Cut-in Speed in the Doldrums

« « Ethanol Fuel Cell – Learning about the Effectiveness of It | Solar Power Cars - The Pros And Cons » »

Sunday, August 30th, 2009 Subscribe To Our Feed

An evening walk with my wife revealed to me something about wind turbines. We were walking in a garden that happens to be set in a valley right below two large industrial turbines. I bet these have cut-in speeds of 20 mph (granted- I’m familiar with home, rather than wind turbines, but I’m sure they require a lot of wind). In addition, the two turbines are two different sizes. By swept area, I’d think that one is at least 1/3 bigger. This area also does not ever appear to be windy. I had often commented to my wife how odd I found it that such large turbines could function right there- it feels like the doldrums of a desert landscape

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.

But then something interesting happened. The Earth cooled, night fell, and the turbines started spinning. More interestingly, the larger turbine seemed to start moving slower than the small one, but as night progressed, began moving faster and faster till it seemed to be moving even faster than the small turbine. Despite their weight, the larger blades simply caught more air, making them move faster than the smaller blades.

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.

Share and Enjoy: These icons link to social bookmarking sites where readers can share and discover new web pages.