Solar powered hang gliders

A discussion restricted to the topic of hang gliding.
LegendLength
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Solar powered hang gliders

Post by LegendLength »

Just as a thought experiment, I wonder if it would be possible to drag a large, flexible solar panel array behind a hang glider to use as a battery?

Even if money, weight and flexibility were no problem, it seems to me that dragging a 20 meter long piece of solar 'carpet' behind you may work but with aerodynamic problems. I thought about maybe rolling the flexible solar rectangle into a cylinder that is towed behind instead. This seems more aerodynamic to me. Or cutting it up into long 'streamers'.

Takeoff and landing could perhaps be solved by rolling the device up into a rectractable system behind the glider.

One other thought was to have no trailing battery, just cover the hang glider's wing in solar panels. I have read that this is not enough power to fly but what about combined with pilot foot/pedal power?
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Davis
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Post by Davis »

The internet, it's a powerful way to answer your questions if you are willing to make a little effort. In the dark ages people had to ask others or look in a book when they had a questio. They couldn't perform a search and find the answer for themselves. But that was then, and this is now.

Somehow the name Eric Raymond floats through my mind.
LegendLength
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Post by LegendLength »

The internet, it's a powerful way to answer your questions if you are willing to make a little effort.
I find that a little condescending after searching online for a few days straight.
Somehow the name Eric Raymond floats through my mind.
I actually did come across the Sunseeker early on. It is a great machine but I am more interested in the aerodynamics of dragging any type of static device or 'cloth' as a battery, to allow cheaper solar cells to be used. I'd also like to know anyone's ideas of combine solar and foot power in a glider (I couldn't find if Eric was using foot power as well).

If was a dumb question then I apologize and hope that I did not waste anyones time too much.
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Andy
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Re: Solar powered hang gliders

Post by Andy »

LegendLength wrote:...would be possible to drag a large, flexible solar panel array behind a hang glider
That's just it - lots of drag. In order for it to have enough power, it would have to be huge and that would be way too much weight and drag. Have you ever seen a banner plane struggleing to tow a big banner? They've got about 160 hp. I remember reading somewhere that today's best solar panels are something like 15% efficient. It needs to get up around 90% to be really practical for something like this. And I think the best place would always be on top of the wing.

Andy
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Davis
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Post by Davis »

Sorry for being condescending, but so often we get questions before anyone has made the effort to try to find the answer. Best to indicate that you've made an honest effort by pointing out what you've found and how it didn't address your question and specifically how that answer is different than the one you want.

Yes the Sunseeker is what I was referring to.

http://ozreport.com/9.043

Check here: <a href="http://ozreport.com/search.php?hl=en&lr ... tnG=Search">
Eric Raymond</a>
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Jacmac
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Post by Jacmac »

There is actually quite a bit of development going on in the area of flexible organic solar cells which may be woven into fabric. These solar cells have a vastly improved efficiency, on the order of 4 or 5 times more efficient and they are light weight. Some day the sail of a glider could be a large solar cell.
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Andy
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Post by Andy »

I found the article in the June edition of National Geographic. It says traditional solar cells convert nine percent of the sun's energy. One of the latest technology solar panels (using nanotechnology to create a flexible, inexpensive panel) claims a 12 percent efficiency.

There are solar cells that claim a mid-thirties efficiency, but they use expensive materiels and most importantly use optics to concentrate the sunlight on the cells, making this rather impractical for flight (this from some quick internet research I just did).

The drag caused by towing a solar panel behind an aircraft is absolutely unnecesary and impractical when mounting what is already by it's nature a thin flat panel on the wings adds virtually no drag. When you drag a flexible sheet in an airsteam, undulations of the material cause even more drag. If you stiffen it with structure, you add more weight. To stabilize it with control surfaces to face the sun, you add more weight and drag. And so on and so on....

The practicality of using solar panels on an aircraft is best utilized I think with a glider and mating the cells with very efficient, light weight batteries and should not be too far off. This gives you bursts of power when you need it (launch, low saves, etc.) and allows the batteries to recharge while soaring.

Andy
Last edited by Andy on Mon, Jul 31 2006, 12:27:09 pm, edited 1 time in total.
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Jacmac
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Post by Jacmac »

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Andy
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Post by Andy »

That article says they only get 3.6% with their solar cells....
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Jacmac
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Post by Jacmac »

Yeah I think I was seeing a efficiency ratio that was based on weight, not surface area. The new technology is supposed to be far lighter.
Going dotty
If the mysterious multiple-exciton effect pans out in practical devices, solar cell efficiencies could soar, scientists say. Both the Los Alamos and NREL teams calculate a maximum of 42 percent conversion of solar power to usable electricity. Conventional cells, by contrast, operate at 15 to 20 percent efficiency.

Some researchers have made prototype photodetectors and solar cells from quantum dots. For instance, Difei Qi of Louisiana Tech University in Ruston and her colleagues mixed a conductive, photosensitive polymer known as MEH-PPV with lead selenide quantum dots. Under visible light, a device incorporating dots at only about 5 percent by weight generated 50 percent more current than expected if each photon yielded one exciton, the Louisiana team reported in the Feb. 28, 2005 Applied Physics Letters.

More recently, a Texas team working with Klimov and Schaller made experimental solar cells by blending 8-nm-diameter lead selenide quantum dots with another conductive polymer called polythiophene. "We see a dramatic increase in photocurrent at exactly three multiples of the band-gap energy," says Anvar A. Zakhidov of the University of Texas at Dallas in Richardson. That current ramp-up indicates that photons are producing multiple excitons, he reported last March in Baltimore at a meeting of the American Physical Society.

Despite such encouraging signs, before highly efficient solar cells appear, "there's a lot of work to be done," Nozik cautions.

Generating extra excitons might also have a major impact on equipment that uses solar energy to split water to extract its hydrogen for various uses—for instance, to energize fuel cells—Klimov says. Each water-splitting reaction requires four electrons, he notes, so the more electrons per solar photon the better.
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