Study: Wind Farm Generative Capacity May Be Limited

Wind power and wind farms may not be capable of producing as much energy as previously believed, according to a paper co-authored by Harvard scientist David W. Keith.

Keith, a professor at the John F. Kennedy School of Government and the School of Engineering and Applied Sciences, co-published the paper on Feb. 25 in the online scientific journal Environmental Research Letters with Amanda S. Adams, an assistant professor at the University of North Carolina at Charlotte.

Their study examined the long-range effects of one wind farm on another. The spacing between turbines is critical to each of their individual functioning, because a turbine placed directly behind another turbine cannot spin at full capacity and is therefore less efficient and able to put out less energy. This phenomenon is caused by the fact that in order to operate and move its blades, a wind turbine takes mechanical energy out of the wind passing through it. As a result, the speed of wind that has already passed through another turbine is lower when it hits the next in a series of the devices.

Therefore, when a wind farm becomes large enough, according to the study, it can have a larger impact on the energy-producing capacity of surrounding wind farms. Due to these diminishing returns, Keith said future efforts to scale up the amount of wind power produced on earth will result in each new wind farm producing less power relative to its land area than previously expected.

Keith said that past investigations into the impact of one turbine on another did not take into account large-scale decreases in wind speeds that arise from entire wind farms essentially removing energy from the wind.

“The old-style idea was that you just add it up,” Keith said. “You calculated the wind at the turbines around the world, and you added up all those things as if they work independently.”

But even with diminishing power output, covering vast areas of land with turbines could potentially provide for power demands in the U.S., Keith said. However, Keith warned, the large number of turbines could come with other costs and consequences.

Keith explained that although an individual wind turbine may be efficient, turbines in large numbers are both expensive to build and relatively inefficient when functioning collectively.

If advances cannot make turbines more cost-efficient, Keith said, a significant increase in the amount of power produced by wind will not be financially sensible.

Beyond monetary concerns, the paper also emphasizes that the implementation of wind power on a large scale can have a significant impact on the local environment. Keith said these effects will become significant and visible “well before” wind power supplies a third of U.S. primary energy

While Keith said he believes wind power is a good alternative to coal or petroleum, expanding wind power to the scale of either energy resource would result in changing temperatures on Earth, which could impact a myriad of issues like crop growth. Land use also becomes a serious issue as wind farms become larger leading to the a need to build access roads to the turbines, Keith said.

Keith said that although he would not totally discourage further research into wind power, he thinks people should put less effort into its development relative to other alternative energies, such as solar and nuclear power, which have more potential to offer a sustainable solution to energy demands.

“We have to think analytically with numbers about what the consequences are of scaling up...and realize there are some [energy sources] we wouldn’t want to scale even if we could,” Keith said.

Keith said he thinks policymakers should take into account existing research when allocating funds for energy development in the future.

“This is a game of moral responsibility and political decision-making,” Keith said. “This is not some kind of passive guess about what happens. We’re part of the guess. We need to make political decisions about what we want to have happen, not guess.”