[yframe url=’http://www.youtube.com/watch?v=qNNo5Qr8LWA’]Bad news for wind farms: the earth may have far less wind capacity than previously thought, according to a new study from professors at Harvard University and the University of North Carolina. Up to this point, most limits to wind power have centered on our inability to efficiently harness it, permit it, and site it. But new research suggests geophysical limits will also hamper the fledgling energy source.The chief problem is “wind shadows.” These are created when the drag from wind turbine blades slows down the air moving past them. This problem has been understood for years. Wind farm planners take it into account when placing turbines, spacing them far enough apart so that one turbine’s blades don’t affect the wind “supply” of another’s.But just as turbines slow down the air immediately behind them, whole wind farms create shadows that affect local and even regional weather patterns. Current estimates of global wind power capacity don’t take this effect into account. If they did, researchers say, they would be forced to trim their estimates of peak production levels from 2-4 watts per square meter down to a maximum of just one watt per square meter at large wind farms. In other words, our planet’s wind energy capacity has been overestimated by as much as two to four times.This doesn’t mean that wind energy can’t be an important component of the world’s energy mix in the future, but it should inform policymakers looking to plan for the future.