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  • one is the obvious one that it gets harder to manipulate the big items (blades, towers). Road transport puts absolute limitations on the size of what can be built onshore (around the 3MW limit); offshore can go further with factories directly on the seaside or near rivers;

  • another is that it is not so obvious that there is any economic gain in building bigger turbines. The economies of scale come from the size of the wind farm, compared to the cost of development, permitting, cable connexion and land use. On land, it made sense, with limited room available, to squeeze more MW in the same spot by using fewer turbines. If you have no land limitations, then you can put more turbines and intermediate sized ones might work just as well;

  • I'm not the best placed to comment on that (maybe Crazy Horse can) but I understand that the strains on the structures from really big turbines become massive, and hard to manage unless you seriously increase costs to reinforce the wind turbines / towers.

So we'll see. There's been talk of 5-10MW turbines offshore, but I've never heard any proposal to go beyond.

In the long run, we're all dead. John Maynard Keynes
by Jerome a Paris (etg@eurotrib.com) on Sat Dec 8th, 2007 at 03:13:36 AM EST
[ Parent ]
From Wiki:  For a given survivable wind speed, the mass of a turbine is approximately proportional to the cube of its blade-length. Wind power intercepted by the turbine is proportional to the square of its blade-length. The maximum blade-length of a turbine is limited by both the strength and stiffness of its material.

This means that after a certain point, mass is increasing relative to the added wind intercepted, limiting economies of scale.  New materials can change the equation, i.e. when carbon fiber is added to the load carrying blade spars.  Bard Engineering uses a very conventional turbine design for its offshore entry, where they simply scaled up standard 3-bladed geared turbines.  Their blades weigh ca. 28 t, the hub alone including the entire pitch system is around 70t, and the full nacelle including power train reaches 280t.

I don't have the REpower 5m weights in front of me right now, but I believe the blades, at approx. the same length, weigh 9000 k less, because they have extensive use of carbon fibre in the load-carrying members, particularly in the spar girders.  They will also be stiffer, meaning less glass as well.  Then correspondingly less steel is needed in the hub, and along key parts of the power train.

Multibrid saves similar weight in their blades by carbon fibre use, though they add some aloft weight by using one less gearbox stage but a correspondingly larger lower speed generator system.  Dinner (which i share cooking duties) calls.

Perhaps the blade, hub, nacelle, and total aloft weights are available on the net.  Comparing and contrasting these machines are perfect examples of the design tradeoffs the design team has to make.

And we haven't even begun to discuss the 2 new second versions of the Enercon 6MW turbines erected in Emden.

"Life shrinks or expands in proportion to one's courage." - Ana´s Nin

by Crazy Horse on Tue Dec 11th, 2007 at 12:58:27 PM EST
[ Parent ]
Crazy Horse:
From Wiki:  For a given survivable wind speed, the mass of a turbine is approximately proportional to the cube of its blade-length. Wind power intercepted by the turbine is proportional to the square of its blade-length. The maximum blade-length of a turbine is limited by both the strength and stiffness of its material.
Except that there's no reason why the thickness of a turbine blade needs to be proportional to the length.

Do you have examples of actual blade dimensions and materials for wind turbines of different nominal power?

We have met the enemy, and he is us — Pogo

by Migeru (migeru at eurotrib dot com) on Sat Dec 15th, 2007 at 03:42:51 PM EST
[ Parent ]

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