New modeling study shows a “slowdown” effect if too many turbines are clumped together
FRISCO — Wind turbine installations could some day reach a point of diminishing returns if they get too big, according to a new study that evaluated the effects of large wind farms on atmospheric flow and its implications for how much renewable energy the turbines can generate.
The researchers at the University of Kansas did their study in the context of the renewable energy boom. Wind energy accounted for 3.3 percent of electricity generation in the United States in 2011. The study was aimed at learning what happens to the wind when a larger number of wind turbines removes more and more of the energy of atmospheric motion.
“Wind turbines generate electricity by removing energy from the wind, so a larger number of wind turbines should result in a slowdown of the winds in the lower atmosphere,”said David Mechem, with KU’s Department of Geography.
The researchers quantified this phenomenon in numerical simulations by applying a sophisticated model normally used for weather forecasting to one of the windiest regions of the United States.
The team found that a slowdown effect triggered by wind turbines is substantial for large wind farms and results in proportionally less renewable energy generated for each turbine versus the energy that would be generated from an isolated wind turbine.
The researchers explained that no current or planned wind farm approaches the size or concentration that would cause a slowdown effect, but their results suggest the phenomenon tied to large wind farms needs to be accounted for in future planning of wind energy.
“When just a few wind turbines are installed, each additional turbine results in a similar increase in electricity generated, as you might expect,” said KU’s Nate Brunsell.
However, when a substantial number of turbines are installed over a small area, the amount of electricity generated is no longer governed by simple multiplication, according to the researchers.
“Instead, because the turbines extract energy from the wind, additional turbines will each generate less and less electricity,” Mechem said.
The team’s simulations estimate this slowdown effect results in a practical upper limit of 1 megawatt per square kilometer that can be generated — far less than previous estimates not accounting for the effect.
Current wind farms are operating well below this generation limit, but the authors found that this slowdown effect needs to be accounted for, particularly when comparing different sources of renewable energy.
The study was published online in the scientific journal Proceedings of the National Academy of Sciences on Aug. 24.