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Exactly this. Wind power seems to be an area where the usefulness inversely correlates with spreading of a piece of news. 3 times the power of a conventional

Exactly this. Wind power seems to be an area where the usefulness inversely correlates with spreading of a piece of news. 3 times the power of a conventional turbine? Albert Betz would like to have a word with these Japanese inventors. http://en.wikipedia.org/wiki/Betz_law http://en.wikipedia.org/wiki/Betz_law If anybody's interested in improving wind turbines, they should look at what is costly in current turbines. It's surprisingly the steel tower that's the most expensive part.

bartonfink 15y ago
I think this is what you meant to quote. http://en.wikipedia.org/wiki/Betz%27_law http://en.wikipedia.org/wiki/Betz%27_law
mikeash 15y ago
Are current turbines already within a factor of 3 of Betz' law, or at least within a factor of 3 of a practical limit?
- D_Alex 15y ago
  Yes, they are within 20% of the Betz' limit. But you must understand that the Betz' law refers to "available power", and the "available power" is higher for a shrouded turbine due to its larger apparent diameter.
  - mikeash 15y ago
    Most informative, thank you.
D_Alex 15y ago
Shrouds do two things: 1) they improve the efficiency by reducing tip vortex losses; 2) they increase the effective diameter of the turbine, so Betz' law is circumvented to SOME degree. I worked for a time on shrouded propellers for ship propulsion and studied ducted propellers for aircraft. These are more efficient than unshrouded propellers - but in each case the difference is under 10% - this is combined gain from reduced losses and larger apparent diameter. With turbines, things are a bit more complex, because with a well designed duct you achieve an effective diameter actually larger than the duct itself, and capture the additional wind energy from that extra area. Taking things to absurdity, I am fairly sure (without doing the math...) that you could have a relatively small turbine inside an enormous duct, and achieve 3x the power of an unshrouded turbine of that diameter. But this is a poor solution, because the large duct will surely cost a lot more than a larger conventional wind turbine.

bartonfink 15y ago

I think this is what you meant to quote. http://en.wikipedia.org/wiki/Betz%27_law http://en.wikipedia.org/wiki/Betz%27_law

mikeash 15y ago

Are current turbines already within a factor of 3 of Betz' law, or at least within a factor of 3 of a practical limit?

D_Alex 15y ago
Yes, they are within 20% of the Betz' limit. But you must understand that the Betz' law refers to "available power", and the "available power" is higher for a shrouded turbine due to its larger apparent diameter.
- mikeash 15y ago
  Most informative, thank you.

D_Alex 15y ago

Shrouds do two things: 1) they improve the efficiency by reducing tip vortex losses; 2) they increase the effective diameter of the turbine, so Betz' law is circumvented to SOME degree. I worked for a time on shrouded propellers for ship propulsion and studied ducted propellers for aircraft. These are more efficient than unshrouded propellers - but in each case the difference is under 10% - this is combined gain from reduced losses and larger apparent diameter. With turbines, things are a bit more complex, because with a well designed duct you achieve an effective diameter actually larger than the duct itself, and capture the additional wind energy from that extra area. Taking things to absurdity, I am fairly sure (without doing the math...) that you could have a relatively small turbine inside an enormous duct, and achieve 3x the power of an unshrouded turbine of that diameter. But this is a poor solution, because the large duct will surely cost a lot more than a larger conventional wind turbine.