I picture it as a long oval track. The kite tacks back and forth to maintain the proper thrust vector. It's the ends of the oval that make the problem interesting. Maybe, if the oval were narrow but long, as the generator car enters the curve the kite begins to tack, pulling it into the curve. generator car momentum would finish the direction reversal.
Eight kites, flying in formation, tacking back and forth, that would be an interesting sight to see.
They tested it first on a straight track but further testing will be done on a looped track to see how that works out. Eventually control of the kites will be automated by a computer. I'm sure the kites themselves in the air are a sight to see! Seems like a rather beautiful way to generate energy.
Liz, thanks for covering this--what fun, how elegant, and I like the lower environmental impact of the technology. While most wind turbines don't go as high, the one we wrote about here http://www.designnews.com/document.asp?doc_id=243636 is designed to eventually achieve over 1,000 feet in altitude.
Am I missing something? How could the generator car possibly "loop back" when the kites are pulling in a vector that probably won't vary by more than 45 degrees? Assuming a long narrow oval track at 90 degrees to the wind, on the straight legs of the oval the kites would only be providing a portion of the total force anyway: moving the generator first to the left, say, on the up wind straight leg, then following the wind direction through the first curve, then the kite would have to tack to the right, pulling the generator to the right on the downwind straight leg, then it would get to the next curve, somehow proceed against the kite force and midway through the curve the kite needs to reverse tack to the left, the generator still working against the kite to get back to the straight leg. If this works they've discovered perpetual motion.
I wonder if they've thought about potential aircraft collisions. In Illinois, where I live, it's very easy to spot wind turbines at night because wind farms typically have synchronized red lights that blink on and off at night. Could they do the same with kites?
I didn't want to say anything from an aviation standpoint, because that's something I'm a little biased on. Since the door's been opened, I think it's outrageously dangerous to have a kite above 1000' AGL. Yes, there are antennas that reach that high with nice, bright beacons, and one can assume that the kite would be as well lit, but the problem with a kite is that you have no way of knowing where the aluminum shredding tether is going to be. There was a story similar to this before, and I likened the tethered, airborne windmill to a WWII era barrage balloon, and certainly, the effect to a passing aircraft would be similar.
Excellent points about aircraft concerns. Lights could be one option; however, I'm sure as this system continues to get tested this will be addressed. One easy solution would be to try to put them in areas where there aren't often low-flying craft. Staying far away from airports is an obvious solution to that.
I think the only solution for aircraft concerns would be to ban aircraft from the area entirely. This is especially true since in the US, aviation is moving away from flight paths to routes decided by pilots through GPS tracking.
This is not unprecedented. There are many areas off limits to aircraft already.
It does remind me a bit of barrage balloons during Word War II I read about.
No, mrmikel, most General Aviation flights are still Visual Flight Rules. Commercial Aviation typically flies Instrument Flight Rules and at altitudes that wouldn't cause any problems to this system, but small planes would have real issues.
Very interesting and definately a more aesthetically pleasing energy source! I wonder what their flight ceiling would be and if its regulated...as a model rocket hobbyist, I have been told of the heightened security after 9-11 to include a more restricted flight ceilings. Since this technology is airborne - I wonder if it has to coordinate with the FAA?
Excellent point, Nancy. Since this is just being tested in Germany right now, it remains to be seen if this method comes stateside. I imagine there would be some concerns with air traaffic as well, depending on locations and how high the system can be built.
It might be very similiar to model rocketry protocol - waivers sometimes have to be filed and approved with the FAA and flight patterns have to meet certain criteria. That would probably be a good way to deal with air traffic. We wouldn't want a model rocket crashing through one of those kites!
A close view of the picture shows four lines going to the kite. This might imply that that 4 lines are needed for strength and or redundancy. However, it also implies that the kite would be capable of being directionally controlled (tacking) allowing it to fly in directions not directly downwind. Nothing mandates that a track mounted generator can't store enough power to propel itself while tacking crosswind down a track perpendicular to the wind for the brief period needed to navigate the half loop at the end of an oval track. Then there's the design study needed to show if a figure 8 track (allowing more downwind travel) of a given distance would provide more net power than an oval track with a given diameter at the ends.
Unlike solar farms or windmills which are inherently difficult to look at or follow with the eyes, advertisers could use these kites to place their logos on truly unobstructed billboards, and not cut down any trees in the process. So capitalism could serve environmentalism for a change. And vice versus.
Of course, the kites would have to fly in a public area, but those are the small details. : )
The version of the kite-type system that I saw that made more sense put the turbines up in the kite. The generators could be run as motors to fly up into the wind area, thgen revert to generating power from the high altitude wind. The major problem with this approach was the transmission of the power back to the ground. My suggestion is to use quite high voltage and separate cables for each phase. Then you could have a twenty kilovolt transmission line with fifty feet of separation. It really is an interesting concept, and less complex than flying a kite in circles. I was never able to do that in a sailboat, so why should it be any easier with a kite.
"the faster a kite flies the harder it pulls". Meh. Last I checked, kites were pretty much stationary in the sky and the wind moved past them. This statement makes no sense.
Yes, if you pull in the kite it will pull harder because you are increasing the relative wind speed the kite sees. But a kite is basically a stationary device that provides lift when air moves past it.
It strikes me as they are chasing an awkward way of achieving power with railway tracks and the like.
A far simpler way would be to build the kite so you could dynamically play with the lift and drag, and operate the kite in "cycles". You would set up your kite cable winches to be able to spool the cable in and out, and any necessary braking on the winch drum(s) would be converted to useful energy.
The first part of a cycle would be with the kite flying high, at the desired high altitude, (read: higher wind speeds) but pulled as close in to the winch point as possible. Now, change the kite characteristics to get maximum drag while just maintaining the desired altitude. Begin letting out cable and harvest the energy from the pull of the kite. Depending on the airspace you are allowed to operate your kite in, this may be many thousands of feet downrange.
Once the kite has reached the far end of the cycle, you need to bring it back to the starting point. Presumably, from the data the company has provided, there are lower wind speeds at lower altitudes. Therefore you pilot the kite, again by playing with lift and drag on the kite, to minimize the drag and allow just enough lift to bring it back upwind with your winches, presumably expending less energy than your gained by the wind towing the kite downwind.
Sounds like a cumbersome way to harvest wind energy.
While the Benjamin Franklin kite story is known to just about everyone who went to elementary school in the U.S., it's almost certainly untrue. Franklin wrote an article suggesting a version of the experiment, but he didn't claim to have actually performed it himself -- and if he had done it the way it is usually described, it's unlikely that he would have survived.
That being said, I teach a U.S. citizenship class, and always mention the kite story to my students (along with the story about George Washington and the cherry tree, which is also probably a legend). First, because it's a story that most people who grew up in the U.S. know, and is a part of our popular culture. Second, because Franklin's scientific fame helps explain why he was chosen to be the U.S. diplomat to France during the Revolutionary War, which is what USCIS thinks you ought to know about him.
I always have difficulty with what is and is not practical. Years ago, I thought airbags were the most illogical devices known to man and yet today, they save countless lives each year. This approach to harvesting the wind is definitely unique but as others have mentioned, the concept seems to be laden with complexities that would make the application very unreliable. Obviously a complement to existing power sources, I would imagine a "hit-or-miss" situation at best. Very interesting though and thanks Elizabeth for writing about this one.
Thanks for your comment, bobjengr. I hear what you're saying and think there are a lot of issues with this idea to be solved before it would actually be viable. But if anyone can come up with answers, the Germans can! They are doing remarkable things in wind energy. I guess time will tell.
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