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People have been working on shrouded wind turbines for decades. Over and over again, the shrouds end up costing more than the cost of extending the blades and t

People have been working on shrouded wind turbines for decades. Over and over again, the shrouds end up costing more than the cost of extending the blades and tower enough to capture the equivalent amount of wind. I won't say that it will never work, but the list of failures is so long that anyone who mentions shrouded wind turbines without mentioning their history of failure should be suspected of being clueless. Inventing a new name for them, like "wind lens," makes them even more suspect. For a weak census of recent attempts, see Google Image Search: http://www.google.com/search?q=ducted+wind+turbines http://www.google.com/search?q=ducted+wind+turbines 1868, Ernest Bollee in France: http://en.wikipedia.org/wiki/%C3%89olienne_Boll%C3%A9e http://en.wikipedia.org/wiki/%C3%89olienne_Boll%C3%A9e 1926, Dew Oliver, San Gorgonio Pass in California, USA: http://books.google.com/books?id=7M9C1Adp0yQC&pg=PA46&lpg=PA46&dq=dew+oliver+turbine http://books.google.com/books?id=7M9C1Adp0yQC&pg=PA46&#3... ("The abandoned [Oliver] turbine remained at the top of San Gorgonio Pass for almost two decades until it was dismembered for its scrap metal during World War II.") 2005, Enflo turbine, still trying in 2011: http://www.enflo-windtec.ch/ http://www.enflo-windtec.ch/ 2007, FloDesign: http://fdwt.com/ http://fdwt.com/ $56M in funding so far. 2008, Marquiss Wind Power: $1.3M Series A in 2008, now dead: http://www.marquisswindpower.com/ http://www.marquisswindpower.com/ To be fair, Enflo and FloDesign haven't failed yet, or at least their websites are still up.

Gravityloss 15y ago
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.
illumin8 15y ago
Please excuse me, I am not well educated on wind turbines, however, wouldn't it be beneficial, once you have extended the blades and tower as much as possible, to still use a shroud? After all, there is a finite amount of space between turbines and the ground, and you cannot make the towers infinitely tall. Please correct me if I am wrong, but it seems to me that as long as the shroud or "wind lens" costs less than the price of building a second tower, it would seem that a 2x or greater increase in power output would be preferable to building a second tower, once you have increased the blade and tower height to the maximum efficient length.
- Gravityloss 15y ago
  As much as possible would probably mean a 600 m high turbine with 300 m blades made of pure carbon fibre or something like that. That could cost hundreds of millions and would be a useless monument. Look, it's a simple cost trade - currently the most economical turbines are in the 1 to 3 megawatt range and roughly 100 m rotor diameter. Tower cost is probably exponentially related to height for example. so the things balance out at that point.
  - ScottBurson 15y ago
    Tower cost is probably exponentially related to height Exponentially? So that every additional 50 feet, say, doubles the cost? I seriously doubt it. I would expect a quadratic relationship: the incremental cost to make it taller is proportional to the current height. Maybe I'm missing something and the relationship is cubic, but it's certainly not exponential. (I know, maybe you didn't mean "exponentially" literally. But we're engineers here :-)
    - nosse 15y ago
      I'm confused with the math used here. I think exponential is something like you double the height, and quadruple the costs. And that doesn't sound unrealistic to me.
      - 15y ago
synnik 15y ago
I'm doing my own renewable energy startup right now, with our own innovations in turbine design. And while the engineering is critical, it is not the problem with the industry. Energy startups fail primarily due to a lack of appreciation for the intensive capital required to make renewable energy work. This is an industry where every project will cost millions of dollars, hundreds of millions, or even a billion for truly large-scale operations. And that is EVERY project. You do not just come up with a design, test it, then repeat it 500 times. Each site has its own unique properties, each turbine need to be manufactured and shipped, connected into a grid, operated and maintained. So you need a permanent source of massive amounts of cash to operate. Your standard VC firm normally is not an option because the ROI is likely to be 10 years out, and that is too long for most investors. When the ROI does come in, it is massive. But this is a high-risk, long-term play, and it just doesn't match the interest of most VCs. We have built our first production units, field tested them, and are ready to roll, but have spent the last 3 months lining up finances because we do not want to be another failed company added to the list.
- acangiano 15y ago
  This is an area where I think government should provide generous grants and investments. Innovation for this type of problem is possible, but it takes more than 2 guys in a basement. Plus, as you mentioned, few VCs will want to wait a decade to see the results. Government can wait, however. I'm not in the field, so I'll naively ask: Is the US government, or any government for that matter, doing anything about it?
  - jerf 15y ago
    Energy production is one of the purest of the wealth producers. If the energy producer can't break even on their own strength, then needing government subsidy (especially indefinitely) is all but a mathematical proof that the subsidized energy production method is a net loss to society as a whole; were it not, they would be profitable and not need the subsidy. See also corn-based ethanol. Yes, I am aware of subsidizing R&D but that has diminishing returns too, and given the amount already poured in around the world and the rather dismal returns, I'm underwhelmed by the proposition that pouring even more in will turn things around. You can always claim that if you just keep pouring the money in it'll all turn around; it's a null argument when it comes down to it. (We'd almost certainly be better off pouring equal funds into getting nuclear going instead.)

Gravityloss 15y ago

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.

illumin8 15y ago

Please excuse me, I am not well educated on wind turbines, however, wouldn't it be beneficial, once you have extended the blades and tower as much as possible, to still use a shroud? After all, there is a finite amount of space between turbines and the ground, and you cannot make the towers infinitely tall. Please correct me if I am wrong, but it seems to me that as long as the shroud or "wind lens" costs less than the price of building a second tower, it would seem that a 2x or greater increase in power output would be preferable to building a second tower, once you have increased the blade and tower height to the maximum efficient length.

Gravityloss 15y ago
As much as possible would probably mean a 600 m high turbine with 300 m blades made of pure carbon fibre or something like that. That could cost hundreds of millions and would be a useless monument. Look, it's a simple cost trade - currently the most economical turbines are in the 1 to 3 megawatt range and roughly 100 m rotor diameter. Tower cost is probably exponentially related to height for example. so the things balance out at that point.
- ScottBurson 15y ago
  Tower cost is probably exponentially related to height Exponentially? So that every additional 50 feet, say, doubles the cost? I seriously doubt it. I would expect a quadratic relationship: the incremental cost to make it taller is proportional to the current height. Maybe I'm missing something and the relationship is cubic, but it's certainly not exponential. (I know, maybe you didn't mean "exponentially" literally. But we're engineers here :-)
  - nosse 15y ago
    I'm confused with the math used here. I think exponential is something like you double the height, and quadruple the costs. And that doesn't sound unrealistic to me.
    - 15y ago

synnik 15y ago

I'm doing my own renewable energy startup right now, with our own innovations in turbine design. And while the engineering is critical, it is not the problem with the industry. Energy startups fail primarily due to a lack of appreciation for the intensive capital required to make renewable energy work. This is an industry where every project will cost millions of dollars, hundreds of millions, or even a billion for truly large-scale operations. And that is EVERY project. You do not just come up with a design, test it, then repeat it 500 times. Each site has its own unique properties, each turbine need to be manufactured and shipped, connected into a grid, operated and maintained. So you need a permanent source of massive amounts of cash to operate. Your standard VC firm normally is not an option because the ROI is likely to be 10 years out, and that is too long for most investors. When the ROI does come in, it is massive. But this is a high-risk, long-term play, and it just doesn't match the interest of most VCs. We have built our first production units, field tested them, and are ready to roll, but have spent the last 3 months lining up finances because we do not want to be another failed company added to the list.

acangiano 15y ago
This is an area where I think government should provide generous grants and investments. Innovation for this type of problem is possible, but it takes more than 2 guys in a basement. Plus, as you mentioned, few VCs will want to wait a decade to see the results. Government can wait, however. I'm not in the field, so I'll naively ask: Is the US government, or any government for that matter, doing anything about it?
- jerf 15y ago
  Energy production is one of the purest of the wealth producers. If the energy producer can't break even on their own strength, then needing government subsidy (especially indefinitely) is all but a mathematical proof that the subsidized energy production method is a net loss to society as a whole; were it not, they would be profitable and not need the subsidy. See also corn-based ethanol. Yes, I am aware of subsidizing R&D but that has diminishing returns too, and given the amount already poured in around the world and the rather dismal returns, I'm underwhelmed by the proposition that pouring even more in will turn things around. You can always claim that if you just keep pouring the money in it'll all turn around; it's a null argument when it comes down to it. (We'd almost certainly be better off pouring equal funds into getting nuclear going instead.)