Breakthrough research for testing and arranging vertical axis wind turbines

February 28, 2017, American Institute of Physics
The Shepherds Flat Wind Farm is an 845 MW wind farm in the U.S. state of Oregon. Credit: Steve Wilson / Wikipedia.

The sight of propeller-like rotating blades positioned high up the pole of a tall horizontal-axis wind turbine (HAWT) may be familiar to many. Often grouped in wind farms, HAWTs provide significant amounts of energy for local communities. One drawback to HAWTs is the large space they take up, needing to be placed far apart from each other. If placed too close together, the turbulence and wind velocity deficit caused by one HAWT can make a neighboring HAWT output much less power.

To address this, researchers are looking at vertical-axis wind turbines (VAWTs), which could be either arranged in groups or interspersed within HAWT arrays. A VAWT has an overall cylindrical shape, with the blades aligned parallel to, and rotating around, the pole on which the rotor is mounted. These "egg-beater" VAWTs tend to be much smaller than the "propeller" HAWTs, typically about 10 times shorter in height, and output only about 0.1 percent as much power per turbine.

Anna Craig, a mechanical engineering doctoral candidate at Stanford University, and her research team recently studied modeling VAWT arrangements, the results of which they report this week in the Journal of Renewable and Sustainable Energy.

While a single VAWT is not as energy-producing as an individual HAWT, the wind flow synergies created in a closely-spaced array of VAWTs can potentially generate up to 10 times more power per unit of land area than an array of widely-spaced HAWTs.

"For the vertical axis wind turbines, what you get, especially as you place them in close transverse proximity to each other, is that they can actually interact positively," Craig said. "Although it is still an active area of research, we think that the VAWTs can have blockage effects causing speedup around the turbines that helps downstream turbines. They can also have vertical wind mixing in the turbine's wake region, which assists in the wind velocity recovery."

Craig said researchers agree that there is more research to be done on VAWTs before they can be deployed at an energy sector scale. However, Craig and her colleagues provided significant insights into one central VAWT challenge: how to research, test and develop insights for effective array arrangements. They did this in a lab experiment because field testing is currently very expensive, and computer simulations are not yet refined enough or are too computationally expensive.

"Right now the majority of numerical simulations are either fully two-dimensional or are three-dimensional, but use highly simplified, effectively two-dimensional models for the turbines. Neither approach can capture the vertical flows, which are critically important in the energy dynamics of a VAWT system," Craig said.

Craig and her colleagues believe that this and similar follow-ups offer important possibilities both for in-field arrangements and refining numerical simulations. They conducted the experiment in the large water flume at the Bob and Norma Street Environmental Fluid Mechanics Laboratory in the department of civil and environmental engineering at Stanford, with the system's water flow effectively representing the wind flow.

Craig set up roughly 1,300 1-inch gears between plates, which were reconfigurable during the experiment. On top of these gears sat approximately 300 rotating cylinders mounted to create a 10-foot-long array, with the cylinders effectively representing VAWTs. They tested a total of 10 different arrays with different configurations.

"The three variables I was looking at were spatial configuration, rotational configuration, and height configuration of the elements," Craig said. "I wanted to find out how the interactions between elements could set up larger scale flow patterns."

The experiment illuminated the VAWTs' time-space averaged vertical flow, which is significant for turbine arrangements.

"What I saw is this net vertical flow from above the array, down into the array and out the sides of the array, which was somewhat unexpected." Craig said. "These net vertical and transverse flows eliminate horizontal homogeneity within the array and introduce a new mechanism by which the energy resource within an array can be replenished."

For future studies, Craig said this experiment offers important insights for both numerical and in-field testing.

"The three-dimensionality of the flow through the array is critical to understanding the energy dynamics of the system," said Craig. "This paper really focuses on allowing us to design appropriate numerical and experimental studies."

Craig is optimistic about VAWT technology and its potential uses, noting that in the future it might be interspaced within HAWT arrays and brought to places that are not amenable to the much larger HAWTs, such as islands and cities. She says that VAWTs could also potentially be less environmentally impactful than HAWTs.

"We should consider numerical or even field experiments with larger numbers of VAWTs because the laboratory experiments have shown that the physical mechanisms are there for these larger arrays of turbines to work," Craig said.

Explore further: The improved Savonius wind turbine captures wind in the cities

More information: "Low order physical models of vertical axis wind turbines" Renewable and Sustainable Energy, Feb. 28, 2017. DOI: 10.1063/1.4976983

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25 comments

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gkam
2.5 / 5 (11) Feb 28, 2017
They are also more interesting-looking.

We had several types on a hillside here in the bay area for a while, and some that looked like airfoils on a moving clothesline.
WillieWard
1.7 / 5 (11) Feb 28, 2017
They are also more interesting-looking.
Interesting looking them slaughtering birds and bats in midair and displacing wildlife from their natural habitats.
gkam
1.8 / 5 (10) Feb 28, 2017
Meanwhile, . . .

"Radiation levels at Fukushima reactor puzzle nuclear experts"
http://www.asahi....042.html

"Search for melted nuclear fuel at Fukushima plant's No. 2 reactor faces obstacles"
http://mainichi.j.../011000c
WillieWard
5 / 5 (2) Feb 28, 2017
Meanwhile, . . .
Every 20 minutes, fossil fuels(backup for intermittent renewables) kill much more than carbon-free nuclear power in 70 years, and carbon-free nuclear energy is becoming ever safer through the time.

humy
4.7 / 5 (12) Feb 28, 2017
They are also more interesting-looking.
Interesting looking them slaughtering birds and bats in midair and displacing wildlife from their natural habitats.

WillieWard

Nothing compared to the carnage that would be done to birds and bats from burning fossil fuels and global warming that those wind turbines help to replace; you moronically completely miss the point.
humy
4.5 / 5 (8) Feb 28, 2017
Meanwhile, . . .
Every 20 minutes, fossil fuels(backup for intermittent renewables) kill much more than carbon-free nuclear power in 70 years, and carbon-free nuclear energy is becoming ever safer through the time.
WillieWard

Currently nuclear is not an economically viable option as it is by far the most expensive alternative to fossil fuels with wind tending to be currently the cheapest out of all of them.
+ the super grid and off-the-grid storage will solve the intermittency issue of renewables; a fact you moronically ignore.
Whydening Gyre
5 / 5 (5) Feb 28, 2017
They are also more interesting-looking.
Interesting looking them slaughtering birds and bats in midair and displacing wildlife from their natural habitats.

Actually...
These represent a smaller "footprint", making them easier to provide preventative protective measures...
WillieWard
2 / 5 (8) Feb 28, 2017
...burning fossil fuels and global warming that those wind turbines help to replace...
Intermittent renewables are not replacing fossil fuels and not helping to curb CO2 emissions, not in Germany, not in California, not in Vermont, and nowhere. Because it is needed fossil fuels for when wind is not blowing or sun is not shinning.
Greenpeace still uses diesel-burning ship and motorboats instead of wind turbines and solar panels to cross the oceans.
http://wpmedia.ne...1808.jpg
https://pbs.twimg...2JT7.jpg
WillieWard
1.9 / 5 (9) Feb 28, 2017
the super grid and off-the-grid storage will solve the intermittency issue of renewables
If it is so good, and economically viable, why isn't Greenpeace using it to power their ship and motorboats?
gkam
1 / 5 (6) Feb 28, 2017
Have some to sell?

No?

Oh.
NiCuCo
5 / 5 (9) Feb 28, 2017
the super grid and off-the-grid storage will solve the intermittency issue of renewables
If it is so good, and economically viable, why isn't Greenpeace using it to power their ship and motorboats?

Insufficient extension cords?
Da Schneib
5 / 5 (4) Feb 28, 2017
The research so far indicates that vertical axis wind turbines kill less birds. Whether that remains true will need to be seen. In addition, the studies so far have been on land, not at sea (and especially not near shore, where bird activity is high). The largest factor affecting lethality of wind turbines, particularly among more valued or rare birds (golden eagles, red tailed hawks, raptors generally) seems to revolve around (sorry, had to) access to food; the highest kill rates are in areas where land development to support the turbines has opened rodent habitat, attracting the raptors to a food source.

One thing that might help would be to make sure that the VAWTs are constructed without attractive sites for marine animals to populate.

Bird strikes are a major hazard at airports; wind turbine array designers take note. The methods used there are of great interest to civil engineers, I think.
Eikka
4 / 5 (4) Mar 01, 2017
All that speculation is moot because the economics isn't there for VAWT. Even in large groups, the swept area per unit is very small and the turbine is operating too close to the ground in the boundary layer where air movements are slowed by ground roughness.

All that translates to low power output per unit, and that goes in the opposite direction to the economy of scale: more things to build, more things to maintain, by a factor of 100x as the article points out.

a closely-spaced array of VAWTs can potentially generate up to 10 times more power per unit of land area than an array of widely-spaced HAWTs.


That's an apples-to-oranges comparison because of the different operating regimes. VAWTs operate at low wind-to-tip-speed ratios and achieve their peak efficiency and peak output at lower wind speeds, while HAWTs need higher winds to reach optimum output and can extract more energy out of higher wind speeds while the VAWTs do not.
Eikka
4 / 5 (4) Mar 01, 2017
See for reference: http://www.scielo...06-2.JPG

Low tip-speed-ratio means that the blades have to travel at or close to the wind speed, while high TSR means the turbine can turn much slower than the wind. That means it can operate up to higher wind speeds without spinning too fast for its construction.

And it just so happens the 3-bladed turbine has the highest efficiency out of the practical bunch. The Darreius type turbine starts spinning a little earlier but also cuts out or saturates at lower wind speeds, and knowing the V^3 relationship of power to speed it simply makes far less power and far less energy.

So at equal wind speed the VAWT array may output more at some constant wind speed, but the regular three-bladed HAWT makes more energy overall in the real world because it operates up to higher wind speeds.
Eikka
3.7 / 5 (3) Mar 01, 2017
So because of the above,

we think that the VAWTs can have blockage effects causing speedup around the turbines that helps downstream turbines.


That may not be practically so, especially at high winds when most of the energy is generated.

Besides, there's still the large scale limit of about 1 MW per square kilometer that doesn't depend on the turbine type, but is caused by the general slowing down of the air masses which cause winds to lift above and around the region where you're extracting wind energy.
humy
4 / 5 (8) Mar 01, 2017
...burning fossil fuels and global warming that those wind turbines help to replace...
Intermittent renewables are not replacing fossil fuels

WillieWard

Whether they currently are is irrelevant to the fact they can replace fossil fuels.

+ I am not a supporter of green peace. One doesn't need to be a political supporter of green peace to accept scientific fact as fact, moron.
Eikka
4 / 5 (4) Mar 01, 2017
Low tip-speed-ratio means that the blades have to travel at or close to the wind speed, while high TSR means the turbine can turn much slower than the wind. That means it can operate up to higher wind speeds without spinning too fast for its construction.


Correction: the TSR works in the opposite way. The blade travels faster than the wind. My memory failed me.

However the rest is correct as far as I can tell: Darreius and VAWT types in general reach their maximum output at lower wind speeds than the usual three-blade design. The reason why isn't readily apparent to me.

Whether they currently are is irrelevant to the fact they can replace fossil fuels.


How? With energy storage they might, but energy storage isn't available or is much too costly to implement. It seems to me that this isn't a question of the renewables themselves at all - it's everything else that either makes or breaks it.
Eikka
3.4 / 5 (5) Mar 01, 2017
One doesn't need to be a political supporter of green peace to accept scientific fact as fact, moron.


The point about greenpeace is that, as a figure of speech, even the greenies can't eat their own dog food. The people who are most ardently against everything and act like saints can't help but scoot around the planet in jet planes and diesel powered ships while shouting their agenda through a plastic megaphone made out of oil.

Plus, Greenpeace has never been about fact - it's always been a political organization and a self-serving money grab. Environment comes second to their social agenda, which is mostly anti-establishment, anti-capitalism. It's a grab-bag of misanthropists and cynical ex communists who see an opening for their brand of authoritarian tyranny with the environmental cause.

If the Greenpeace say the earth is round, you better bust out your theodolite and measure it again.
humy
5 / 5 (3) Mar 01, 2017


Whether they currently are is irrelevant to the fact they can replace fossil fuels.


How? With energy storage they might, but energy storage isn't available or is much too costly to implement. .

1, we already have some cost-effective albeit limited energy storage in the form of storage of water in hydroelectric dams thus proving your above assertion FALSE.

2, More cost effective energy storage using flow-battery technology (to replace current stationary batteries) using common chemical elements only and none toxic material only is being currently developed and it is just a matter of time before it becomes cheap enough to be economically viable.
If you don't believe me,

https://techxplor...eep.html

3, what about a supergrid? That alone even without energy storage has the potential of cost-effectively solve the problem. The only reason it hasn't happened yet is political and short termism.
humy
5 / 5 (2) Mar 01, 2017
Greenpeace has never been about fact - it's always been a political organization and a self-serving money grab. Environment comes second to their social agenda,

Eikka

Yes, I TOTALLY agree with that! And I said nothing to imply the contrary! This is why I said I am NOT a supporter of green peace.

The environmental movement has been hijack by a load of irrational fanatical loud-mouthed anti-industry anti-science lunatics that give environmentalism a bad repetition it doesn't deserve by proposing stupid lunatic policies, such as stopping all tree felling thus put an end to sustainable forestry, or banning GM crops even though GM can help the environment by reducing pesticide use etc.

However, nevertheless, scientific facts are STILL scientific the scientific facts and being against measures to stop/reduce man made global warming just because of some stupid irrational loonies say we should would make you no more rational and just as stupid as those loonies.
Pooua
3.4 / 5 (5) Mar 01, 2017
Currently nuclear is not an economically viable option as it is by far the most expensive alternative to fossil fuels with wind tending to be currently the cheapest out of all of them.
+ the super grid and off-the-grid storage will solve the intermittency issue of renewables


Currently, off-the-grid storage isn't ready for industrial-scale deployment, despite all the hopes and claims pinned to it; nor do we know if or when it ever will be. I don't believe it wise to base the national energy segment on vaporware.

Nuclear not only can be, but must be, a key component of our energy future. Wind is never going to replace all of our baseline capacity, even if, some day, we come up with this off-grid storage wonder that we've been promised for decades.
RealityCheck
3.3 / 5 (7) Mar 01, 2017
Hi Eikka, Willie, Pooua. :)

Consider:

The massive cost of subsidies given to establishing/facilitating Coal and Nuclear energy industries. The same subsidies given to Green energy alternative could have given us all the cheapest/safest energy alternative industries BY NOW if the politicians and crooked 'business men' running them for their own profiteering hadn't sabotaged all attempts to encourage (via similar subsidies/incentives etc by govts) development/implementation of transitional green energy systems while we upgraded/replaced our grid/storage systems/options to integrate/handle all green energy sources/production.

Not to mention what we have wasted on "fusion" energy research etc; which by itself would have supplied all the money needed for more feasible/immediate green energy for all!

So, guys, about time you started to blame those politicians and crooked businessmen, instead of being part of the problem THEY keep perpetuating for 'subsidized' PROFITEERING. :)
WillieWard
3 / 5 (4) Mar 01, 2017
off-the-grid storage will solve the intermittency issue of renewables
First battery 1749
No major commercial battery breakthrough since Li-phosphate 1996(two decades)
If climate change solutions involving intermittent renewables depend on off-the-grid storage solutions that don't exist, in what way are they solutions?
https://pbs.twimg...5BVh.jpg
https://pbs.twimg...A4Q1.jpg
https://pbs.twimg...Kv3G.jpg
RealityCheck
3.3 / 5 (6) Mar 01, 2017
Hi Willie. Thanks for your polite and on-topic response. Much appreciated. :)

As for your comment, it seems you missed the point I made. :)

Consider: If the same subsidies and supports/facilitation etc which were (and still are being) given to coal/nuclear/fusion projects/developments were also given to alternative green energy tech development/implementation, then we would be totally self-sufficient and totally backed-up in green energy TODAY. The delays caused by sabotage and lack of encouragement (due to politicians and the crooks running them) is why we are still having this discussion NOW.

As for your logic/example: Consider when the first coal-fired boiler and the nuclear reactor was first invented; and how not much has changed in the way coal-nuclear powered generation is still done using BOILED WATER....and requiring MORE WATER to condense/recycle the steam?

See what I mean, Willie? Your arguments for coal-nuclear-fusion only support wind/solar/battery more! :)
WillieWard
1 / 5 (1) Mar 03, 2017
With wind and solar, it is ever more impossible to curb CO2 emissions. Our only hope to stop climate change is carbon-free nuclear power.
"You Can't Have Offshore Wind Power Without Oil"
https://www.forbe...troleum/
"Dirty Secret Behind Wind Turbines, They Need Lots Of Oil"
"Just installing the foundation of a single offshore turbine can consume 18,857 barrels of marine fuel during construction, according to calculations published by Forbes Wednesday."
http://dailycalle...-of-oil/

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