by Marcus Y. Woo, Engineering & Science. An article relevant to GSS Energy Use chapter 10. Excerpt: …John Dabiri… was studying how air flows around solid structures… trying to make wind turbines work efficiently amid the swirling gusts near buildings and skyscrapers, providing a source of renewable energy for cities. But as he played with the equations, he realized that they looked a lot like the ones that govern the flow of water through a school of swimming fish.
Once he saw the connection between fish schools and wind turbines, it seemed natural to put them together. … if every currently existing wind turbine were churning out as much power as possible, the United States would have the capacity to generate some 40 billion watts of wind power, which would account for 2 percent of the nation’s electricity. The maximum potential capacity of land-based wind power in the continental United States is estimated to be about 10 trillion watts, or terawatts (TW). Building wind farms on every suitable patch of land in the world could provide 75 to 100 TW. Considering that global power consumption was about 15 TW in 2008, wind could—in principle—power the entire planet.
…But one big problem with wind power is that conventional turbines—the ones that resemble huge propellers— need a lot of space. …In theory, wind turbines can convert 60 percent of wind energy into electricity. In practice, the best are already at 50 percent.
…Dabiri’s fish-inspired wind farms use the lesser-known vertical-axis turbine, which looks a little like an eggbeater jutting out from the ground. When fish swim, they leave a horizontal row of regularly spaced vortices in their wakes; what would happen, he wondered, if he placed his downwind turbines in those vortices, and let them spin the turbines?
…Individually, a vertical-axis turbine is less efficient than its monolithic cousin. But ...Horizontal-axis turbines only capture the wind that blows through the circles swept by their blades, allowing precious energy to escape through the gaps between them. Vertical axis turbines ... can be bunched together until they’re almost touching, harnessing the energy of almost all the air that blows by.
…Vertical-axis turbines have other advantages. They’re safer for birds. And instead of being 100-meter tall structures … vertical-axis turbines are around 10 meters tall. Because they’re quieter and smaller, they can be distributed more widely and can be built closer to population centers.... Read the full article: http://climate.nasa.gov/EnergyInnovations/index.cfm?FuseAction=ShowEnergy&EiID=555
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