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Why don't Indiana wind farms operate on windy days?
December 24, 2009

Dear Cecil:

I drove to Indianapolis Monday, December 7 to attend the baseball winter meetings. As I drove south on I-65 through the beautiful cornfields of central Indiana, somewhere near Rensselaer, on the east side of the interstate, I encountered a huge wind farm, with dozens and dozens of huge wind turbines stretched out as far as the eye could see. (Made me think of a 50s sci fi movie.) They were all in motion at a moderate pace, as there was approximately a 10-mile-an-hour wind. No big deal. But after two days of watching 30 general managers try to make deals on cocktail napkins while avoiding the press in the hotel bar, it was time to drive back to Chicago. As you may recall, Wednesday, December 9, was the snowstorm/blizzard across middle America, with winds howling from Wyoming to the eastern seaboard. So, while driving back home north on I-65 around noon with the winds gusting at over 50 MPH, I was looking forward to observing the wind turbines spinning around madly like my electric meter in the summer with the AC running full out. But when I drove past the "farm," guess what? THE WIND TURBINES WERE ALL TURNED OFF, DEAD STILL, SLEEPING AT THE SWITCH, HIBERNATING, LOCKED DOWN AND STOPPED COLD. All I could think of was that this had to be the biggest lost opportunity of all time due to some goofball accidentally throwing the wrong switch at windmill command. Or could it be that these big turbines can't handle it when the wind comes whipping off the plains?

— Mike Murphy, Chicago

Cecil replies:

We'll get to your question in a second, Murph. But first we'd better tackle one sure to have some Straight Dope readers scratching their heads: since when is there a big wind farm visible from I-65 near Rensselaer?

Since about five weeks ago, that's when. (Other facilities have been operating for longer times elsewhere in the state.) I'm guessing you saw the wind farm operated by Horizon Wind Energy at Brookston, Indiana, roughly 25 miles south of  Rensselaer, which was dedicated November 19. This impressive installation has 121 wind turbines and can generate 200 megawatts, enough to power 60,000 homes — and that's just phase 1. Phases 2 through 4, expected to be completed by October 2010, will push the output to 500 megawatts. The long-term plan, which depends on boosting transmission capacity, is for 660 turbines generating 1,000 megawatts spread over 100,000 acres.

If you're thinking all this alternative energy seems uncharacteristically progressive for a place like Indiana, you need to get with the times. Wind power has become a big business, and the wind doesn't blow only in blue states. A major center of wind power generation is west Texas; Horizon's headquarters is in Houston. Most of the company's 21 wind farms are in central U.S. states ranging from Oklahoma to Minnesota. While the breeze in Indiana is less formidable than some places, it's reasonably steady, and the I-65 location has the advantage of being midway between two major centers of electricity consumption, Indianapolis and us.

On to the heart of the matter: why lock down the turbines when the breeze is really blowing and you could pump out some serious juice? You've already guessed the reason: for fear the big windmills will rip themselves apart if the gale gets too fierce. The danger isn't strictly theoretical — check out the Danish wind turbine accident on YouTube. Horizon's turbines start generating electricity when the wind reaches 6 to 9 MPH and reach maximum output at 22-25 MPH. They automatically shut down above 42-44 MPH, known in the business as the cutout speed. When wind speed drops below that level, operation automatically resumes.

To restless minds such as ours, Murph, this doubtless seems a regrettable waste. It's all very well to have your turbines rotating in a desultory manner in some 10-MPH zephyr, but we've all watched enough Discovery Channel specials to know nature's real power lies in storms. Isn't there some way to harness those?

I put the question to Bill Whitlock, director of development for Horizon's Great Lakes region. His answer: storms with high winds like the one we had earlier this month are brief and relatively rare; you need to design the system for average conditions. Despite shutting down when the winds are particularly fearsome, midwestern wind farms typically generate 30-35 percent of theoretical maximum output. Texas wind farms, for comparison, generate 40-45 percent.

Then again, conventional power plants commonly operate at 80 to 90 percent of capacity, so the wind industry has a distance to go. One goal of wind turbine research is to increase the cutout speed, and once you get past that you've still got the problem of where and how to store the energy a storm would generate. Still, after two hours digging out the driveway, it'd be nice to able to think: at least we're a couple gigawatts to the good. Not to mention the fact that 660 turbines spinning like garden pinwheels would be a sight to behold.

— Cecil Adams
Photo by Cody Pomeroy. Used with permission.

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