Mechanical engineers develop ways to improve windfarm productivity

October 4, 2018 by Sonia Fernandez, University of California - Santa Barbara
mechanical engineer develops ways to improve windfarm productivity
Fog at an offshore windfarm shows the formation of wind shadows between wind turbines. Credit: VATTENFALL

You've probably seen them, perhaps on long roadtrips: wind turbines with enormous, hypnotic rolling blades, harnessing the clean power of wind for conversion into electric energy. What you may not know is that for the explosion in the number of wind turbines in use as we embrace cleaner sources of energy, these wind farms are quite possibly not as productive as they could be.

"We've been designing turbines for use by themselves, but we almost never use them by themselves anymore," said UC Santa Barbara mechanical engineering professor Paolo Luzzatto-Fegiz, whose specialty lies in fluid mechanics. Historically, he said, were used individually or in small groups, but as the world moves toward greener technologies, they are now found in groups of hundreds or thousands.

The problem with these large installations is that each machine, which has been designed to extract as much energy as possible from oncoming , may not "play well" with the others, Luzzatto-Fegiz explained. Depending on how the turbines are situated relative to each other and to the prevailing wind, those not directly in the path of the wind could be left to extract energy from significantly depleted airflow.

"These turbines are now very good at extracting power from wind, but they also form these very big wind shadows," said Luzzatto-Fegiz, who is the lead author of "Entrainment models for fully-developed : Effects of atmospheric stability and an ideal limit for wind farm performance," published in the American Physical Society journal Physical Review Fluids. Similar to how structures can attenuate the flow of light from one side to another, wind power also is lessened as it flows from the front of the to its rear. The result is that not all turbines in a wind farm are living up to their potential.

"So, you can see that it's not a matter of packing more turbines on your piece of land, because at some point you hit these diminishing returns," he said. "There's a point where if you keep adding turbines the amount of power you get becomes less."

However, according to Luzzatto-Fegiz and co-author Colm-cille P. Caulfield, a professor at the University of Cambridge in the U.K., there are ways to get around this issue of diminishing wind returns. And, they said, these enhancements could result in orders-of-magnitude improvements in the energy production of wind farms.

The main goal, according to the researchers, is to give all turbines access to high-velocity airflow, from which they can extract a greater amount of energy. Since the wind above the farm is much faster than between the turbines, mixing the airflow in the wake of the turbines with the air above could be the key to getting more bang for your wind turbine buck.

"If you could somehow invent a gadget that for each of these turbines causes these wakes to mix very quickly, you can potentially have these huge improvements," Luzzatto-Fegiz said.

Yet another potential solution is a relatively new version of the wind turbine, in which the blades rotate on a vertical axis—like eggbeater blades—as opposed to the traditional horizontal axis.

"These don't perform as well ordinarily by themselves, but it's significant that they essentially can cause much stronger mixing in their wakes," he said, "and people have shown that if you put them in an arrangement where they spin in opposite directions to each other they can cause very nice mixing."

The models developed by the researchers could lead to better-performing wind farms, which in some cases may not require as many turbines as previously thought, thereby reducing potential costs. The models also could result in custom solutions that involve the sites' specific terrain, and local weather patterns.

"We're really excited that we can model all that very accurately," said Luzzatto-Fegiz.

Explore further: Localized wind power blowing more near homes, farms and factories

More information: Paolo Luzzatto-Fegiz et al, Entrainment model for fully-developed wind farms: Effects of atmospheric stability and an ideal limit for wind farm performance, Physical Review Fluids (2018). DOI: 10.1103/PhysRevFluids.3.093802

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13 comments

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WillieWard
1.6 / 5 (7) Oct 04, 2018
"Batteries not included"
"Weather-dependent, part-time and highly variable wind and solar must be paired in a system with fossil fuel generation. They are not green or as cheap as advertised."
https://principia...olution/
"Renewables are like an employee that doesn't always come to work and when he does he works only for a few hours."
carbon_unit
4.2 / 5 (5) Oct 04, 2018
Willie: Batteries not always required. Batteries available and getting better all the time!

Interesting that the vertical designs are making a comeback. They seem simpler, most designs don't care about wind direction and have the generating equipment on the ground instead of suspended in the air.

The linked study seems to show a 40% loss of power for downwind turbines in a configuration/conditions like the photo. (Nature provides visualization of airflow!) Look carefully and you can see the other turbines in the wake of the lead turbines. A way around this loss will be very good.
howhot3
1 / 5 (2) Oct 04, 2018
"Renewables to a Republican operative are like an employee that flips off the company with the double finger when he works and moons them when he leaves."

" piece of crap websites that promote oil over solar and wind are pretty much deserving of a double flip off."

" solar and wind are basically free energy resources, Oil gas and coal are not free, super expensive, pretty toxic, and the primary cause of global warming."

" I'm holding up 6 fingers can you read the two fingers between the lines?"
WillieWard
1.5 / 5 (8) Oct 04, 2018
"Large-scale wind power needs more land, causes more climatic impact than previously thought" - Oct 4,2018
https://techxplor...sly.html
Wind/solar produce more ecological impacts than energy.

Batteries not always required.
"Solar/Wind = 3 x Gas"
Thorium Boy
2.4 / 5 (7) Oct 05, 2018
The best way to improve a wind installation to produce a lot more power in a given area of land is to install a gas or nuclear plant.
antialias_physorg
3.7 / 5 (3) Oct 05, 2018
double post
antialias_physorg
4.3 / 5 (6) Oct 05, 2018
Interesting that the vertical designs are making a comeback

Issue with vertical designs is that they aren't as tall as the regular ones. Height greatly influences how consistent energy production is.
There's also the mechanical aspect. The vertical ones have to contend with unfavorable loading on their bearings - making them less hardy than the old style.
rrwillsj
not rated yet Oct 05, 2018
well a_p, that sounded to me like a challenge? Now some bright boys and girls need to dive in and make the solutions to the problems a reality. Could be some lucrative business opportunities ahead.

WillieWard
1.8 / 5 (5) Oct 05, 2018
Wind/solar produce more ecological impacts than energy.
"Harvard researchers find that the transition to wind or solar power in the U.S. would require 5 to 20 times more land than previously thought, &, if such large-scale wind farms were built, would warm U.S surface temperatures 0.24 degrees Celsius."
"The down side to wind power" - Oct 4,2018
https://news.harv...wn-side/
"Enough turbines to generate all of America's power would warm the U.S. by 0.24 degrees Celsius"
https://www.scien...-climate
"Harvard: Wind power will create significant warming of 0.24C, plus eat up 5 to 20x more land than thought"
https://wattsupwi...thought/
howhot3
4.2 / 5 (5) Oct 05, 2018
Another series of lay-mo claims by @WarmWilly " if such large-scale wind farms were built, would warm U.S surface temperatures 0.24 degrees Celsius". Well compared to the 7 degrees globally that the Trump administration predicts with continued oil and gas, that sounds like small potatoes for wind and solar!

@WarmWilly also repeats; " Wind power will create significant warming of 0.24C". And the alternative is what? Assuming 0.24C is not some bullshit made up crap, who cares when compared to the 2-4C globally. Basically 0.24C compared to extinction? Your choice.

tekram
5 / 5 (5) Oct 06, 2018
What many claimed to be localized 0.24 °C warming of wind farms is just that - it is localized and not global. There is also cooling effect of nearly equal magnitude behind the wind farm.

Over time, the simulated wind turbines reproduced the satellite observed local warming effect within about one tenth of a degree (.20 to .26 °C on average). However, they also produced a downwind cooling effect (-0.2 °C on average) in the vicinity behind the wind farm region at night. Something that was not found by previous studies.

More information: Geng Xia et al. Simulating Impacts of Real-World Wind Farms on Land Surface Temperature Using the WRF Model: Validation with Observations, Monthly Weather Review (2017). DOI: 10.1175/MWR-D-16-0401.1
WillieWard
2 / 5 (4) Oct 07, 2018
... predicts with continued oil and gas, that sounds like small potatoes for wind and solar!
Notice: it's cheaper and more ecologically friendly to build a coal/gas-fired power plant, because a wind/solar farm(bird-chopper/landscape-destroyer) will require anyway a coal/gas-fired backup plant to compensate intermittencies.
https://pbs.twimg...1fTH.jpg
wind/solar = 20% wind/solar + 80% coal/oil/gas,
aside the fossil fuels used to manufacture/mine/transport/install/maintain/repair the windmills and solar panels.
Wind/solar aren't alternative to fossil fuels.
If Climate Change is a serious issue, carbon-free nuclear power is the only way to go.
carbon_unit
3 / 5 (2) Oct 08, 2018
The local surface warming wind turbines cause is not additional heat in the environment as is warning caused by greenhouse gasses. It is due to warmer air above the surface being brought down to the surface by the churning cause by the turbine. Heat is simply being moved around. The effect is strongest at night. If whatever activities are happening on the ground are not disturbed by this slight increase or perhaps benefit from it (crops protected from frost?), then no problem. There is no effect on a global scale. The land use around turbines should not be a big issue either because you can use the land around a wind farm for, well, farming! The turbines have a minimal footprint.

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