February 25, 2013
Keeping Realistic Expectations About Wind Energy
Michael Harper for redOrbit.com — Your Universe Online
According to new research from the Harvard School of Engineering and Applied Sciences, the notion that wind energy presents an unending supply of power might be a bit misleading. While there may be no end to breezes and gusts, the way we harness them could be counterproductive, according to applied physicist David Keith. His latest research, which applies mesoscale atmospheric modeling, finds large-scale wind farms will not be as effective as previously thought. His conclusions have now been published in the journal Environmental Research Letters.
The issue lies in the byproduct of these wind turbines, an effect called a “wind shadow.” As the turbines spin, the drag created by the turbines slows the speed of the wind. A properly executed wind farm of appropriate size accounts for wind shadow, spacing the turbines far enough apart. Keith warns, however, as these wind farms begin to grow and grow closer to one another, they´ll begin to interact with one another, affecting the regional-scale wind patterns.
According to his research, “very large” wind farm installations of 62 or more square miles apiece might only be able to generate less than one kilowatt per square mile. There had been previous estimates that did not take wind shadow into effect. These estimates held these large wind farms would be able to generate as much as seven kilowatts per square mile.
Amanda Adams, a former postdoctoral fellow with Keith and currently a professor of geography and earth sciences at the University of North Carolina at Charlotte helped Keith write this report. In a press statement, Adams says our trying to capture the wind is in it´s very nature altering how much of this wind is available to us.
“One of the inherent challenges of wind energy is that as soon as you start to develop wind farms and harvest the resource, you change the resource, making it difficult to assess what´s really available,” said Adams.
It´s important to get an accurate estimation as to how much energy we can expect from wind, according to Keith. Without a realistic expectation, energy experts won´t know how much to realistically expect from other sources, such as solar or hydropower.
“If wind power´s going to make a contribution to global energy requirements that´s serious, 10 or 20 percent or more, then it really has to contribute on the scale of terawatts in the next half-century or less,” says Keith.
“Our findings don´t mean that we shouldn´t pursue wind power–wind is much better for the environment than conventional coal–but these geophysical limits may be meaningful if we really want to scale wind power up to supply a third, let´s say, of our primary energy.”
Keith says his research isn´t meant to discourage looking to wind as a renewable energy source. Instead, he hopes it will give us realistic expectations about wind as a source of energy.
“The real punch line,” he adds, “is that if you can´t get much more than half a watt out, and you accept that you can´t put them everywhere, then you may start to reach a limit that matters.”