Cut-in Speed in the Doldrums

I live in the kind of area that looks on a wind map like it could never possibly support a wind turbine. One of my favorite places to go walking with my wife is under two giant (I’d guess 100 meter) wind turbines. One is larger than the other. I had commented to her how amazing it as that these things moved at all. Granted- their location is carefully thought out and they are placed incredibly high. But still- it had long surprised me that they moved at all.

When I was out there last night, I noticed for the first time that the larger turbine wasn’t moving at all and the smaller one was barely moving. “Sort of figures, I thought.” It was a clear demonstration of a particular phenomenon to me- cut-in speed. This is the speed necessary to move a wind turbine. Clearly, the light breeze wasn’t doing it. It simply didn’t move fast enough to move the big turbine or to move the small one in any significant way.

Then night started falling, the Earth cooled down, and canyon breezes began anew. Pretty soon, both turbines were turning. I noticed a particularly interesting phenomenon at this point. Just before dusk, the smaller turbine was turning faster than the large one. Then as wind picked up more and more, the larger turbine was actually making more revolutions than the smaller one.

This was a real-life demonstration of something I’ve preached about in teaching people how to size up a wind system. In all the buying guides, wind-tower specs, and so on, it’s always important to consider cut-in speed. If you can find a place on your property that consistently gets 12 mph of wind, all the better than finding one that gets 8 mph. And at that point, consider whether you want something with a cut-in speed of 8 mph or one with a cut-in speed of 10 mph. The truth is that the latter will probably produce more power. So instead of thinking of this simply conservatively, perhaps we should consider the total picture and think that larger turbines might benefit us in ways that the smaller ones will not.

And as always- good luck building!

Damon Westchester is the editor of build-green-power.com.

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