A Fishy Idea, But Stay Downwind

It is always nice when you come across a scientific result that is counter intuitive, and works better than expected. This latest one is all about wind farms. Dabiri from CalTech has published a nice paper on a new arrangement of turbines for wind farms in the J of Renewable and Sustainable Energy (1). In the BBC interview, the author said that the design uses the same fluid dynamics that is found in the movement of shoals of fish (2).

A conventional wind farm has large propeller blades which are built high up in the air to capture higher wind speeds and have to be spaced about 5 blade diameters apart so that the flow from one windmill doesn’t interfere with its neighbors. The result is acres of eyesores that can be seen for miles and miles yet only produce about 2 watts/square meter when there is a good breeze blowing. For the number crunchers among us, recall that it takes 5 billion watts to power New York City.

Now, there are other turbine designs out there. There is the vertical axis wind turbine which has a long skinny cylinder mounted on end with the blades going up the cylinder. The counter-intuitive development (to me at least) is that they are more efficient when crowded together in pairs which contra-rotate. The vortices work together to give more than twice as much power as two isolated ones. Even better, the ones downwind lose very little from the upwind disturbance.

The result is that a nicely packed vertical turbine system can produce 10 times as much output per square meter as the now old fashioned sort that we have all over the place. Even better is that they do this at a tenth of the height so that they are about 10 meters high instead of 100 meters.

 I can imagine that the local bird life could get confused if they fly into the array of windmills. The vortices will spin them around in a variety of directions and they will probably call that farm the ‘funny farm’ in bird language. The author points out that the design is also applicable to underwater turbines and perhaps the small fish will be able to cope better than the birds as the shoals are already used to going round and round in random circles.

  1. http://dabiri.caltech.edu/publications/Da_JRSE11.pdf
  2. http://www.bbc.co.uk/news/science-environment-14452133

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