The Sky Is the Limit for Wind Power

The amount of power to be reaped from tapping low- and high-altitude winds dwarfs global demand

By David Biello

WIND POWER: The world's winds contain more than enough energy to power human civilization. Image: ? David Biello

Wind turbines on land and offshore could readily provide more than four times the power that the world as a whole currently uses. Throw in kites or robot aircraft generating electricity from sky-high winds and the world could physically extract roughly 100 times more power than presently employed?and the climatic consequences remain minimal.

Two new computer-model analyses suggest there are few limits to the wind's potential. Although "there are physical limits to the amount of power that can be harvested from winds, these limits are well above total global energy demand," explains climate-modeler Kate Marvel of Lawrence Livermore National Laboratory, who led the analysis published September 9 in Nature Climate Change. (Scientific American is part of Nature Publishing Group.) Current global demand is roughly 18 terawatts. (A terawatt is one trillion watts.)

Given the desire to reduce greenhouse gas emissions from electric generation, a growing number of wind farms are cropping up from the U.S. to China?more than 239 gigawatts worth of wind turbines have been installed globally. But the ultimate limits of wind power's potential contribution remained unclear. One complication, for example, is that any effort to harvest wind power ends up having an impact on the wind itself, reducing its speed?as well as influencing both local weather and global climate.

Using a global meteorological and sunlight-chemistry computer model paired with power generation information from turbine manufacturers, environmental scientists Cristina Archer of the University of Delaware and Mark Jacobson?of Stanford University analyzed when wind turbines might reach a saturation point?the point at which the addition of more turbines would reduce the amount of power generated, rather than increase it. At 100 meters up?roughly the hub height of a modern large-scale wind turbine on land?that saturation point would allow more than 250 terawatts of power to be generated, according to the results published online in Proceedings of the National Academy of Sciences on September 10. "We calculated how much electrical energy can be generated from the atmosphere," Archer explains, noting that four million turbines spread around the globe could easily and sustainably produce 7.5 terawatts of power, or nearly half of all power used today.

For their part, Marvel and her colleagues examined the geophysical limits of wind power, or how much energy can be extracted from global winds without major impacts. Surface winds below 395 meters, which ultimately dissipate anyway, could provide at least 400 terawatts of power, whereas those at higher altitudes could offer more than 1,800 terawatts based on atmospheric physics.

The researchers then used a computer model to simulate the global climate over a century to find out what impact such power extraction might have. If humans could figure out how to extract all that power, global temperatures could rise by as much as one degree Celsius and precipitation decreased by roughly 10 percent. Of course, that's more than 100 times more energy than presently consumed by the entirety of human civilization, suggesting that the actual impacts of wind power would be far smaller. "At the scale of civilization, the climate consequences of widely distributed wind turbines are negligible," says climate-modeler Ken Caldeira of Carnegie Institution's Department of Ecology at Stanford, a co-author with Marvel.

Source: http://rss.sciam.com/click.phdo?i=8dbc37743996d69570b84fd1dbaeeab3

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