&Cartridge; physics 14, 112

Simulations indicate that optimally placed barriers could increase the performance of wind farms by up to 10%.

L. Liu and RJAM Stevens [1]
The answer blows. A simulated six-row wind farm with wind protection (low walls in front of turbines). Dark blue stands for wind turbine lag; light blue stands for windbreak caster.

Inexpensive ways to generate more renewable energy are vital in the fight against climate change. New simulations suggest that windbreaks – barriers such as walls or rows of trees – can improve the power generation of wind farms by up to 10%. [1] . Previous work indicated that windscreens can help individual wind turbines, but are counterproductive for very large wind farms. The new work is the first simulation of a realistic wind farm with wind protection. The researchers involved hope that their work will increase the efficiency of real wind farms.

L. Liu and RJAM Stevens [1]
As above, dark blue stands for wind turbine wake and light blue stands for wind protection wake.

Worldwide, wind turbines currently generate 740 gigawatts of electricity – enough to supply New York City with electricity 70 times. But if fossil fuels are to be dwarfed, all renewable energy sources – including wind – need to generate much more electricity. One way to generate more energy is to make wind farms more efficient.

Researchers have improved the efficiency of wind farms by relocating the locations of the turbines to prevent each row of turbines from receiving the slowed and turbulent wake from the row immediately in front. Wind protection could potentially improve efficiency even further. In the direction of the wind of a windbreak, air below the height of the windbreak is slowed down, but the air above the top is accelerated. This acceleration effect is comparable to a liquid flowing through a funnel.

Simulations from 2017 showed that a windshield could help a single turbine by accelerating the air hitting the rotor blades, but that a windshield in front of each turbine in an infinitely large wind farm would reduce overall performance [2, 3] . The simulations showed that the wind acceleration only lasted a short distance, enough to help the turbine right behind the windbreak. But the slowed-down air can spread far in the direction of the wind in a wind farm and can become increasingly harmful if several wind protection eddies are combined. For an infinite wind farm, this cumulative wake effect cancels any benefit from accelerating the wind across any windbreak. However, no one had run a full simulation to test the value of wind protection for a finite, realistic wind farm.

Bob Jones / Windbreak Trees at Methwold Common / CC BY-SA 2.0 / Wikimedia Commons
Tree wall. Tree windscreens, like this one in the UK, have traditionally been used to protect plants and soil, but could also increase energy production from wind farms.

Luoqin Liu and Richard Stevens from the University of Twente in the Netherlands simulated a six-row deep wind farm with an identical windbreak in front of each turbine. They varied parameters such as the height and width of the windbreak and the distance between it and the turbine.

They found that the ideal windbreak is around 10% of the turbine height and around five times as wide as it is high. Shorter windshields had little effect, and larger ones created too large an area of ​​slow-moving air in their wake. At this optimal altitude with only six rows of turbines, the slow wake did not accumulate enough to negate the benefits of the windshields.

According to the results, the ideal wind protection for a 100 meter high turbine in a wind farm would be 10 meters high and 50 meters wide. “The easiest thing you can do is plant a lot of trees,” says Liu. Planting rows of trees to increase wind power by 10% would be both green and extremely inexpensive, he says.

L. Liu and RJAM Stevens [1]
Where the wind blows. Simulation of six rows of wind turbines in profile with colors indicating the degree of suppression of air speed, from zero deceleration (blue) to the most extreme deceleration (red). Slightly reduced wind speeds (light blue) at the lower edges of the turbine blades without a wind protection (above) are replaced by higher speeds (dark blue spots) with a wind protection of 12% of the turbine hub height (below). (The draft shield in front of each turbine in the picture below is a tiny black vertical line.)Where the wind blows. Simulation of six rows of wind turbines in profile with colors indicating the degree of suppression of air speed, from zero deceleration (blue) to the most extreme deceleration (red). Slightly reduced wind speeds (… show more

Although Liu and Stevens validated their simulation by comparing their data with existing field measurements of airflow over windshields, many questions remain unanswered. Their simulation did not take into account factors such as offset wind farm layouts, changes in wind direction or the effects of the rotating turbine blades on the turbine wake. “We don’t know whether we can really achieve this 10% if we build a real windbreak,” says Liu. “This is a new idea. Nobody has tried it yet. “

The new result makes other scientists think about practical implications. Azadeh Jafari, a fluid dynamics researcher at the University of Adelaide in Australia, points out that much of the improvement in power generation comes from the first row of turbines. “Maybe we can develop a strategy to address the [windbreaks] only in the front row instead of the whole field, ”she says.

“10% is a really big deal,” says Leonardo Chamorro, a mechanical engineer at the University of Illinois at Urbana-Champaign. “Everyone is surprised that wind turbines look like relatively old technology,” he says. “We know a lot, but there is a lot to do.”

–Dan Garisto

Dan Garisto is a freelance science writer based in New York.

References

  1. L. Liu and RJAM Stevens, “Improved Wind Farm Performance Through Wind Protection”, Phys. Rev. liquids6th, 074611 (2021).
  2. N. Tobin et al., “Fractional flow acceleration of porous windshields for improved wind turbine performance”, Boundary layer meteorol.163, 253 (2017).
  3. N. Tobin and L. Chamorro, “Windbreak Effects within Infinite Wind Parks”, Energies10, 1140 (2017).

areas of expertise

Energy ResearchFluid Dynamics

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