The Future of Wind Turbines: No Blades | Hacker News Reader

The Future of Wind Turbines: No Blades

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59 pointseurvin18 comments

OK, so: Betz's Law says that the maximum energy that any wind turbine can extract is 16/27 of the kinetic energy contained in the wind that it blocks. Modern three-blade wind turbines reach 75-80% of the theoretical maximum, across the entire area their rotors sweep out.[1]

That's why the classic windmill design is so classic: its efficiency scales with the square of the length of the rotors. The energy extracted by a windmill is (very roughly):

    wind_speed * 16/27 * 0.8 * π * rotor_length^2

But then the wind speed also increases with height.[2] So the game to design an efficient windmill is to sweep out as much cross-sectional area as possible, as high up in the air as possible, and that's how we get the iconic windmills we have.

I don't know anything about anything -- I just read this stuff on Wikipedia. But until a third-party engineer says otherwise, I'm super skeptical that a device like this with minimal high-altitude cross-section is anywhere in the game.

[1] http://en.wikipedia.org/wiki/Betz%27s_law [2] http://en.wikipedia.org/wiki/Wind_profile_power_law

> I just read this stuff on Wikipedia.

Same here. I've also read up on a lot of different designs, and have been paying attention for a while now.

There are a couple of points that have occurred to me about wind power. 1) Most supposedly exciting, new designs are minor variations on older designs with minor improvements in efficiency. 2) Some esoteric design are actually good for something, but not for massive wind farms. Think wind turbine as art in a public park, etc. 3) Media love esoteric designs and want to hype it as the next thing, even though they are nowhere near the efficiency of a big 3-blade on a tall pole design.

The article did say it's less efficient, but you can put twice as many in the same space which supposedly more than makes up for the power deficit. Plus no noise pollution or threat to birds and lower maintenance costs. Obviously a lot of technologies look good at this point, before they are widely deployed and tested, but I wouldn't count it out yet.

The efficiency loss can be overcome with better operational aspects: requiring less maintenance, being able to install anywhere, etc.

My first thought was "even if this is less efficient, the silence and lack-of-bird-killing means it would be viable to install places where NIMBYism etc. mean that traditional turbines can't be".

i.e. it may be sufficiently in the game to compete effectively against "no turbines" even if it can't compete against turbines directly.

It also seems like you'd be able to fit more of them into the same space. The company also claims that they're (allegedly) cheaper to manufacture and are (allegedly) cheaper to maintain. Even if the efficiency is less than those of a traditional windmill, it would still make sense to use them from a cost savings perspective alone.

That's if everything the company claims is true. Too many other alternative energy companies have made similar claims and failed to follow through for me to take this with anything other than a grain of salt.

edited for clarity.

Betz's Law applies to turbines, but it this thing really a turbine? "No moving parts" and the fact that it operates via oscillation rather than rotation implies that this is not in fact a turbine. If it is not a turbine then there is no reason to assume Betz's Law must apply to it, perhaps there is something else that governs efficiency in this case?

Betz's law arises from the fact that you can't very well stop air dead after you've extracted energy from it - it has to keep on moving to make space for new air. (Otherwise pressure would build up indefinitely, a clearly non-physical situation). So it applies to all such devices, rotors or no. (It doesn't apply to fluids because fluids don't compress, but that is a completely different story).

I am no means an expert, but from my understanding you are only partially correct. Betz's law essentially says that because the velocity of the fluid exiting the cross section of the turbine is lower than the velocity or the fluid entering, the exiting fluid must consume more volume, and that their is a calculable limit to that difference. If these devices are in fact using vortices/turbulent airflow to induce resonance then perhaps different rules apply to the amount of energy that can be extracted?

Substantial discussion of the concept and technology over here:

https://news.ycombinator.com/item?id=9523877

I followed the debate about renewables for quite some time and I heared stories like this before. A new design for wind energy with so obvious advantages. And you can read pretty similar stories for new solar or water power tech also pretty regularly.

I remember that already in the 90s I heared people saying that future wind turbines will have a funnel to focus the energy. Later kite-like flying turbines or turbines in donut-shaped balloons became a thing.

But wind turbines still basically look very similar than they used to be all the time, the biggest change is that they became much bigger. There's a reason for that: The design worked well and has been improved in details over the years. It's much easier to improve in small steps than to reinvent a completely new tech, which will have many downsides that the enthusiasts inventing them don't want to see.

That's not saying that it's entirely impossible that a completely new design of wind turbines will some day emerge. But I don't think it's very likely. And before I believe it I want to see them built at scale for a reasonable price. (Because one of the biggest advantages of the existing wind turbines - appart from them being environmentally friendly - is that their price dropped rapidly in the past years.)

Similar to the windbelt:

http://www.instructables.com/id/Windbelt-Redux--21st-Century...

Fluids tend to move as vortices so often reciprocating motion can be at least as efficient as rotary motion. For example it is (currently) difficult to replicate the efficiency of birds and fish with propellers.

Potentially (ahem) it's possible to extract work from ions in a flow, and if it's laminar there would be no vortex losses. Just for fun, here is an electrostatic turbine, which works a bit like an electrohydrodynamic (EHD) drive but in reverse. From what I understand, it's difficult to extract more work than it takes to ionize the fluid, so this cheats a bit by using liquid droplets:

http://www.wired.co.uk/news/archive/2013-04/3/bladeless-wind...

I personally like the idea of wind turbines being tethered high-altitude blimps.

I assume the high-altitude ones could be higher than birds fly.

They could even be used as in-flight recharge stations for drones.

The tethers wouldn't interfere with air travel?

Restrict airspace access for densely tethered wind-farms and if they are needed closer to cities then we can figure that out later.

I was thinking some sort of central tether connecting a large group of them then either directly beamed or daisy-chained balloons high up in the air. It would be an amazing technical and engineering accomplishment to do that but it might provide energy with minimal airspace disruption, though you wouldn't really want planes flying under them either, just in case.

Maintenance could involve having detachable cables (which would deploy a parachute and have bring lights in case a place was passing by at that time) so that the cable falls gently against the central tether and can be reattached using a heavy-lifting drone or blimp/drone hybrid.

It's amazing how high birds can fly http://en.wikipedia.org/wiki/List_of_birds_by_flight_heights

Unfortunately it's likely that many many types of animals take advantage of low-altitude wind-streams, especially during migrations.

But maybe we could place several of them into the jet-stream (at 10-15 km) which is higher than all birds except one type of vulture.

Edit: Nevermind, Google is working on exactly that: http://www.gizmag.com/google-x-makani-power-airborne-wind-tu...

The cable seems to be the most difficult part: http://en.wikipedia.org/wiki/High-altitude_wind_power

I find myself thinking of a grassy field swaying in the wind.

I wonder if they should try painting them deep green or something.

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