01 September 2010

Windbelts

Windbelts

What a windbelt is

http://lh5.ggpht.com/_jtvOCEq74z4/TH6ykZ3JHbI/AAAAAAAAAF8/JP-zW8aBCAM/windbelt1.jpg

A windbelt is an alternative energy source invented by Shawn Frayne. It uses the principle of aeroelastic flutter. Basically it recovers power from a string that vibrates in the wind, like an Aeolian harp.

See also here

Promising

http://lh6.ggpht.com/_jtvOCEq74z4/TH6yhgvxcqI/AAAAAAAAAFs/bnFNGbwHlwE/Windbelt.jpg

  • They are cheap. That's undeniable. Less than $10 for the parts for a working model.
  • It works. He's selling them1 and they generate power. There are videos.
  • Less moving parts than a windmill. That's "less", not "fewer". It's got as many moving parts - more if there are multiple strings. But they don't move as much. You could hold your finger an inch away from the moving part and not get smacked by it.
  • Scalable? Apparently a 10 meter version is in the works.
  • Efficient? Shawn claims that a windbelt generates 10 to 30 times as much power as a microturbine under certain conditions; it makes 40 milliwatts in 10-mph breeze.

    That's promising, and it suits his plan of marketing it in the third world. But for more conventional use, I'm left with questions:

    • 10 mph is a low speed for conventional windmills. They get better at higher wind speeds. How does the efficiency compare at higher wind speeds?
    • At higher wind speeds, microturbines are not the most efficient means. One would want to at least compare against conventional windmills.
  • Noisy? Actually, no. According to Shawn's site, the windbelt is actually fairly quiet.

Could it be made a little more efficient?

Two ideas:

  • (Not by me. A commenter on Youtube suggested it first AFAIK)

    Put the generator at or near the center of the string, where it is exposed to more vibration.

    Or if it's difficult to give it a stiff platform there, at least put it somewhat away from the end, which is the part of a string that vibrates the least.

  • Generate power from the whole range of transverse modes. It appears to me from the demonstration that windbelt is only generating power from one transverse vibration mode. But a string has a whole family of transverse vibration modes, effectively doubling the opportunity for power generation.

    Addendum: I see that more advanced versions do essentially that: http://lh6.ggpht.com/_jtvOCEq74z4/TH6yj73M22I/AAAAAAAAAF4/bPvhnV3iVfo/humsix_triangle_27.gif

Where might it be used

Shawn basically talks about using it in third world countries that can't afford windmills. But I think one could aim higher than that.

In place of conventional windmills

http://lh3.ggpht.com/_jtvOCEq74z4/TH6yhNLYAsI/AAAAAAAAAFo/POocHP68TfA/ModernWindmill.jpg

Could they be used instead of conventional windmills? There are two reasons that make me think maybe:

  • NIMBY. After the Ted Kennedy / Narragansett Bay brouhaha, it looks like conventional windmills aren't politically easy (Don't ask me why, I thought they were scenic). Might windbelts be a little easier on the view?
  • Cross-section. A conventional windmill goes to heroic lengths to sweep its working surface over a large cross-section, but even so, a lot of the wind goes thru it without ever coming near the windmill's working surface. For a windbelt with (say) 2 meters between strings, the air is never more than 1 meter from the working surface.

On suspension bridges

In particular, vertically on suspension bridges. It's a great location:

  • The physical support is already there.
  • The electrical infrastructure is partly there - they are wired for road lighting and other electrical use.
  • There's a huge cross-section exposed to the wind.

http://lh6.ggpht.com/_jtvOCEq74z4/TH6yi6p88FI/AAAAAAAAAF0/VFuyZVUnWfA/clifton-suspension-bridge-bristol-gben440.jpg

On tall buildings

There is a lot of wind around tall buildings. They block the wind so it is all funnelled around them. It's actually a big problem, and can suck windows out and make it uncomfortable for pedestrians to walk nearby.

It's a problem many people have tried to solve, and tried to generate power from. But with conventional windmills, it's not easy. Where can you safely swing the blades? If you duct the wind to a turbine or similar, you waste a lot of power and it's noisy.

But a windbelt doesn't have that problem. And once again, having the physical and electrical support already in place is nice.

Footnotes:

1 Individually, not mass produced. See his FAQ.

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