Indiana wind farms (WITH LINK TO COLUMN BY CECIL)

In a message dated 12/10/2009 7:02:58 P.M. Central Standard Time, writes:
Dear Cecil, I drove to Indianapolis Monday, Dec. 7 to attend the baseball winter meetings. As I drove south on I-65 through the beautiful cornfields of central Indiana, somewhere near Rensselear, on the east side of the interstate, I encountered a huge “wind farm”, with dozens and dozens and dozens of huge wind turbines, stretched out as far as the eye could see. ( Sort of made me think of a 50’s Si-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 mingle and try to make deals on cocktail napkins, while avoiding the national and local press in the hotel bar, it was time to drive back to good old Chicago, Illinois on Wednesday. As you may recall, Wednesday, Dec. 9th, was the snow storm/blizzard across middle America, with winds howling from Wyoming to the Eastern Seaboard. ( Tom Skilling, Tribune 12/10: “…Wednesday 8am and 9am barometric pressure — 28.91” — was the lowest since October 1990 with 28.81" with 57 mph winds in Coal City, IL, and 51 mph in Kankakee…" ) So, while driving back home north on I-65 around noon Wednesday, and the wind gusting at over 50mph, I was looking forward to observing the wind turbines spinning around madly like my electric meter in the summer with all the A/C running. But, always expect the unexpected, eh Cecil? When I drove passed the “farm” this time, 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 to generate electricity of all time due to some goof-ball accidentally throwing the wrong switch at wind-mill-command. Or, could it be that these big turbines can’t handle it “when the wind comes whipping off the plains…”? If so, what a waste. I know you can help me unravel this paradox in the windmills of my mind. Thanks, MM.

Mike Murphy

Well, if you don’t shut down wind turbines in high wind conditions, this kind of thing can happen. The description of this video says that the wind speed was around 65 mph. If you watch this video carefully, it looks like one of the rotors breaks under the force of the wind; that causes the whole assembly to become unbalanced, which brings down the whole damn thing.

If one of those wind turbines along I-65 were to fail in this way, I would not want to be driving by at the time.

With reference to the subsequent column…

It seems that the extra energy available from very high winds is a lot to give up. It occurs to me that possible solutions are:

  1. Shift gears and gear it down. The generator portion of the system would be running at normal speeds. Only the blade mechanism need be designed for extreme conditions.

  2. Feather the blades, but not all the way, just enough to reduce the rotation speed to max-normal. In other words, make them only marginally efficient. You would still have to deal with vibration, but you have to handle that even if the blades are standing still.

Any reason why these ideas wouldn’t work?

I once saw a news announcement a few years ago about a revolutionary new wind energy capture device that does away with the need to convert the torque produced from horizontal to the ground (as in the standard wind turbine depicted). In other words, it does not require gearing to convert torque from horizontal to vertical in order to transmit the said torque to the base of the pylon. One of the touted advantages was that there was no need for a shutdown in (those potentially highly productive) high winds. It also took up a lot less space than those gigantic airplane propellers you see out in the boondocks, looking as it did, a little like an enlarged DNA helix inside a cylinder. Whatever happened to that invention?

A little wiki-ing gave me the Quietrevolution turbine, which is a variant of the older Darrieus turbine. Is this what you saw?

Also: Wikipedia’s article on wind turbines has a list of advantages and disadvantages of both horizontal- and vertical-axis turbines. At least two of the disadvantages (lower rotors giving less power, and cyclic stresses on the rotor blades) would seem to be inherent to vertical-axis designs.

Finally, I always thought that the generator assembly for a horizontal-axis turbine was located at the level of the hub, and that it was electricity (not torque) that was transmitted to the ground. I could be wrong, though — any turbine engineers want to chime in?

As MikeS points out, the rotation from the blades is typically converted to electricity at the top of the tower, not the bottom. Some of the generators are automobile-sized units (I’ve seen a comparison picture of turbine vs. VW bug on the ground). Although it’s a heavy component to have to lift and mount high up, its easier than trying to transmit mechanical energy to the ground.

No, I’m not a turbine engineer, I’ve just attended a lot of wind energy and public hearing seminars.