Stanford Study Shows Realigned Wind Turbines Can Increase Wind Farm Production

July 9, 2019 by Steve Hanley

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People who are racing or sailing know the wind's aerodynamics and turbulence. Racing cars leave behind eddies of disturbed air, which slows cars down. Sailboats have similar turbulent eddies, slowing the boats that follow. Stanford researchers examined the adverse effects of wind turbines on the efficiency of other turbines in the region and found that turbulence can reduce the efficiency of wind turbines by 40% or more. Their research was published this month in the journal Proceedings of the National Academy of Sciences.

During an experiment conducted at a wind farm in Alberta, Canada, researchers repositioned wind turbines so that the turbulent air they created has less impact on other wind turbines. of the region, a process that they call the wake direction. The research is preliminary but encouraging, particularly at a time when the variability of renewable energy sources argues in favor of maintaining Peaker plants.

"To meet global targets for renewable energy production, we need to find ways to generate much more energy from existing wind farms," ​​said John Dabiri, a Stanford University professor, lead author. of the document. "The focus has traditionally been on the performance of individual wind turbines in a wind farm, but we need to start thinking about the farm as a whole, not just the sum of its parts."

Renewable Energy Magazine reports that turbine wakes can reduce wind generator efficiency by more than 40%. Previously, researchers used computer simulations to show that misalignment of turbines due to prevailing winds could increase turbine production downstream.

First, the Stanford group has developed a faster way to calculate the optimal misalignment angles for turbines. They then tested their calculations in collaboration with TransAlta Renewables, the operator of the Alberta wind farm. The total power of the farm increased by 47% in light wind, depending on the angle of the wind turbines, and 7 to 13% in the average wind. The waking direction also reduced the ups and downs of the current, which is normally a challenge for wind energy.

"Thanks to the wake management, the front wind turbine produced less power than expected," says Michael Howland, doctoral candidate, lead author of the study. "But we found that because of the decrease in wake effects, downstream turbines generated a lot more power."

The improvement of the power observed at low wind speed was particularly important because the turbines generally stopped running at a minimum speed, which completely reduced the production and forced the network operators to use more power. the emergency energy. In addition, turbulence caused by wakes can make wind farm production irregular minute by minute, making it difficult to match supply and demand for very short-term network operators. In the study, wake management reduced the very short-term variability in energy production by 72%.

To calculate the best misalignment angles for this study, the researchers developed a new model based on the wind farm's historical data: "The design of wind farms is usually a very complex task in data and calculation," said the professor. Sanjiva Lele. "Instead, we have established simplified mathematical representations that have not only worked but also reduced the computational load by at least two orders of magnitude."

This faster calculation could help wind farm operators make extensive use of wake management. "Our model is essentially plug-and-play because it can use site-specific data on wind farm performance," said Howland. "Different farm locations will be able to use the model and continuously adjust the angles of their turbines according to the wind conditions."

The next step, Dabiri said, will be field testing for a whole year. "If we can get to the point of being able to deploy this strategy on a large scale for long periods of time, we can potentially optimize aerodynamics, energy production and even land use for wind farms. all over."

Keywords: Stanford University, Wind Turbine Wake Management, Wind Turbines