Should the Wind Turbine Industry Head for the Hills?

At dusk outside Limon, an isolated interstate interchange on Colorado’s vast eastern frontier, a string of active wind turbines lines the southwest horizon — their red aviation warning lights almost keeping time with their rotating blades. And more are on the way; the local hotels are packed with summer wind farm construction workers pulling three shifts a day.

In fact, such high desert landscapes are an obvious choice for wind power technology — but what about the mountains and hillsides that never seem to top the wind energy list?

These steeper gradient sites are getting a second look.  Hui Hu, an aerospace engineer at Iowa State University, and colleagues have been studying how hillside gradients and hilly terrains impact wind energy models for wind farms.  Hu argues that current models are based on wind energy efficiencies for turbines on a flat terrain, without taking into account the dynamics of turbines on hillsides.

Until now, there’s been a data gap when engineers consider the effects of atmospheric winds on uneven terrain.  But the engineers at Iowa State used scale model mini-turbines in a large on-campus wind tunnel to study the effects of hilly terrain and turbine placement on power production.

“Tools for predicting how existing wind turbine farms will work aren’t well developed, so people resort to rules of thumb,” said Richard Wlezien, Iowa State’s Chair of Aerospace Engineering.  “But you can’t just look at an array of turbines and say this is a good or bad way to align them.”

Hu’s argument is that by modeling turbines on hillsides we can get a more accurate picture of energy potential on hilly or mountainous terrain, since wind farm designs are still based on flat terrains.

Hu’s group is studying how the steep [20 to 40 degree] gradients of a hill impact the turbine efficiency.  The results show that turbines on hilly terrain experience higher wind loads than their flat terrain counterparts.

As a result, wind making its way over hilly terrain recovers its power potential more quickly as it moves from turbine to turbine.  Hu reports that his results show that on hillsides, turbine rows can be more closely spaced than previously thought.

“That means for the same acre of land you can put more wind turbines, and thus [harvest] more energy, out of a given project,” said Hu.

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