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Your BS detector should be bleeping at full force. There is a long, long history of failed attempts to build ducted wind turbines. The fundamental question is whether, for the revenue you'll gain from the energy gains, it's more efficient to put the money into building a duct or extending your turbine blades a bit more. Unfortunately, building all the extra structure to support the duct is expensive.

The history is long and discouraging. Paul Gipe has some good photos of recent attempts: http://www.wind-works.org/cms/index.php?id=541

    > "collected wind is channeled to pick up speed" doesn't
    > seem to be explained anywhere -- how exactly is that
    > done, and how much speed would the wind gain?

I'm not saying that your bullshit detector isn't justified, but that is a fairly self-explanatory claim (well, the "how" part anyway, numbers are lacking).

When you have an input flow, and the cross-sectional area is decreased, the speed has to pick up to compensate.

For example, if you have a fluid flowing through a 2ft-radius tube at 10 cubic feet/second, just divide the volumetric flow rate by the area to get a velocity of 5/(2π) ft/s. If later in the tube, the radius decreases to 1ft, that reduces the cross-sectional area by a factor of 4. But, 10 ft³/s is still being pushed in, so that's what needs to come out. That comes out to 10/π ft/s.

I'm sure there are losses when the fluid is compressible, but wasn't a sentence that tipped off my BS detector.

Coldarchon: Your posts are coming up dead- looks like you've been hellbanned since this post 773 days ago: https://news.ycombinator.com/item?id=3145705

Wow that's kind of sad. This guy has been continually commenting for over 2 years with no idea that he's been hellbanned?

I have show dead comments on and viewed his history. It's so sad - he comments every few days and oftentimes multiple times per day. He was never given chance to redeem himself to the community. That stinks.

Nice explanation! An example comes to mind is sticking your thumb over the end of a hose.

Ah, correct. As I mentioned, I'm only acquainted with fluid mechanics from a course I took a long time ago in uni.

To be fair, this is basic physics though, I'll go cry myself to sleep.

"I don't know enough about mechanics to make a proper assessment of this, but my bullshit detector is bleeping, though shyly."

Mine too…

One of the fundamental problems regular wind turbines need to deal with is the "V cubed" term in the power contained in moving air. For exactly the same reason that you need eight times as much power to make a car go twice as fast – if you build a turbine that can produce it's "nominal power" output in, say, 10m/s (~22mph) of wind, it'll need to be able to somehow deal with the turbine operating at 8 times nominal at 20m/s (45mph, a not unreasonable occasional windspeed in many places) and 27 times nominal power at 30m/s (a high, but certainly not yet "beyond reasonable safety design limits" speed).

My problem is with the numner on their Field Data page - they say they get an average "speed Ratio" of 1.8, and their turbine is rated at "600W at 12.5m/s". Ballpark extrapolation follows. I'll assume that's 12.5m/s at the turbine, or 12.5/1.8 = ~7m/s wind speed. About 15mph. At half that windspeed, there's 8 times less energy available, so 7.5mph of breeze will generate 75W, halve it again and output at 4mph drops down under 10W, and 2mph means low single digit Watts of output.

Now think about what happens to their turbine in a stiff breeze of 30mph? Where does the 4.8kW go? and when the once-in-5-years 60mph storm comes through, somewhere the best part of 40kW needs to be dealt with. Who engineers things with almost two orders of magnitude margins of safety?

It doesn't smell right to me.

Coudldn't you just close the tube? I assume they already use some kind of a one-way valve so the wind on the other side wouldn't suck and lower the preasure in the tube, you could just close this valve if the wind is too high, or even just open it a bit so you could still generate electricity?

Or better still, provide some kind of variable restriction such that the air flow through the turbine is right at it's max operating power.

Furthermore this tower isn't a lossless device, as the wind speed picks up I would guess that it gets "draggier" and less efficient at channeling and accelerating the wind.

But even if that's not the case making a variable restriction that could moderate the tunnel wind speed is a very easy problem to solve. Some kind of a damper and a control system that measures wind speed and adjusts the damper accordingly. You might even be able to use the turbine to do the measuring if you're clever.

This is where the 4.8kW will go if they haven't thought of the possibility of high winds.

http://www.youtube.com/watch?v=_e9uRSVun30

This seems precisely like an argument for a smaller turbine-based design INSTEAD of huge and (relatively) heavy blades. Turbines for car turbochargers and airplane engines can regularly (if I remember correctly) operate in the regime of ~100k RPM.

And like other commenters say: I think it would be much easier to restrict flow in the "funnel" part and most things I can imagine for a freestanding wind machine.

Looks like the blades are designed to crumple when they fail.

> Now think about what happens to their turbine in a stiff breeze of 30mph?

If the wind that goes into the turbine goes faster than a certain threshold, let some/most/all of the wind flow past the turbine. Maybe there is even a way to have the wind itself do that mechanically, similar to a pressure valve.

Don't you need 4x the energy to make a car go 2x the velocity? The drag equation is force-drag = 1/2 p v^2 c a [1]. Or is there more at work here?

1: http://en.m.wikipedia.org/wiki/Drag_equation

Right, drag scales with the square, but you're also going into that drag at a higher velocity, so power scales with the cube.

Or to break it out at more length, work is force times distance, right, and power is work over time. If it takes X amount of work to cover a distance at a given speed, it takes 4X to do it in half the time, since, as you point out, the drag (force) scales with the square of velocity. But you also accomplished that work in half the time, so the power required is 8 times the original. Make sense?

Ahh, thank you very much! Makes sense. I was conflating work and power...

There might still be something interesting in this design compared to the conventionnal wind turbines, if you imagine several output tubes and control the closing/opening of those tubes according to windspeed you'll be able to modulate the nominal power you mentionned.

You just need a "wastegate" similar to what is found on an automobile turbocharger. If too much air is moving into the generator turbine, you open some vents to bypass it.

My biggest problem with it is that no one outside of SheerWind has been allowed to test the system.

It kind of sounds like what happens with Andrea Rossis Energy Catalyzer[1], he was able to get milions in fundings over the years but never allowed to test it objectively claiming the reason is that he sold his patents or something. Several years later you can still not buy a cold fusion reactor.

[1] https://en.wikipedia.org/wiki/Energy_Catalyzer

I agree 100%. You can't just say "X% better" without defining the specifics of the environment in which you're operating. If they're claiming X% better in all environments, they're absolutely, 100% full of shit and they either need to stop outright lying, or do more work to validate their mistaken claims.

I'm not an ME or an expert in fluid mechanics, but I'm still curious.

I wonder how the efficiency of this compares to maximum power point tracking coupled with variable pitch turbines (minimizes airspeed required to start, but adapts both mechanical and electrical parameters in order to have peak power transfer at every windspeed)?

I wonder how the boundary layer introduced by the duct impacts efficiency. I understand there is a relationship between air velocity and efficiency, and I assume that it's easier to make high velocity systems more efficient, but in a ducted system such as this you're trading some of your total energy for a bigger pressure differential, and therefore speed. Is the amount of energy you're trading made up for by the gain in efficiency on the low-speed end of the curve? I imagine that on the high-speed (ambient wind, not flow over the turbine) end of the curve there's a drop in efficiency. It would be nice to see this quantified.

Innovative approaches to alternative energy are always nice, but I see a few issues (that may have engineering solutions):

1. In order to drive generator there needs to be a lot of wind. According to Do The Math only small portion of US has favorable conditions for wind: http://physics.ucsd.edu/do-the-math/2011/12/wind-fights-sola...

2. This actually moves air, which robs a portion of kinetic potential even before it get's to generator. There are probably few more caveats with this that I am not seeing.

3. What happens with used wind? It just get shot out of the bottom? At what velocity, website speaks nothing about safe utilization of "accelerated" wind. So if we get 30-40mph wind, what happens at the bottom?

4. What will happen when it rains? This thing will channel water flying sideways just as well as air. So not only turbines need to be waterproof, but now imagine point 3 with heavy rain.

5. Wind turbines safely stop when wind velocity gets too fast. This will be harder with this construction because wind is accelerated. If wind turbine stops and they do not close some kind of shutter - see point 3.

Note: to be fair, part of the issue could be fixed pretty easily by directing exhaust back up. This however still presents problems with water and robs yet more power of winds kinetic potential.

Yes, at first I thought that the x6 improvement was over real scale turbine or at least a turbine of comparable bulkiness. In France more and more people put wind turbines on their roofs, even if the kwh production is far less than promised by manufacturers (gaps between forecast production and real production of +6000 %, yes that's 60 x are common). The authorities are even giving subsidies for the installation of those inefficient turbines. This might prove better for small scale installations.