Saturday, August 12, 2017

Two-bladed offshore turbines

Photo from Seawind Ocean Technology
Wind turbines have become very common across landscapes all over the world, and they all have three blades. I have never thought about why there are three blades, but I would have assumed that it's because there is a technical advantage to that particular configuration. In a recent article I read, however, the CEO of Seawind Ocean Technology, a wind turbine system development company, argues that for offshore wind turbines, two blades would be more economical and efficient.

The article (June 2017) is an opinion piece on the website Recharge, which describes itself as "The global source for renewable energy news & intelligence." This website is a good source of material for engineers (and teachers of those engineers) who are working in renewable-energy industries. However, one must subscribe to the website to gain access to the articles. The author of the article, Martin Jakubowski, has fortunately also uploaded his article on LinkedIn, where I was able to access it.

The article, "Two-bladed offshore turbines could cut the cost of energy by 50%":
https://www.linkedin.com/pulse/two-bladed-offshore-turbines-could-cut-cost-energy-50-jakubowski

It would be interesting to start a discussion with students about why they think wind turbines have three blades. Jakubowski says that, "Three blades did not become the standard due to technical considerations or a systemic approach to the fundamentals of wind turbines, but because of the trial-and-error approach of the industry's 'garage' pioneers in 1970s Denmark. The three-blade configuration simply worked, so was used repeatedly."

He then goes on to explain why the two-bladed turbine is a better choice, particularly for offshore turbines. In this way, the article follows the conventions of an opinion essay, including many of the phrases used for presenting an argument, making a concession, and giving a rebuttal:
  • And perhaps more importantly ...
  • ..., but this shortfall is more than offset by ...
  • In fact, recent university studies have found that ...
  • It is also worth noting that ...
  • The only relevant disadvantages, ..., are unimportant offshore.
  • Studies show that ...
And a clear conclusion:
  • While developers, financiers and insurers might initially be more wary of two-bladed offshore machines, the potential for increased reliability and LCoE reduction will be hard to ignore. The future will have two blades, not three.

In making his arguments, he uses many comparisons and phrases of cause and effect. Again, these phrases are very useful for students to notice when either writing or presenting support for opinion.

Some examples (with my emphasis):
  • ...two-bladed rotors are better suited for wind turbines because of their flexible configuration - namely, their attachment to the shaft by a flexible hinge.
  • This allows the rotor to have a second degree of freedom: to both rotate (first degree) and to teeter around the axis of the hinge like a seesaw (second degree).
  • This flexible hinge reduces the impact of cyclic loading (fluctuating stresses and strains from the wind), and strongly reduces wear and tear - fatigue - on the components, thus extending the lifetime of the turbine
  • The elasticity of this teetering hinge also removes the need for the blade pitch mechanism - the number-one source of failure in wind turbines - which controls the angle of the blades. Power output can instead be closely controlled by simply yawing (turning) the turbine into or away from the wind.

These are only a few examples; most of the article is written in this way, and is therefore a great source of such material. Notice, also, how the writing focuses on audience by explaining or defining terms that might not be known outside this particular field, e.g., flexible configuration, cyclic loading, yawing.

There are also many collocations that are useful for writing or speaking about other type of technical advantages (with repetitions of produce, reduce, create:
  • produce energy from
  • created a market for
  • reduces the impact of
  • reduces wear and tear
  • extending the lifetime of
  • removes the need for
  • source of failure
  • controlled by
  • reduces the cost of
  • removes the need for
  • potential for increased reliability


Finally, there are many adverbs used in the article, which I particularly like to make my students aware of, since they tend not to use adverbs much in their writing (or confuse them grammatically with adjectives):
  • simply
  • repeatedly
  • likely
  • arguably
  • largely
  • namely
  • strongly
  • closely
  • substantially
  • importantly
  • dramatically
  • costly
  • virtually
  • relatively
  • slightly
  • initially

There are also many useful linking and transition words, including those common to stating arguments (rather than, due to, not ... but because of, yet, however, such as, namely, in fact), but I will leave that to readers to identify.


The only language aspect of the article that I wasn't happy with was the incorrect use of less instead of using fewer in the phrase with less parts. This, in fact, is the same kind of error my students make - using less for both count and noncount nouns. In this case, what would be the best course of action:
  1. change the error before giving the text to the students (good model)
  2. leave the text as it is (authentic source)
  3. tell students there is an error in the use of less/fewer and have them find it (raise awareness)
  4. other choice?

It would be interesting for readers of this blog to give their point of view in the comments - whether engineers, engineering students, or teachers of engineering students.

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