Is there an aerodynamicist in the house?

Can any erudite JBer provide a laymans explanation of why wind turbines get bigger & bigger but never seem to have more than 3 blades? I am thinking of propeller blades which evolved from 2 to 3 to 4 to 5 (to 6?) blades as they transmitted increasing power through a diameter-limited disc. I also remember those farm wind pumps which resembled a turbofan with almost a "solid" disc of blades.

[In the good old days I would post on Tech Log but they have got so up themselves these days that they would probably not "accept" this question]

Thanks & apologies for the aviation inferences.

best simple answer here

Why is 3 the optimal number of blades on a wind turbine instead of say 5 or more? - Quora (http://www.quora.com/Why-is-3-the-optimal-number-of-blades-on-a-wind-turbine-instead-of-say-5-or-more)

The expert opinions on the above link, are very precise and professional.

Also if only two blades, they must be longer, thus the tower must be higher to gather the same "volume" of wind.

The point re two blades producing more stress on the hub is also valid.

The multi bladed old style wind mills were produced in a time when technology was rater basic, and mult blades were easy to produce, and mount, but also had much greater frictional loading.

glf

And ya get a closer shave.

http://www.waxing.net/wordpress/wp-content/uploads/men_shaving.jpg

Disclaimer: That's not me in the picture.


:{

And to think we all laughed at it in 1975...

SNL Transcripts: George Carlin: 10/11/75: Triple-Trac (http://snltranscripts.jt.org/75/75atriple.phtml)

Announcer: The Triple-Trac. Because you'll believe anything.

OK, but it's even weirder that moonlight isn't light enough for solar panels.

If you just stuck a label saying "Lunar Panels " on them, then they would work :ok:

Thanks for the helpful posts and links here, folks. I have learned something.

If you just stuck a label saying "Lunar Panels " on them, then they would work
someone needs to invent a panel with the "Solar-Lunar" switch :D.



.

Press Releases - Siemens Global Website (http://www.siemens.com/press/en/pressrelease/?press=/en/pressrelease/2012/energy/wind-power/ewp201207059.htm)

http://www.siemens.com/press/pool/de/pressebilder/2012/photonews/072dpi/PN201204/PN201204-06e_072dpi.jpg

It's all about torque....

No such thing as moonlight really,tiz just diverted sunlight.:)

Just for interest...when things go wrong. Apparently, owing to earlier damage, the operator of this turbine was unable to pitch the blade tips to slow/stop the turbine. The local authority had cordoned off the area.

turbine gone bad - YouTube (http://www.google.com/url?sa=t&source=web&cd=1&ved=0CEoQtwIwAA&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3Dti1ebjLephE&ei=1jgeUP3xKqO40QW69YDQCA&usg=AFQjCNFvfI1CdGMojRvRrDVt73XyhJyoRA)

Because 50 would be too many shades of fecking sunlight

Ozzy

[QUOTE]No such thing as moonlight really,tiz just diverted sunlight./QUOTE]
yep, and still not good enough! :sad:

turbine gone bad - YouTube

Warms the cockles of your heart.

Can any erudite JBer provide a laymans explanation of why wind turbines get bigger & bigger but never seem to have more than 3 blades?

not wishing to get too technical (because I don't have a clue).

Its to spin the generator just fast enough to get 60 cycle and still let the birds pass through

Wind Turbines - Siemens (http://www.energy.siemens.com/hq/en/power-generation/renewables/wind-power/wind-turbines/#content=Technology)

" Comply with all currently valid grid code requirements on relevant markets

Our proprietary NetConverter® power conversion system allows generator operation at variable speed, frequency and voltage while supplying power at constant frequency and voltage to the MV transformer.
The generator is connected to the MV transformer with NetConverter® power conversion system. This system provides maximum flexibility in the turbine response to voltage and frequency requirements, fault conditions, etc. and can be adapted to meet the requirements of relevant grid codes.
The power conversion system uses a number of modular water-cooled converter units in parallel mounting for easy maintenance."


;)

I have a friend who's an electrical engineer and works on gas-powered generation. The way he described it, when a generator of any sort is coupled to the AC grid directly, it always locks in to the grid frequency. This is why we can see rows of turbines turning in perfect sync with each other: they're on the AC grid. You have to adjust each "throttle" to make it generate the right amount of power, otherwise it will take power from the grid instead. In the case of wind generators, that "throttle" will be the blade pitch, of course.

That Siemens variable speed system is probably using rectifiers and inverters: variable AC -> DC -> Grid AC. There's at least one good reason to use DC in the system: it's much better for undersea transmission. AC in undersea cables can suffer major losses due to capacitance of sea water, which is not the case with DC. (The grid link between the UK and N. Ireland is a DC-DC link for that reason, even though the UK and Irish grids are both 50Hz and could be synced up without too much bother. )

If you rectify to DC at a offshore turbine, you just bus the DC outputs together, and no turbine will draw from the grid if the pitch isn't right. Carry the DC to land, attach to the inverter and feed on to the grid. Simple as. (Yeah, right!)

Yep, with the propriety VPower software in the converters Siemens machines can condition the grid [nationally if need be] for maximum efficiency even at idle.

Once you get into it, it's surprising just how "steam driven" the control and conditioning of the UK national grid has been for decades.

Things are changing dramatically.

dc tech.

Ultra HVDC Transmission System - Siemens (http://www.energy.siemens.com/hq/en/power-transmission/hvdc/hvdc-ultra/)

HVDC PLUS (VSC Technology) - Siemens (http://www.energy.siemens.com/hq/en/power-transmission/hvdc/hvdc-plus/)

gr.

Warms the cockles of your heart.


that it does.. more please !

A bit too much ambition juice :O

not necessarily blades any more:

http://images.gizmag.com/hero/venger-wind-oklahoma-medical-research-foundation-32.jpg

Is this the largest rooftop wind installation in the world? (http://www.gizmag.com/largest-rooftop-wind-farm/23733/?utm_source=Gizmag+Subscribers&utm_campaign=9ff10b4d67-UA-2235360-4&utm_medium=email)

Interestingly, Venger isn't merely claiming this as the largest rooftop installation in the US, but the largest building-integrated installation. As most building-integrated installations will be on the roof, this isn't a huge distinction, but it's a slightly larger subset of wind turbines all the same. Turbines can also be mounted on building facades. Inhabitat in its coverage calls this the largest rooftop installation in the world. We're happy to go along with that, unless anyone out there can point us to anything bigger still.

Sorry, Probes, but it looks like a set for a Terry Pratchett film (The Thief of Time).

Wind Turbines are being blamed for the loss of hundreds of expensive racing pigeons up here,the bastards!!
:= :rolleyes:

why me, Mads? :uhoh: It's not me who created them?? :)
Mr.D - isn't it too high for pigeons? Dunno anything about them, though.

The RAF tried to have the buggas banned up here as well so there must be summat in it.
:rolleyes:

They tried to hoover up all our seagulls, crows, pigeons and a solitary heron the other day - seven of their red vacuum cleaners came over our town centre at rooftop level. Miracle they didn't convert the shopping centre to a smoking crater.

Articles Template (http://www.countryguardian.net/Wind%20Rush%20Aviation.htm)

RAF Benson - News and Weather (http://www.raf.mod.uk/newsweather/index.cfm?storyid=5F808413-5056-A318-A82B672ED1B247F1)

AC in undersea cables can suffer major losses due to capacitance of sea water, which is not the case with DC. (The grid link between the UK and N. Ireland is a DC-DC link for that reason, even though the UK and Irish grids are both 50Hz and could be synced up without too much bother. )

If you rectify to DC at a offshore turbine, you just bus the DC outputs together, and no turbine will draw from the grid if the pitch isn't right. Carry the DC to land, attach to the inverter and feed on to the grid. Simple as. (Yeah, right!)

bnt,

I'm not sure capacitance of sea water is the issue! Rather, any ac cable operating at transmission voltages will suffer significant capacitive loss due to the dielectric needed to insulate it. This is why overhead lines are the preferred transmission method where practical; air is the insulator in that case!

In the case of the GB-NI link, (where incidentally, the cables are actually buried in the sea bed) 250kV DC is used. You mention that the grids could be synchronised...this is true, but not desirable. In the case of a transmission fault in NI, the DC link prevents the fault from impacting the GB grid. If the link was ac, and synchronised, any fault in NI would drag down voltage and frequency on the GB grid (and vice-versa). The DC link prevents this, as it effectively decouples the two ac grids.

With regard to wind turbines, early designs were induction generators; these could only generate when connected to a live source, and would output at the source voltage and frequency. If the turbine sped up (as wind increased), voltage and frequency would remain governed by the grid, but power output would rise. These turbines had no 'black start' capability. Newer machines can control their own voltage and frequency output, and this is now being used to allow large banks of turbines to assist with grid management, in the same way as conventional generating plant. This is achieved as you say with ac --> DC --> ac conversion.

Wind turbine technology is moving at an incredible pace. Ten years ago, it was only ever envisaged that turbines could compliment conventional fossil fuel generation; now, it is likely that wind will be the predominant generation source in some parts of the world. Here in NI, we have already seen more than 40% generation coming from wind on a given day. The old chestnut about what happens when there's no wind is now being set aside; there is always wind somewhere. It's just a matter of having an infrastructure that can move wind energy around in a stable manner.

The old chestnut about what happens when there's no wind is now being set aside; there is always wind somewhere.
and what about the Earth slowing down because of all the turbines? :E

The local authority had cordoned off the area.


No! Don't tell me ..... that was in Orkney, midsummer weather? Huh?

No? Really!

If the link was ac, and synchronised, any fault in NI would drag down voltage and frequency on the GB grid (and vice-versa). The DC link prevents this, as it effectively decouples the two ac grids.



This reminds me of an interesting "how to" in an ancient (~1910) electricians hand book:

===

To phase a generator to the grid a light bulb is connected between the generator and the grid. (This was well before osciloscopes etc)

The speed is first adjusted until the lightbulb intensity slowly varies, when the bulb is at a dark point have the apprentice throw the switch connecting the generator to the grid.

===

I loved the part about having the (expendable) apprentice throw the switch - remembering that back in those days large switch gear was all open - think giant knife switches and that major excitement could happen if the generator was not in phase with the grid.

Spectator: The great British wind scam (http://www.spectator.co.uk/features/8766481/the-great-british-wind-scam/)

The great British wind scam: the government responds (http://blogs.spectator.co.uk/coffeehouse/2012/11/how-the-government-prioritises-profit-over-helping-the-environment-with-wind-turbines/)

http://i6.photobucket.com/albums/y204/Badyin/Christmas%20Cards/greens.jpg

Like brave pilots flying under a bridge, Santa tried something new....

So that's a scam too.
I've wondered about the e-thing being 'greener' than paper - allegedly - (no need to print out everything etc) what are the actual costs? Considering electricity needed for the 'puters, server farms, cloud computing and supercomputing (and money needed for one's glasses and backpain-medication due to sedentary life). Versus pulp and paper. Which is actually more costly?