Is The Sky The Limit For Wind Power?
Wind power is growing faster than ever — almost half of the new sources of electricity added to the U.S. power grid last year were wind farms.
But is the sky the limit? Several scientists now say it’s actually possible to have so many turbines that they start to lose power. They steal each other’s wind.
Sailboat captains experience a similar phenomenon; they call it “dirty air.” If you’re sailing directly downwind of another sailboat, you’ll slow down. That’s because the lead boat creates a turbulent vortex of air behind it as the wind spills off its sails. As sailors know, “dirty air” means less power.
The blades on wind turbines make dirty air too, so engineers space the machines far apart. But wind developers want to bring the total number of turbines in the U.S. to more than 100,000, up from about 45,000 today. Would that spread the turbulent air far and wide?
Harvard physicist David Keith says that’s possible. “[With] very large wind farms,” he says, “we can now see long footprints that extend, in some cases, tens of kilometers downstream, where you have slower-moving wind.”
Keith is one of several scientists who have designed computer simulations to see what might happen at huge wind farms. “If we’re going to scale wind power up to supply a significant fraction of the global energy demand — say 10 percent of global energy demand as we get towards midcentury — then these effects begin to matter,” he says. “Exactly how much they matter we still don’t know.”
The answer has become a kind of puzzle for atmospheric scientists. Just what, they ask, is the “saturation point” for wind power? That is, when is the wind so dirty that there’s no point in building one more turbine?
So far, that point is hypothetical. To get to saturation, you’d need huge wind farms –bigger than any that exist now — with thousands of square miles packed with turbines. For the 45,000 big turbines now spread around in clusters throughout the U.S., that’s not a problem.
Atmospheric scientist Mark Jacobson at Stanford University has done calculations that suggest you’d have to get up into the many millions of turbines before you’d lose a serious amount of wind. And people are thinking about how to get around the problem.
“We found that by spreading out the wind farms themselves,” Jacobson says, “you reduce this impact of having low energy when you just have one wind farm with lots of turbines.”