LARAMIE — Worldwide, the low efficiency of wind farms is a mystery that one UW professor is working to solve with new models and access to the NCAR-Wyoming supercomputer.
Stefan Heinz, a professor in the University of Wyoming Department of Mathematics who has studied turbulence and combustion for more than 20 years, says he can perform computer simulations of wind farms that are more accurate and less expensive than existing models.
"Right now, no one really understands how a wind farm works. No one knows how one turbine affects the efficiency of another," said Heinz, who conducts research at UW's School of Energy Resources' Wind Energy Research Center. "We need computer simulations that are accurate and as inexpensive as possible to help businesses that build wind farms or turbines."
The basic problem of calculating wind-turbine efficiency via computer simulations is that the grid applied in numerical simulations has to use a very small cell size and cover a large domain, making good simulations expensive, Heinz said.
Theoretically, he said, a wind farm's performance should exceed the production of the same number of isolated wind turbines. However, in reality, the overall efficiency of wind farms is below this value because the first turbine disturbs the energy efficiency of the next turbine, and so on. In other words, two plus two does not necessarily equal four in wind-farm reality.
"With a wind farm, you have one turbine after another. Each turbine rotates air and creates a wake behind it," Heinz said. "This air will heavily affect the next turbine. Efficiency of wind farms is relatively low."
Due to the wakes, the efficiency of wind turbines is reduced by 20-50 percent compared to turbines in isolation, according to generally accepted research in the field.
Heinz said that turbine-performance reduction could possibly be due to one or a combination of factors, including: the distance between wind turbines, the height of the turbines, variations in topography between the turbines and rotor size and shape. Heinz plans to study an enclosed wind turbine that spins horizontally, much like a weather vane, to see whether such a model would be more efficient.
With computer simulations, such variables can be changed to determine the impact on wind turbine performance and provide more clues to which wind farm arrangement is most efficient, Heinz said. As a result, it would be theoretically possible for a wind farm to operate with a higher efficiency than the same number of isolated wind turbines, he said.
"We want to not only change the (wind turbine) interaction, but also to understand the interactions," he said.
And this winter, Heinz will have access to the NCAR-Wyoming supercomputer to create more accurate simulations, improving potential efficiency in future wind farms. He said even an increase of 1 percent efficiency "will have a significant impact on the energy supply."
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