Next Generation Energy

Typical wind velocities near the ground are measured in the single-digit kilometers per hour. They can get a bit stronger, but most wind turbines have to shut down when the wind really starts to blow. Which is a shame.

Higher up in the troposphere though, wind velocity is much greater. In the graph at right, taken from "Design and testing of a remotely controlled surfkite for the Laddermill" by Bas Lansdorp, B. Remes
and W.J. Ockels of Delft University in the Netherlands, we see that wind speeds in the air over Holland peak 10 km up at better than 45 knots. Wind up there also blows more reliably. So what would it take to exploit all that free kinetic energy?

A series of kites known as a "laddermill," of course. It's just one of several ideas floating around to exploit high-altitude winds. They all share the same basic concept, and as usual, someone else can explain it better than I. Here's Michael Brooks in New Scientist (sub. req'd) just a few weeks ago:

The basic idea is that, just as a yo-yo spins when its string unfurls, so an electrical generator can be driven by the pull of a kite's aerofoil.... the kite is flown on two tethers, each one held on a separate drum attached to a computer-controlled winch. Once the kite is launched and in stable flight and pulling on its tethers, the winches are released. The tethers then reel out, spinning the generators. When nearly the entire length of the tethers has unspooled, the winches are engaged to haul them back in, returning the kite to its original position.

How much power can such things generate? Well, since power is proportional to the cube of wind speed, in theory quite a lot. Though no one has successfully scaled up any of the tiny kilowatt-range prototypes, the Delft team optimistically predicts 50 megawatts for a full-size version of their experimental model. Even if the real output is closer to one tenth of that, we're still talking about something bigger than most existing wind turbines. And there really isn't a lot of fancy, expensive equipment to develop. Just very strong, very long strings, along with computers to handle them.

Again, we're not likely to see such stuff dominating our skies any time soon. But as with many other technologies, it might make sense in remote, lightly populated places with little competition for the airspace, and where running grid lines is too expensive. More important is the example kite power sets for others trying to dream up way to taking advantage of free kinetic energy, which is just another manifestation of solar energy, of course. It's all there for taking, if we can just put our minds to it.

At least, that's the kind of thoughts I entertain when I get depressed about our lack of progress on the clean energy tranformation challenge, and the rapidly dwindling window of opportunity remaining before it will make no difference.