Wind turbines just seem to keep growing. Predictions a few years ago that a 120-metre diameter rotor was going to be the maximum, have turned out to be wrong, and 154-metre rotors are being installed now, with 180-metre ones being designed.

But a bigger rotor means longer blades; and more force being applied to a longer lever - the tower. At what point do the physical properties of the materials, or the changes in wind speeds at different heights off the ground, limit the maximum physical dimensions of a wind turbine?

  • They've got a way to go - as long as materials keep developing. Not too long from now they expect to get to the point where they could bridge the straits of Gibraltar with a single span bridge ("Intercontinental suspension bridge" :-) ) and about then a space elevator becomes viable although somewhat stronger materials would be nicer. And we can look forwards to Kin Stanley Robinson's Red/Green/Blue Mars synthetic diamond elevator cable. Wow!. How that translates into WT diameter I know not,but it's "bigger". – Russell McMahon Dec 22 '14 at 16:38
  • @RussellMcMahon thanks, that is extraordinary. I wonder if the differential wind speeds would be the limiter, then? Wind speeds vary considerably with height above ground, so the tip of the blade at the top would have very different forces on it to the tips of the blades at the bottom. – EnergyNumbers Dec 22 '14 at 18:26

With any given engineering field there is a learning curve. With wind turbines there is a big incentive to go big. The higher up you are, the more wind. In addition in many cases, it's easier to get permission to redevelop an existing wind farm with larger turbines than to get permission to build a new one.

Also higher air is less gusty, and taller masts get them out of hte way of low level birds.

The flip side is that as machines get bigger the strength of a beam increases with the square of the size, but the stress increases as the cube. You don't see elephants with the proportions of an antelope.

The differential wind speed isn't that big of an issue. I suspect they will change the pitch of the blade. This will also allow them to keep running in severe wind.

Some problems with very large horizontal axis turbines are beginning to become apparent...

  1. Component supply.

  2. Transportation of large components.

  3. Footings of large cantilevered towers.

  4. Problems with erecting large systems on land and in water.

  5. Gearbox problems.

  6. Maintenance, especially in the ocean.

For more information on each of those items see the first few pages of a presentation by Dr. Brian Kirke at:

http://www.cyberiad.net/library/pdf/ringdrivevawtsept09.pdf

Although the introduction of that report focusses on Australia, many of the same problems are relevant to in other regions. (The rest of the report looks at an innovation that is not really relevant to your questions).

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    That's from 2009, and since then not only has deployment of very large HAWTs increased, so has the size of them. So all of those turned out to be wrong at the time. – EnergyNumbers Jun 8 '15 at 19:26
  • Agreed - many problems are being addressed successfully. It's difficult to predict the impact of new materials and technology, so it's no surprise that some aspects of the report are inaccurate, in hindsight. The graph on page 7 of the report shows the increases in uptake of 5MW+ turbines in 2009 and 2010, and that it was increasing at the time. 10MW versions are now available. Those turbines do, however, require specialists to maintain the (super-conductor) generators and the advanced cooling systems. That's not an insurmountable obstacle, but it is hazardous, expensive work. – Lysistrata Jun 8 '15 at 21:47
  • Are you sure 10MW are available now? Which supplier does them? I thought the Vestas 8MW was the current largest commercial turbine. And I thought all the superconductor trials had stalled, so I'm very interested to see more news on this - do you have a link? – EnergyNumbers Jun 9 '15 at 6:21
  • I stand corrected. I misread a few articles that said two 10MW turbines (Sea Titan built by AMSC and another by Sway) were now in existence, e.g. power-technology.com/features/… I think Sway may now be bankrupt. 10MW turbines are being contemplated by several manufacturers, and some modelling studies can be found on the net, but the projected date for them being commercially available is about 2020. – Lysistrata Jun 9 '15 at 13:22

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