Vertical turbines are more efficient in large-scale wind farms: study | Hacker News Reader

Vertical turbines are more efficient in large-scale wind farms: study

eandt.theiet.org

266 pointskieranmaine162 comments

Wind turbine design engineer here:

There are several significant barriers to adoption that VAWTs face.

1. The wind resource is more powerful and more consistent higher off the ground. The hub heights of industry standard horizontal-axis wind turbines are reaching 135+ meters for the new generation of large offshore machines. These vertical axis machines are much lower to the ground.

2. Contrary to the claims of the authors in the Renewable Energy Paper (they say "The potential applications for VAWTs are endless, because the turbines are cheaper and easier to manufacture and maintain. "), vertical axis turbines have consistently had fatigue issues. There is an interesting history of the test-campaigns of vertical-axis machines at Sandia National Laboratories [1] that discusses this. In the 70s and 80s vertical machines were much more common than they are today.

3. It is a huge risk for an industry that is shipping proven technology to switch to a new paradigm that will require much more research and testing to work at scale. It's certainly possible and I find the possibility fascinating as a curious engineer. I would love to have a secure position developing VAWT tech or working on airborne wind machines (check out ground-based generator concepts to get an idea of where I think that will progress, not ill-conceived onboard generator kites like Makani).

The problem of wake blockage in large wind farms (and from adjacent farms to each other) is definitely significant though. The current "top" strategy is wake steering, where turbines at the front use their yaw drive to capture less power and allow for more power to reach the turbines in the rows following. [1]. The bleeding edge of this may be vertical wake steering, which can entrain high-energy wind from above the farm into the plant to capture more power [3].

[1] https://energy.sandia.gov/wp-content/gallery/uploads/SAND201... [2] https://www.nrel.gov/docs/fy17osti/68396.pdf [3] https://ieeexplore.ieee.org/document/7963037

Regarding the risk - I don't think this characterization is doing the issue justice. It's really about decades of building up a manufacturing capacity with suppliers, etc. to get to a position where wind turbines are now competitive because of this manufacturing capacity.

For an alternative to develop, it is not enough that it is slightly better. And both turbines driven by kites and vertical turbines are known tech, with known problems. They are likely not slightly better. Early wind pioneers knew about vertical turbines. They have some nice properties. But also some not so nice ones.

And this paper does not study vertical vs. horizontal as far as I can tell from a cursory look. It studies what happens with vertical turbines in a small farm.

Fair. I once was told by a senior NREL engineer that industrialization of a different concept than HAWTs would take over $1B in investment. Which is a lot in a low-margin, capital -intensive business like wind energy. And that number is probably on the low end.

Kites have the potential of much lower material costs to produce energy. If you have a pumping cycle kite, the "support structure" is the tether, compared to the tower and foundation required for a HAWT. The problems are indeed well known: 1. Tether material difficulties. 2. Need for self-launching 3. Airspace sharing problems at heights of kites 4. Controller design. This last one is what intrigues me personally.

The paper looks at vertical turbine arrangements, but the linked article about the paper starts with "The research suggests that the now-familiar sight of traditional propeller wind turbines may be eventually replaced by the sight of wind farms containing more compact and efficient vertical turbines." I had to respond to this rather wishful statement.

Do you have info/links on the current status of kite-wind-turbines ?

Obviously, they are unlikely to be ever competitive with current HAWT which is really sailing (pun!) along nicely.

But as a niche-player e.g. oil rigs, mobile power sources, etc, maybe not all is lost. What is their projects LCOE ?

EDIT: projected/promised $49/mwh

https://www.greentechmedia.com/articles/read/will-airborne-w...

I am interested in what has been done to study no-moving-parts wind power extraction.

Alvin Marks (who beat out Edwin Land for the polarized-sunglasses patent) filed a patent on this back in the '80s.

The idea is simple: you ionize air moving through your system, and the wind carries the ions away, accumulating a grid voltage vs. ground. The restoring current can do work. If your screen is on a kite, it can be very high up, to catch very high wind speed. It is very cheap to construct, with no mechanical parts at all; restoring current runs up (strictly speaking, down) the kitestring. Or, a screen could be stretched between upper parts of pairs of existing skyscrapers, or towers of a bridge, almost invisibly.

The trick is how to ionize air cheaply. Certain materials give up electrons to moving air spontaneously; you could have streamers of such materials, modified to be slightly conductive. Otherwise, you need some sort of charge pump to favor losing surface charge. Maybe a mist of water carries away the ions.

Measures of efficiency can be confusing. Ultimately, the measure that matters is W/$. If the installation is cheap enough to build and operate, percentage of available wind power extracted may be almost irrelevant. Stretched between existing structures, you might not want to extract much of the available energy anyway, because of the load it would place on the structure. But the next screen downwind could extract as much power, again.

what materials give up their electrons to moving air spontaneously? are there tricks you can do with the (perhaps nano-) patterning of this material, like arrays of little needles? have any labs attempted this? it looks fun.

I'm sorry, I am not a materials scientist. You might find a list of stuff not to use when building an antenna tower.

The big problem is resonances. A VAWT has various modes of resonance that are very hard to engineer against due to some of their basic properties. The largest of these, the one at Cap Chat in Quebec ended up being scrapped after an embarrassingly short period of operation.

There are some VAWTs in the rockies that lived for more than a decade but they made really little power compared to the amount of money that went into them.

But they look nice and are deceptively simple on paper (one less parameter to deal with due to the fact that you don't need to steer them, and the generator stays at ground level). So likely people will keep trying but it almost certainly isn't going to move the needle in the longer term.

If memory serves, the resonance problem with 3 blade turbines is when the blade passes in front of the pylon. But with the VAWT the blades instead pass into the shadow of every other blade, which is twice per revolution?

Does a VAWT behave better or worse in this regard with an even number of blades? Seems like with an even number multiple blades would occlude each other at the exact same time.

It is the tower occlusion that sets off the problematic resonance, which ends up eating the base bearings.

There are a couple of (small, obviously academic/experimental) vertical axis wind turbines near me which both have helical blades. I wonder what the tradeoffs for that design are?

Here's a picture (not mine) one of them: https://www.flickr.com/photos/nicephotog/25044930672/

For very tall VAWTs in a grid, could you dampen the resonances by tying the tops of the masts together with guy wires?

That will make it worse, not better. You want to decouple as much as you can so you don't end up creating a giant resonant structure.

They're sexy toys, not turbines.

See also: Windtree and other scams.

That reminds me of that recent finding that wind turbines would be a few percent more efficient if they turned anti clock-wise (at least on the northern hemisphere), but practically turbines in use today turn clock-wise. Sure, it should not be to much engineering to change that but still you need to adopt the entire manifacturing process to it.

Would you have a source for this? Really curious what might cause that.

I can't vouch for the sources, but here is some reading material:

https://wes.copernicus.org/articles/5/1623/2020/wes-5-1623-2...

[PDF] https://wes.copernicus.org/preprints/wes-2019-105/wes-2019-1...

https://www.economist.com/science-and-technology/2020/05/14/...

Interesting, so it's not the rotation direction of any individual turbine that matters but how the wake of turbines affect others around it.

Tangentially, I ran into the bladeless vortex concept recently (https://vortexbladeless.com/), do you have a take on that?

It seems like all your concerns/critiques from above would apply equally, but then I don't have any real expertise in the area.

I think the bladeless vortex concept makes no sense. Here's why:

1. The surface area of the machine is small. Think of this as the area that can capture power from the wind. Due to the cylindrical shape this is way smaller than the rotor area of a HAWT or even a VAWT.

2. Vortex induced vibration [1] is a real phenomenon that can extract energy from a flow. However, to extract this energy, the natural frequency of the structure must synchronize with the vortex shedding frequency of the flow around the structure. This is called "lock-in". Since the wind is a highly variable resource, it will not consistently be in this "lock-in" range in real-world conditions. To give perspective on the norm for HAWTs, pitch control for the blades is used along with generator torque control to achieve power production from 3 m/s all the way to the maximum (cut-out) wind speed of ~25 m/s.

[1]https://en.wikipedia.org/wiki/Vortex-induced_vibration

I guess you can "tune" the tower by adjusting a weight in the tower ... but I agree on the area issue.

Their website does scrolljacking that doesn't work on my browser. An idea is all appearances and no competence if they do that.

Not a wind turbine design engineer, but have done some fluid dynamics work. Thus, I'm not super familiar with what "wake blockage" is. A tentative look suggests that it might be similar to this work that I encountered[1], which suggests that by carefully positioning the wind turbines, one can extract more energy basically via the Bernoulli effect. Not sure if this is something of interest (or relevant) to you or not, but when I talked to some of the people working on that subject, it was implied to me that the manufacturers of wind turbine weren't interested in this, as it may decrease the number of wind turbines they can sell...

[1]: https://onlinelibrary.wiley.com/doi/epdf/10.1002/we.1806

Interesting paper. When I refer to "wake blockage", think of the turbines in the middle of a huge grid of machines. The energy in incoming wind on any side of the farm is mostly extracted by the outer turbines. The inner turbines typically produce ~15-20% less energy due to this effect. Also, the wind hitting them is more turbulent/"dirty" as it recovers back to free-stream velocity behind the front row of machines, which can cause abnormal fatigue patterns.

That's definitely of interest to me, although I think that manufacturers are interested in it. Many manufacturers are very conservative with installed/environmental conditions of their production machines and want to minimize risks, instead of potentially alienating a developer by suggesting a scheme that could fatigue turbines or have other unintended consequences. If anything, the paper suggests to me that if adopted, manufacturers could sell even more turbines!

It's very possible that I misinterpreted the situation as effectively I got to this information through an overheard in discussions with other fluid dynamicists in school. I thought the information presented is kind of interesting, so I was surprised that no one continued to pursue this avenue of research. I'm glad that you find this interesting, perhaps this knowledge could be put to good use. Although, there may be there are other factors that I'm not aware of impacting the real world performance of this, as my specialty is not in wind turbines (not yet anyway).

FWIW, I know that Vestas has a department with a super computer dedicated to helping their customers choose optimal positions. And I also know of some recently commissioned large wind farms where the company behind explicitly mentioned wake optimizations. All the big turbine manufacturers are in an optimization race.

That's interesting to know. I didn't know that turbine manufactures are that state of the art. I mostly thought they are just building some sort of standard turbines and deploying it to different places like building houses. Evidently I'm mistaken. Perhaps I should investigate this area a bit further...

Can you use huge regular turbine to vertically steer wake in to array of smaller vertical turbines?

What about Gorlov helical turbine designs?

That is surprising. They have an inferior efficiency already due to the Betz limit (it is proportional to surface area facing the wind) and will always be about 60% max for a HAWT and worse for VAWT. However, the dynamics of turbulance have been one of the hardest things to model in large wind farms. The article is a bit light on details, but the last time I went to the Sandia Labs wind turbine conference in Albuquerque, VAWTS were nowhere to be seen (2015) and the biggest modeling challenge was large farm interferrence. Very interesting.

Betz Limit: https://en.wikipedia.org/wiki/Betz%27s_law

https://youtu.be/EM-gCvhQhPU?t=508

This lady says Betz limit doesn't apply to VAWT.

Huh, did not know. Thanks for the link. Kind of disappointing, I was hoping for an explanation, not a claim.

This paper has some insight:

https://iopscience.iop.org/article/10.1088/1742-6596/753/2/0...

I suppose I could have Googled instead of complaining, so thanks for doing the work for me! :) [I like how the first citation is from a 1920's paper (by Betz).]

I keep wanting to read that title as: Vertical turbines far more efficient than large-scale wind farms

But then you read up and it's really: Vertical turbines far more efficient when in large-scale wind farms than they are individually

Whether they can ever be made to be efficient enough to make sense seems to be the question.

> Vertical turbines far more efficient when in large-scale wind farms than they are individually

The article is saying that in large-scale wind farms, vertical turbines are more efficient than horizontal axis wind turbines (the "traditional form factor").

With horizontal axis turbines in large wind farms, there is always a loss of efficiency through the "wake effect" where some of the turbines are downwind from the others.

But the study seems to have found that this can actually increase the efficiency of vertical turbines. Which is very unexpected.

> The article is saying that in large-scale wind farms, vertical turbines are more efficient than horizontal axis wind turbines

Is it? So much for my reading comprehension score today.

ETA: I read the underlying paper this time (https://www.sciencedirect.com/science/article/pii/S096014812...) and I'm fairly certain what it's actually saying is:

Vertical turbines far more efficient when in large-scale wind farms than they are individually, and furthermore their increase in efficiency can be greater than the increase in efficiency readily attainable by HAWTs because VAWTs can be placed close together and gain downstream efficiency, whereas HAWTs can't be placed so close together and even when relatively far apart lose downstream efficiency due to turbulence, but YMMV depending on local conditions and other factors, for example: the steadiness of the wind, because VAWTs often need a boost to start from a stop.

Which is probably not the title they wanted to use, eh? Imma hop in my boxy but safe Volvo and go watch "Crazy People" again now.

Yes, I think your reading is correct. The article makes claims the paper does not about comparing Vertical vs. Horizontal wind turbines.

If they really are more efficient in lower velocity wakes wouldn't it suggest putting them as a second line?

It would probably make a bigger wake and of course would eventually experience diminished returns if you tried just adding more lines.

Initial hot take: I'm not sure they're measuring efficiency in a way that's really meaningful to me?

There are so many ways you could measure it. You could measure it as the % of wind energy passing through the turbine's plane that is taken out of the air, or the the efficiency of using that energy to get the rotor turning, or the efficiency of converting the rotor's kinetic energy to electrical energy.

(edit: Or I could, y'know, do the sensible thing and check the article. They're measuring power output for a given wind speed and direction. Which I think means, in effect, all of that end-to-end.)

But I'm not sure any of those are, in and of themselves, what really matters at scale. The more interesting questions, I'm guessing, are things like, "How much energy can we get out of a plot of land of a given size?", or, "How much energy can we generate for a given cost to install and maintain?" Both of which, I would assume, are more difficult to directly extrapolate from thermodynamic efficiency in wind turbines than they are for something like photovoltaics, because of the "moving parts" factor.

I think this is efficiency in terms of much energy you can extract for a given area of sea or land. Wake effects mean that wind turbines cannot be placed in a particular zone downwind of another turbine. If wake effects are lower then you could potentially get a higher density of turbines in a given area. This is something that is already considered in terms of turbine height and placement. Sometimes they are placed at closer intervals along the perimeter of the zone and then lower densities within.

Of course lots of factors are considered with the final "efficiency" being about getting the highest return for an investment.

If land is your dominating cost factor, its how many kw per acre can you generate. So dense circular turbines seem good.

If the cost to produce the turbines is the dominating cost factor, and traditional turbines are "cheaper" to build, it could be a win in some cases to use more land with normal wind turbines. The more you spread them, the less problem you have with wake on downstream turbines.

Or it could vary based on land value of where you are installing a given plant.

But land value depends on what you can do with the land. It will always going to be more profitable to build a distribution center or yuppie condo but most sites cannot accommodate that. Wind turbines make sense when a land owner is trying to make more money out of an existing asset. Maybe it is moorland with sheep on it. The wind turbines supplement existing land use and give an extra source of revenue. The developer is competing with other developers. Once they have a land owner on board they will have a certain target they want to hit and will try and get away with as much as possible.

> "How much energy can we get out of a plot of land of a given size?"

I don't believe this is an answerable question in this format. The size of a plot says nothing of land topography, nor the average wind currents for any given timeframe.

Wind farms are great tech, but adequate calculation of efficiency and cost/benefit is always subjective to individual installations. Solar farm efficiency calculations are easier because the variables at play are much more consistent. Essentially: panel efficiency * sun exposure * array size. I don't believe this formula translates to wind farms.

Finding a more efficient design for wind-to-energy conversion is a lot like making an improvement in the "panel efficiency" part of solar arrays. Or maybe wind has an "array design" variable to consider since one turbine's design can affect the wind energy capacity of another. This isn't the same for solar, unless panels overlap during certain times of the day.

Yeah, that's more or less what I was getting at, albeit in less detail. Put topography and how it interacts with the wind and all of that under the category of "mechanics", I guess? But, in the simulation that this study is based on, it looked to me like they assumed flat terrain and laminar airflow coming into the field of turbines. Which I'm assuming happens in nature approximately never.

So it's like, sure, maybe this turbine arrangement can get 15% greater power output under ideal conditions, but I don't think you can get from there to, "this is a clear win over the incumbent technology" anywhere near as easily as you could in the case of an photovoltaic efficiency improvement.

The article seems to be talking about the efficient use space (sea area). However, speaking as a layman, these vertical turbines appear to be structurally more complex and to consist of more material, so I would expect them to be more expensive per MWh.

Would they be more efficient than traditional horizontal wind parks when looking at total cost of ownership?

On the other other hand they seem mechanically simpler because the entire turbine doesn't have to be mounted to pivot depending on the direction of the wind, and the column that holds up the turbine and blades is much shorter.

The short height is a serious problem.

I think we can make some conclusions about the power output for a given material input. Based on the the images, my assumptions are: 100m mast and 80m blades; for the vertical turbines, a radius of 50m. The blades look to be lighter weight, but the mast looks heaver weight, so say the two styles use similar amounts of materials. Also, windspeed is logarithmic with height.

Wind power goes as the cube of wind velocity over the swept area. With my assumptions, the vertical turbine outputs about 2.7MW, while the horizontal turbine outputs about 8.4MW. The reason is height: it helps to have the blades sweep more higher altitudes wind, where it's faster.

These might be easier to pack tightly into a windfarm, where the metric that matters is W/m^2. But most of us care about W/kg because that is proportional to W/$: the winner looks to be horizontal turbines because they reach higher.

A hybrid of horizontal behind vertical might be interesting. There are diminishing returns to how "deep" you can make your windfarm: the trailing edge suffers from turbulence from leading edge, and these could work better in turbulence.

Also the generator can be at ground level, rather than having to perch at the top.

Don't quote me on this, but I recall reading that there is a layer of air at ground level that is very turbulent/choppy due to it's interaction with the ground which makes it terrible for wind power generation.

What the parent-post means is that the machinery of the generator is positioned at the bottom below the blades instead at the top of a tall column behind the blades. Presumably this creates some savings in terms of construction and maintenance.

perhaps also aerodynamics relative to a big generator blob right at the top?

Only the generator is at the bottom, the power still comes from the upper part of the structure and is transferred mechanically, I would assume.

VAWTs do ok in turbulent conditions. HAWTs don’t like it because they need a consistent stream of air flowing in one direction.

General fluid speed is ~0 at any surface and has some gradient to the proper wind speed as you get some distance away from the surface.

However the variability of physical forces on the blades as they rotate means the materials have to have properties that make them less brittle or prone to fatigue due to these conditions. Those materials I think are mor expensive than those on traditional blades.

Generally, turbine farms are built where the wind mostly comes from one direction. When the wind is not in a favorable direction the turbines are idle.

Why would they be idle? They can pivot for a reason and I haven't seen turbines very close together in any direction. Sometimes they are indeed arranged in a long row, but even then, why not use all the wind energy they can get? I could imagine problems with turbulence and mechanical wear close to maximum design wind speed and yeah, they might shut down then.

>Why would they be idle?

Sometimes they are idle not because of the lack of wind, but because of the lack of need for the electricity. When power demand is low, the wind turbines are the first things to be stopped. In fact, they use an electrical braking system to keep them from turning. The power companies say that it is much easier to stop/start wind turbines than lower/raise the output of gas/nuclear/coal power plants.

GP is asking why the turbines would be idle if the wind isn’t coming from a particular directions. They’re not asking for a list of unrelated reasons for why a turbine might be idle.

> When the wind is not in a favorable direction the turbines are idle.

Actually:

>Why would they be idle? They can pivot for a reason

It seems to me you are reading into the post something not there. The person I replied to, quoted above, did not ask what you asked, and actually stipulated that HAWTs do pivot to turn into the more favorable direction.

In the Texas panhandle along Interstate 40 west of Amarillo there is a continuous east-west line of wind turbines running about forty miles. The turbines face north because the wind is almost always from the north and the turbines are there because the wind is almost always from the north. Each turbine is placed to avoid casting its wind shadow on the other turbines...there are typically three or four banks of turbines from north to south.

Suppose the wind shifts to the east, enfilading all those miles of turbines. It’s a turbulence nightmare. But fortunately a rare event. An edge case where idling makes sense and staying online doesn’t.

At the extremes of nacelle yaw, the upwind turbines may cast a wind shadow on a downwind bank. Again an edge case where idling some turbines is a reasonable tradeoff.

These are networked smart devices. And humans in the loop monitoring and tweaking.

Can you comment on https://weatherspark.com/y/4750/Average-Weather-in-Amarillo-...? It suggests that although during winter north and west are the strongest wind directions, in the summer you get south winds up to three quarters of the time, and precious little north wind at all.

This is pretty consistent with my loose understanding of how these winds work and my experience in south east Australia: the predominant wind directions vary very significantly by season, and even within seasons substantial deviation is much more common than people often think.

Amarillo is near the eastern edge of the Llano Estacado. The large wind farms are to the west on top of the mesa.

The Llano is the southern end of the High Plains that extend all the way into Montana. As it passes the Rockies the Jet Stream tends to bend south. Further east the weather is more varied.

Or to put it another way, its a fair bet people settled in Amarillo for its less horrible weather. There’s not a major city between it and the Rio Grande at Albuquerque 450km to the west just some small towns here and there mostly where the railroad did something interesting.

The Llano and the high plains weather patterns are dominated by macro scale climate patterns. This is why the large wind farms are there.

Indeed, we have lots of space. The more important efficiency is turning capital into electricity. I believe horizontal turbines still have the edge here. This could possibly change if produced in enough volume to get the manufacturing costs down - it depends if they have an advantage in materials use, install and shipping costs, and maintenance costs.

> vertical turbines boost each other’s performance

Meanwhile, horizontal turbines impair each other's performance when they sit in each other's wake.

I remember reading that the loss of power generation was more than previously expected, as you increase the area of the wind farm?

So, it could be financially worth it to optimise vertical turbines, if they work in a more synergistic way.

I would take that claim with a pinch of salt unless they're able to explain the physics of how one turbine suffers in less energy dense, muddy air whilst another thrives.

I can imagine there's a difference in wake from a classic turbine blade that slices through the wind coming at it, and these vertical ones that are sort of pushed out of the way.

"Classic" 3-blade HAWTs (the same style as modern off-show wind turbines) are aerofoils, they're working on lift - like a sailing boat or glider - and are surprisingly narrowly angled to wind direction.

Darrieus VAWTs are operating by the same mechanism for a deal of each blades rotation.

Unless you're thinking of "American" style wind turbines that used to drive water pumps, which are like like water wheels and closer to Savonius VAWTs in operation.

I think people often mistakenly think of 3-blade HAWTs as working principally in the same way as a anemometer.

Here's a machine-translated post on vertical turbines by one of the pioneers in the modern wind turbine market:

https://translate.google.com/translate?sl=auto&tl=en&u=https...

TLDR; they have been tried out and found impractical.

I'll add to that that many, many years have gone into the manufacturing of current big wind turbines. Making something that can withstand the weather, have a high uptime, relatively cheap to manufacture and put up - these are not easy problems.

I'd caution generally against the argument that "it has been tried before and didn't work." There are undoubtedly value lessons to learn from earlier attempts. But "don't even think about it" is almost never one of those lessons.

I would kindly ask you to read the article I linked to before passing judgement on my extremely short summary.

I skimmed the paper, and its contribution is a study on how vertical turbines seem to behave in a very small turbine farm. It does not study whether vertical turbines make more sense than horizontal. But the only reason we see it here, is because this article makes some pretty big and unfounded statements about the current horizontal wind turbine approach.

So we're here because of misinformation.

Additionally the larger ones appear to need guy-wires to presumably prevent the whole structure from wobbling as rpms increase.

I think its also reducing the losses of turbines in the lee of other turbines.

Has any research been done on the effects of wind farms on local wind/weather patterns? It seems like taking energy out of the wind in a relatively concentrated area would have downstream effects.

(I'm not anti-wind energy, I'm just curious).

Yes,

This is my favorite infrastructure project concept: https://www.scientificamerican.com/article/offshore-wind-far...

help with hurricanes, direct DC to the entire country, tons of jobs for maintenance, etc

There's some research that wind farms at scale have a small but non-negligible warming effect:

https://www.sciencedirect.com/science/article/pii/S254243511...!

Wind encounters far more resistance and obstacles when sweeping over land, ex. cities with buildings (tall and small) and other man made structures and then there are various natural ones - trees, hills, etc.

Windmill probably is much less of a drag (pun!) as compared to above.

Yes, research has been done, if only because knowing about that is essential for figuring out at what distance from each other you should place your turbines.

See for example https://energyfollower.com/wind-turbine-spacing, https://ep.liu.se/ecp/057/vol15/014/ecp57vol15_014.pdf

i'm not aware of any comparisons but imagine a sparse forest.

I think offshore wind farms have been proposed to protect the US from hurricanes. So apparently they substantially decrease wind energy.

> offshore wind farms have been proposed to protect the US from hurricanes

No, certainly not seriously.

https://news.stanford.edu/news/2014/february/hurricane-winds...

An estimate of 78,000 turbines is truly a thought experiment, not a realistic solution. There does not exist manufacturing capacity or installation capacity to achieve this (not even remotely close). The offshore wind pipeline, globally, is orders of magnitude fewer WTGs, and procurement & installation pressure is already expected to be very tight in the coming decade.

This is made more difficult in the US due to the complexities of offshore wind installation imposed by the Jones Act.

It’s a neat concept. But it will never be realized.

An interesting thought I've wondered about as well. I imagine the risks outweigh the benefits. I would think the same thing would happen when planting a forest (granted it taking much longer to produce an effect)

VAWTs suffer from 2 serious drawbacks: 1) they're crap at starting up - i.e. going from stationary to moving - and usually need some supplementary help to do so, and 2) they're noisy - as in noisy as hell! I wouldn't want one within 500m of my house.

I recall seeing report of a similar result many years ago (at least 10, perhaps much more) where VAWTs deployed in complementary pairs were shown to be more efficient, so this looks like a repeat /rediscovery of the same result.

I think there may have been turbines with those two problems but that does not mean that all turbines are like that. Merely that there were some issues to sort out back in the day when you read about someone allegedly having these issues.

Basically, noise would indicate either some problem with loose parts, a lot of friction, turbulence or something else that is clearly being inefficient. Obviously to compete with state of the art horizontal turbines, you'd use highly durable materials with awesomely low friction and generally be shooting for very high levels of efficiency.

Some other things I've seen suggests that small vertical turbines are suitable for deployment in urban environments where they work with low/variable wind speeds at completely acceptable noise levels. You could put these on your roof even. I left a link elsewhere in this thread if you are interested.

Basically the article is about a group of scientists that ran the numbers and came up with different conclusions than you. 15% more efficient is quite a lot.

What's the source of the noise? The turbine itself? the air flow around the blades?

My guess (and that's all it is) is that it's the airflow around the blades -- it's a loud humming noise, present even on an unloaded (no turbine) VAWT. Much the same way that ships' propellers create noise: it is primarily generated by the blade causing a partial vacuum behind the trailing edge of the blade, and the collapse of that vacuum creates the noise.

My guess is the return stroke of the blade sounds like a helicopter

Hadn't thought of that, but the blades are going to be slapping the wake of the upstream blade 3-4 times per revolution. The helical blade style probably help with that quite a bit though.

It'd be easier to sort out with all of the videos uploaded to YouTube if humans were capable of not adding cheesy soundtracks to everything.

And would it still be an issue if they're in the sea?

Noise pollution is pretty harmful to sea life, especially cetaceans.

https://oceanservice.noaa.gov/facts/ocean-noise.html

how much air noise transfers into the water though?

I would guess that would increase the infrastructure/cost for transmission if you have to put them further out to sea.

Where I live the turbines are already quite far out, I don't think I'd be able to hear them if they were of the vertical kind.

95db over water could be heard from a couple miles away, especially if the atmospheric conditions are right. I don't know how far out the current ones are since we don't have any around here.

This brings up another interesting point. If there are concerns around ship engines and submarine sonar or ELF for marine life, I wonder if any testing has been done concerning that with the turbines.

In the UK wind farms are usually put in the sea.

At a guess: the wobble/precession/oscillation of a turning column only anchored at one side, but sticking up into the wind.

All large wind turbines are loud. Like, unbearably loud.

I don't believe this is true. There's an installation of 9 1MW turbines (perhaps quite small in comparison to the largest ones around today) near where I live that I frequently cycle past (within ~50m). Even in strong winds they are barely audible.

how audible wind turbine also depends on which direction the wind is blowing

That's interesting. Hydro is crap at startup too (they need black start units, at least the big ones do) [What I wrote here about black start was pretty much wrong, not sure what I was thinking] so maybe that's not too big of a problem, but that sound thing seems bad, even if the units are out on the water. Those things are loud, I had no idea!

"The noise emission from the wind turbine was measured, at wind speed 8 m/s, 10 m above ground, to 96.2 dBA"

https://www.mdpi.com/1996-1073/9/1/19/htm

[Edited to add: What I wrote about hydro black start units was really wrong, I wasn't thinking when I wrote that, it needs far more detailed explanation like the comment below.]

> * Hydro is crap at startup too (they need black start units, at least the big ones do) *

This is a misunderstanding. All generators require an excitation current to start up. Most generators get this excitation from the grid. For large, important generators they also have black start, so that they can provide excitation on-site. This means they don't need to bootstrap themselves from a grid.

Hydro tends to have black start not because 'they need it' but because it is critically important from a grid security perspective. During a blackout, you want your high inertia, flexible machines online first - these are hydros for systems that have them. If you don't have blackstart on these machines, you need them on some other machine online first to energize the grid.

You wouldn't put blackstart units on wind turbines, simply because they are worthless if there isn't already an energised grid to support into (they aren't grid forming). So you can always assume grid-based excitation current for wind generators.

I think OP was talking about the cut-in speed (at what wind speed can the turbine start producing power). For HAWTs this is at wind speeds of around 5 m/s. For VAWTs, I don't know, but I assume it is a little higher based on the OP's comment, and that they may even need some mechanical assistance to get them spinning in the first place.

Nuts, you're totally right. I really know better, not sure how I got that so wrong.

Are you sure about that, because I was just reading the Black Start Wikipedia yesterday and it listed Hydro as one of the best at requiring little start up power. Hydro is often the Black Start source for other power plants.

I am sure I was wrong :-)

The paper you linked suggests that horizontal turbines are even louder:

“The noise emission at 6 m/s 10 m above ground was measured to 94.1 dBA, this while while operating at optimum tip speed. Available noise surveys performed on similar sized operating at optimum tip speed. Available noise surveys performed on similar sized HAWTs [27–30] HAWTs [27–30] has established noise emissions of 95.1–100.2 dBA and 97.3–102.4 dBA for 6 m/s and has established noise emissions of 95.1–100.2 dBA and 97.3–102.4 dBA for 6 m/s and 8 m/s respectively”

Land use efficiency is not the same as economical efficiency. Arguing that we should build vertical turbines because they are more land-use-efficient is silly, because land is cheap where we build wind farms.

The only efficiency that matters is power generated per dollar invested. And if these vertical turbines were more efficient that way, then we would already be using them widely.

Not every part of the world has large amounts of cheap land available for wind farms. Land use efficiency is important there.

It's my understanding that vertical turbines need far less height to be effective. If you can get away with moderate towers on various existing structures, then the amount of available land increases dramatically.

Maybe the reason they are cheaper is simply because they have a head start on building the supply chain and manufacturing process?

since the article doesn't say or show what a verticle axis turbine is:

https://www.researchgate.net/publication/333316757/figure/fi...

Wikipedia is also helpful:

https://en.wikipedia.org/wiki/Vertical-axis_wind_turbine

https://en.wikipedia.org/wiki/Wind_turbine#Horizontal_axis

You could have horizontal axis turbines with half of them rotating clockwise and half anticlockwise, though it seems the effect is minor, less than 2%:

"counter-rotating configurations were more efficient in power generation than the control case in which all turbines have one clockwise rotor; the alternate-row case was found to produce 1.4% more power "

https://www.sciencedirect.com/science/article/abs/pii/S22131...

Overall there's probably a lot of ways left to optimize on wind farm level. For example the yaw angles https://www.sciencedirect.com/science/article/abs/pii/S03062...

And just when I was imagining twiddling my thumbs in opposite directions...

Serious question. I live in a hilly area where there's a lot of wind much of the time. Is there some kind of residential analog to rooftop solar I could install? Or is the infrastructure just too expensive and complicated for a hobbyist?

You can buy something in the 1-3 KW range at Home Depot. I've seen one in person at an off-grid house and the owner couldn't understand why people even used solar. This was 15+ years ago though, so solar was MUCH more expensive than today while a turbine I'd imagine was about the same?

I suspect the intermittency of wind is higher and requires a decent amount of energy storage to smoothen the output. As energy storage gets cheaper, probably off grid installations can complement their solar installations with wind as well, depending on the location.

I assume it'd be super expensive to grid tie it though, right? Sorry. I'm a total noob at this stuff.

Residential wind power? Wind energy is something that greatly benefits from scale: it’s why the current and next generation of turbines have rotor diameters exceeding hundreds of meters. You’d probably be much better served by using solar panels.

Sure. I just meant for fun or for a project. The biggest cost is probably grid tying, right?

John Dabiri (referenced and thanked in the study) and his team have been researching this topic for a long time: https://dabirilab.com/

>“Modern wind farms are one of the most efficient ways to generate green energy. However, they have one major flaw: as the wind approaches the front row of turbines, turbulence will be generated downstream. The turbulence is detrimental to the performance of the subsequent rows.”

Yes, this is called a 'wind shadow' and it relates to the slower, turbulent, dirty air coming out of the back of a wind turbine being less energy rich for the turbines behind it. Wind farms are designed to minimize wind shadow impacts based on prevailing wind directions.

> “[VAWTs] can be designed to be much closer together, increasing their efficiency and ultimately lowering the prices of electricity. In the long run, VAWTs can help accelerate the green transition of our energy systems, so that more clean and sustainable energy comes from renewable sources.”

This sounds like it will make the wind shadow effects worse.

> The research found that VAWTs increase each other’s performance when arranged in grid formations

This seems like straight bullshit, and is really unclear. The argument seems to be that VAWTs are somehow positively impacted by wind shadows?

The air coming out the backside of a turbine (VAWT or HAWT) is less energy dense and more turbulent, so the results seem fundamentally flawed. The best design is one that minimizes the amount of 'wind shadow' being swept by turbines.

I am entirely unconvinced.

> The argument seems to be that VAWTs are somehow positively impacted by wind shadows?

I'm totally wild-guessing here, but from the header image it looks that they place them in rows with a light offset, with free air-flow channels in-between. Considering the look of the wings, this actually might use the shadow effect to improve the performance, as they role like Tibetan prayer wheels, in succession, where one side is pulled by air going through the channel, while the other half (the one going against the wind direction) is in the shadow which is reducing the negative push.

If you want to have a look at the study, it is linked from the article.

I'm not an expert, but I thought one of the main advantages of vertical turbines was better usage of rapidly changing wind

VAWTs have a better tolerance for turbulence since they don’t need to face into the wind. They also continue to operate in gusty conditions. They do have downsides but make up for it with a smaller footprint, reduction in moving parts and the advantages listed above.

The paper's here, if you want to see how they came to the result. The PDF is paywalled, but you can view it in their online reader for free.

https://www.sciencedirect.com/science/article/pii/S096014812...

Properly understanding it is well beyond me, but it looks like it's about carefully arranging the turbines with respect to each other's wakes. While this is based on modeling and not empirical experimentation, it doesn't look like they just pulled the idea out of a hat. Getting the 15% improvement seems to require that the pattern is optimally oriented with respect to the wind direction, so I'm guessing real world benefit wouldn't be anywhere near that great.

You can download the paper using the download button in the top right corner of the online reader's menu bar.

Direct link: https://www.sciencedirect.com/science/article/pii/S096014812...

Perhaps the new design somehow reduces the shadow effect by extracting wind energy from higher layers of air?

This company has been slowly developing vertical wind trubines: https://windside.com/

They are not (yet) for mega installations, but since they are almost silent and maintenance free they can be used both in urban areas and in sahara/antarctis where things just have to work.

The "Just have think" youtube channel did an episode on VAWTs just last week: https://www.youtube.com/watch?v=gcSnwW5v3f8

Vawts are mechnically quite simple and compact. You can put them just about anywhere. And they can operate even at low wind speeds, regardless of where the wind comes from.

There's a company experimenting with these along highways to get energy from vehicles driving by. The idea here is to simply wrap them around existing street lights. Not a lot of energy per turbine obviously but it adds up if you do it along a few miles of highway. And they are cheap, small, lightweight, and easy to install.

Nice video.

> There's a company experimenting with these along highways to get energy from vehicles driving by.

Those turbines will be slowing down the windflow, causing extra resistance for the traffic. The video doesn't mention that. Does anyone know if that effect is significant enough to reduce or even reverse the overall benefits (especially given the large % of ICE vehicles)?

The ancient windmills of Nashtifan continue to be vertical to this very day. https://www.youtube.com/watch/3qqifEdqf5g

If you look at the actual study[1] it's not just vertical turbines but also their formation [2]that (could) increase efficacy of large-scale wind farms.

[1] https://www.sciencedirect.com/science/article/pii/S096014812... [2] https://ars.els-cdn.com/content/image/1-s2.0-S09601481210034...

The vertical turbines are not more efficient in themselves. In fact, they are less efficient. The paper does not claim that they are more efficient overall in a farm configuration either, just that they somehow seem to get a positive effect when placed in a (very small) farm.

>For the configurations analysed, pairs of VAWTs exhibited a 15% increase in power output compared to operating in isolation, when the second rotor was spaced three turbine diameters downstream and at an angle of 60° to the wind direction.

This seems like a major limitation of the finding. The wind direction is variable. If your clever idea only works when the wind is blowing exactly west, it's not so clever.

From figure 6 in the paper, it looks like you get the win for anything from 30 degrees angle upwards. But with 0 degrees angle, the turbines seem to interfere, and you get something like 50% loss. So with a westerly prevailing wind (from 270 degrees), you'd likely put the turbines in rows at 210 or 330 degrees. If you used 210 degrees, and the wind comes from 210 degrees, you lose. Almost all the rest of the time you win. With some simple analysis of historic wind directions, you ought to be able to choose the angle to maximize net output by putting the inefficient angle in a direction that is relatively uncommon.

But in areas where the wind farms are built, isn't one of the deciding factors that the wind primarialy blows in one direction? Similar to airports and how they decide which way to build their runways. LAX doesn't even have North/South runways because of this.

Wind is rarely exactly in one direction. A constant west wind isn't always directly 270 degrees, there is a large plus/minus factor in that.

Wikipedia has pictures if like myself you have no idea what a vertical wind turbine looks like: https://en.m.wikipedia.org/wiki/Vertical_axis_wind_turbine

So does the article.

You mean that header image? It's super small on my phone.

I hope these researchers don't stop with just writing papers, and actually see if they can convert their theory into practice. If it's true that there's a far more efficient way to run wind farms, it seems like it could be a huge profit opportunity.

Unfortunately they don't have video of the fluid flow simulation.

The effect must come from vortex interaction or syncronization and it would be interesting to see. If there is some form of strong coupling it may increase efficiency but induce vibrations.

I’ve been wondering why we don’t have these on top of our street lights. I imagine a street light with a Darrieus vawt on the pole under the light and a small solar panel on top.

Noise, maintenance, added cost and complexity. Then you also have the issue that you need an inverter and some kind of scheme to communicate with the mini wind turbines so they don't drive the voltage too high or some other kind of scheme for regulating that.

because a whole city with turbines on each street light might produce the same amount of power as 1 large scale wind farm at a fraction of the maintenance cost

https://www.youtube.com/watch?v=gcSnwW5v3f8

There is a roadside vertical turbine concept which seems promising. It uses lampposts as a mounting point, reducing materials needed, reusing existing cables in the lamp, and scavenges energy from trucks thundering by. And since it's in a developed area, you don't affect existing views.

The new Siemens offshore turbines put out up to 16MW. This has blown me away. Tho, they are scary machines and I get uncomfortable looking at them (like single balcony on a huge wall kind of uncomfortable). Aesthetically the vertical ones are much, much better IMO. Especially if they can be placed in an symmetrical pattern, not this super optimized complex mess traditional ones show.

The vertical axis turbine seems like it would scale in size better since the blades are spinning perpendicular to gravity

They are subject to much higher dynamic forces, rapidly cycling between windward and lee side. Vertical turbines have worse wear characteristics, and it only gets worse as they get bigger and need more massive airfoils.

Do they have one shape or multiple? I tried searching for a photo of one but getting a mix of results.

So this reflects economy of scale (more turbines per area) rather than higher output/turbine, right?

wind sails (kites) are the future

absolutely not. I'm sorry makani went under (there's an excellent documentary about them on YT), but when you compare their extreme complexity for a "simple" 600kW unit to newer wind turbines that are now reaching 10MW, you'll see why

Skysails Power is shipping.

Per their datasheet, the SKS PN-14 produces 80-200 kW. Now compare this to a modern Vestas V164 8000kW turbine. The latter seems way simpler engineering-wise to me

You are comparing a 20 tonnes system to a 1300 tonnes system

But then having a nominal capacity of 8000kW from the 20mt system, you’d need maybe 1200 tonnes of the 20mt systems.

I’m not sure how that’s better or simpler. Sounds vastly more complex and expensive.

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