is much longer than their life
> expectancy and in urban areas they will not even deliver as much energy as
> was needed to produce them. Sad, but true.

 _Small windmills put to the test_ [1]

> A real-world test performed by the Dutch province of Zeeland (a very windy
> place) confirms our earlier analysis that small windmills are a
> fundamentally flawed technology

(Note that the picture shows that almost all windmills tested had three
blades)

 _Wind powered factories: history (and future) of industrial windmills_ [2]

> In the 1930s and 1940s, decades after steam engines had made wind power
> obsolete, Dutch researchers obstinately kept improving the – already very
> sophisticated – traditional windmill. The results were spectacular, and
> there is no doubt that today an army of ecogeeks could improve them even
> further. Would it make sense to revive the industrial windmill and again
> convert kinetic energy directly into mechanical energy?

Unlike this story, which certainly sounds interesting but shares no real data
to back it up, Kris de Decker thoroughly digs through sources to write
articles backed up by available data as best as possible.

[0] [http://www.lowtechmagazine.com/2008/09/urban-
windmills.html](http://www.lowtechmagazine.com/2008/09/urban-windmills.html)

[1] [http://www.lowtechmagazine.com/2009/04/small-windmills-
test-...](http://www.lowtechmagazine.com/2009/04/small-windmills-test-
results.html)

[2] [http://www.lowtechmagazine.com/2009/10/history-of-
industrial...](http://www.lowtechmagazine.com/2009/10/history-of-industrial-
windmills.html)

------
_Codemonkeyism
As a kid I always found it interesting that (some?) Spitfire had 4 blade
propellors and the main adversary, the [Edit] Bf109 had 3 [1] and wondered,
shouldn't there be an optimum?

[1] Not sure both changed the number of blades during WWII.

~~~
rusanu
You mean Bf109 I think. The P-51 started 3 and then moved to 4. Ditto P-47.
FW-190 and F6F stayed at 3 whole time afaik. Tempest started with 4. So it
varied. But there is a trend of the early (1939) designs to have 3 and the
late (1944) designs to have 4. I guess available power from the engine plays a
big role, as engines got more powerful they started fitting 4 blades. Using
the extra power on 3 blades would require longer blades (which is
problematic), spinning them faster (again, problematic as tips reach sound
barrier) or increasing the pitch (I guess there are aerodynamic limits for
that).

~~~
6stringmerc
This is a really cool write-up. Another thing that might be of interest was
the performance of the aircraft. There's a guy in Texas with 6 non-flying
109s, a couple P-51s, and some other stuff for sale as a lot. He's a former
stunt pilot, flew in the movie 'Battle of Britain' and several others.

In his words, the 109 handled much better at the limit than the P-51. The P-51
could dive and go very fast, but with poor control. In his opinion the 109 was
the superior aircraft.

Not sure if it relates at all to the prop discussion, but maybe in the grand
scheme of engineering? Those warbirds are fascinating pieces of hardware to
me.

------
tantalor
You mean like one of these?

[http://www.windpowerninja.com/wp-
content/uploads/2009/02/old...](http://www.windpowerninja.com/wp-
content/uploads/2009/02/old_wind_turbines.jpg)

------
justinph
Small turbines do exist. One was installed on This Old House recently:
[http://www.thisoldhouse.com/toh/tv/ask-
toh/video/0,,20961006...](http://www.thisoldhouse.com/toh/tv/ask-
toh/video/0,,20961006,00.html) (jump to about 15:00)

But, it does have three blades.

------
Aelinsaar
I like the idea of wind turbines, but in practice I think PV is the way to go
(long term). I realize that for now it's a blend of technologies, but PV
doesn't kill millions of birds and bats. I grant you, it's better than burning
coal, but still we can do better eventually.

~~~
Houshalter
House cats kill 1,000 times more birds than wind turbines. Even cell towers
kill more. It's nonissue.

~~~
mikeash
They won't kill the same kind of birds, though. For example, there's a new
rule raising the number of bald eagles which can be killed by wind turbines to
4,200 per year. I'm guessing that house cats kill few bald eagles.

It may still be a nonissue, of course, but the comparison with cats doesn't
tell the whole story.

~~~
Houshalter
Fair point, I was just responding to the idea that wind turbines would kill
all the birds, which isn't realistic. As a percentage of the bird population,
it's negligible.

I don't see any reason why bald eagles would be more likely to be killed by
turbines than other species of birds. If only 0.01% of birds are killed by
turbines, then they would only kill 1 bald eagle a year out of thousands.

Regardless, this is more of a reason to invent solutions for repelling birds
from turbines. Maybe we could come up with noises or lights that repel them.
Or drones, or a water cannon robot. But I'm not certain it's even an issue.

~~~
mikeash
The current rule is something like 1,200/year. There are about 143,000 bald
eagles in the US. The 4,200 number is set at a level which they think the
species can sustain. I don't know why bald eagles would be more likely to be
killed by turbines, but apparently they are:

[http://www.fws.gov/midwest/wind/wildlifeimpacts/index.html](http://www.fws.gov/midwest/wind/wildlifeimpacts/index.html)

"Not all bird species are equally vulnerable to wind turbines. Eagles appear
to be particularly susceptible."

~~~
Aelinsaar
Not all birds fly the same way, in the same regions, at the same altitudes.
Balds eagles tend to soar and hunt in places we like to put wind turbines.
Small birds tend to move smaller distances, often in about 100m around a water
source.

------
scblock
There is a lot of bad information here, and it appears there are others in
these who are also better informed than the author. Let me just hit up a
couple of points that are fundamentally wrong, though.

\- "Conventional wisdom says wind farms should have their turbines placed in
such a way that they don’t interfere with each other, the fear being that
placing one turbine too closely in the shadow of another will reduce the
efficiency of the showed turbine." True, and this is why we have wake models
based to predict the losses from other turbines and optimize placement.

\- "The rule of thumb, then, is that turbines be placed no closer than seven
diameters apart. Keep that number in mind." Not true. You may find that a 7x7
array is relatively common in offshore applications, but a typical onshore
application is more likely to be between 2-4 diameters apart in a row, with
rows 7-13 diameters apart front to back.

\- "Oh, and turbines are placed seven diameters apart. That’s it, no CFD."
Wrong. But CFD is generally computationally complex, so we usually use models
with reduced fluid dynamics equations to make it possible to iterate quickly.
See previous comment about wake models.

\- "In some cases wind farm automation can cost as much as the turbines,
themselves." I'd like to see these magical cases. A typical 2 MW turbine costs
$2 million to purchase, and about $3-3.5 million total as part of an overall
project of 50 turbines. SCADA is a minor fraction of this, as is operations.

\- "Shorter blades are stronger than longer blades, so the Lipps turbines can
operate in faster winds." This is a non-issue. There are very few sites in the
world that require even the highest wind speed turbine designs; most of the
world is less windy, and the majority of sites benefit from using turbines
designed for lower winds.

\- "Use permanent magnet generators and the turbines could be allowed to run
24/7 in any wind with no computer control required at all, leading to more
production at even lower cost." Computer control of turbines is a non-issue,
and the cost is minimal relative to the raw materials cost of the machines.

\- "This is because they use alternators that consumer electrical power to
energize their windings so there is no point in turning-on the alternator
(energizing those windings) until there’s enough wind to generate a net
positive amount of electricity." This is only a little bit correct, and mostly
not. Wind turbines by design generally need to be connected to the grid to
run, but winding energization is not why they don't start generating until
there is enough wind. Turbines are generally on all the time, and typically
consume anywhere from 10 to 50 kW at idle. And I don't know why he's using the
term "alternators" to describe the turbine generators. The most common
generator type is a doubly-fed induction generator, but squirrel cage
induction generators, permanent magnet generators, and synchronous generators
are often used. Usually turbines are connected to the grid through power
converters which allow them to run at various speeds while remaining
electrically synchronized with the grid.

\- "Remember the diameters are smaller so instead of hundreds of turbines
we’re talking about thousands of turbines for the same wind farm. Imagine a
field of mature dandelions." This is actually a problem. When you can get 100
MW with a 50% capacity factor by building 50 machines in one township in
Nebraska, why would you want to build 1,000 machines instead? How is that less
complex?

\- "Try breaking into the industrial wind power business without at least $1
billion in capital. It can’t be done. The incumbent companies like it that
way, too." Manufacturing is capital intensive. News at 11.

\- "Lipps wind farms could be closer to cities and therefore have lower
transmission losses, further increasing power output." Wind farm placement is
about where the wind resource is. It's an economic decision.

\- "The result of all this not starting and then stopping is that throughout
the year an average workload of 23 percent is reached by inland wind farms, 28
percent for coastal farms and 43 for off-shore." I have to assume his "average
workload" here (a term I've never heard in the industry) is equivalent to
capacity factor, which is the ratio of actual energy produced to the maximum
possible. Most new projects in the windy areas of the US have predicted
capacity factors of greater than 40 percent. High wind losses are typically
very low, and online time is typically very high.

\- "China will build the heck out of those smaller blades." China is also
building the heck out of the larger blades. China has more wind capacity
installed than any other nation.

\- "And no insane cows, either. Cattle can’t be pastured under wind farms
because the motion of the turbine blades and especially their sound drives
cows crazy." Tell that to these cows
[https://www.flickr.com/photos/ashcreekphoto/7793429362](https://www.flickr.com/photos/ashcreekphoto/7793429362)
(did he even do an image search before posting that? I've built wind projects
on cattle ranches.)

Why does this post use such an old, crappy US wind map? Why not the newer DOE
wind maps available at
[http://apps2.eere.energy.gov/wind/windexchange/wind_maps.asp](http://apps2.eere.energy.gov/wind/windexchange/wind_maps.asp)

I'm sure I could go on, but this is just a fundamentally misinformed article.
It's trying to make an aerodynamic argument (which I am not qualified to
judge) using a mess of bad or incorrect information.

~~~
notdonspaulding
Came here to point out that I live next to a dairy farm smack dab in the
middle of about (100) 1.5MW turbines. Cows aren't particularly intelligent
animals to begin with, but they certainly don't suffer from fainting spells
just because they graze under a huge turbine.

Other (industrialish) things cows don't mind: \- Tractors \- Feed grinders \-
Silage conveyors \- Automatic Milkers \- Being lifted to a horizontal position
to have their hooves trimmed. \- Having their eggs artificially inseminated.

I was unsure about the credibility of Cringely on the topic of turbine blade
count right up until I read this statement. Then I was sure about his
credibility.

------
tantalor
The 2016 tag is not really necessary; this was published today.

------
toolslive
"why... very often the turbines aren’t turning at all?" Someone told me that
demand varies and it's easier to shut down a windmill than a nuclear reactor.

------
tlb
More blades and closer spacing between windmills optimizes power / land area.
But what matters is power / capital cost.

~~~
mark-r
He tried to touch on that - making the blades shorter but in greater quantity
will drive efficiencies of scale in manufacturing and shipping. And smaller
turbines lead to cheaper towers. Hard to know if he's right without crunching
actual numbers though.

------
_Codemonkeyism
I'm interested in the results when Cringely builds his farm. For example
support costs from thousands instead of hundreds of turbines. How many on one
pole are best. Also building costs over time e.g. when costs go down due to
robots planting poles etc. which favors farms with more poles above those with
fewer poles.

------
yason
I don't know much about wind turbines and the behaviour of moving volumes of
air with regard to airfoils but there's one point I picked off of the article.

If I were to put my money either in the most advanced big-farm wind high-tech
or in something that is decentralized, mass-produced, and well-abused by all
kinds of groups of people, it would be the latter.

The article mentions that one billion is not enough to enter the game. That
surely excludes a lot of the smartest and brightest people who might come up
with new innovations and the billion-scale investments also seek conservative
returns, further culling new ideas.

------
stcredzero
This comment on the post is pure gold!

 _Fascinating! It’s not about asking questions, it’s about asking the right
questions! The first framing question is efficiency from blade to outlet, but
it’s really about effciency from capital markets to factory floor to farm to
outlet._

That should become a mantra. It's about efficiency from capital markets to
revenue per customer.

------
elcapitan
I would have guessed that it's a trade-off between efficiency and mimizing
public outrage in densely populated areas (yes, outside the US that can be an
issue). Three blades, when the turbine is not working, block less from the
view than a large number of blades (which converge towards giant white
surfaces).

------
at-fates-hands
Here's a much better Wind Resource Map than the one in the article:
[http://www.tindallcorp.com/site/user/images/USA_Wind_Map_for...](http://www.tindallcorp.com/site/user/images/USA_Wind_Map_for_Tindall_Transp_2.jpg)

~~~
scblock
[http://apps2.eere.energy.gov/wind/windexchange/wind_maps.asp](http://apps2.eere.energy.gov/wind/windexchange/wind_maps.asp)
has this map plus state by state maps available for download as relatively
high resolution PDFs.

------
coldcode
The more worrying part of this is that you need 1H capital to even try to get
into this business if all you do is build the monsters. So that means few
competitors (or even one) which makes monopolist behavior and unimaginative
thinking likely.

------
manmal
It seems Steve Jobs was inspired by Socrates:
[https://en.m.wikipedia.org/wiki/Socratic_method](https://en.m.wikipedia.org/wiki/Socratic_method)

------
xutopia
In some parts of the world they use 2 blades so they can lay down the system
when the wind is too high (think tornado/hurricane season)

------
trhway
The less number of blades - the higher efficiency, should be an odd number to
avoid standing wave and symmetric too. Thus 3.

------
mrfusion
Why can't the blades be staggered so they don't follow in each other's wake?

------
eonw
this is one of the best articles i have read recently. I too am a big fan of
always asking why and trying to buck the trend of "thats just the way it is".

