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Research team is looking to make solar panels more efficient and give LEDs color changing capability

A pair of researchers at Arizona State University has announced a new advancement in making nanowires that could one day lead to significantly more efficient solar panels and LED lighting that is color changeable. The engineers who made the advance are Cun-Zheng Ning and Alian Pan.

The pair are working on ways to improve the quaternary alloy semiconductor nanowire raw materials. The nanowires the pair work with are nanometers in diameter and tens of microns in length. They are made from four elements, typically by alloying two or more compound semiconductors.

The researchers say that the band gap is the most important thing that controls how solar panels absorb sunlight and what color light LEDs produce. The more available band gaps for solar panels, the more of the spectrum of light panels will be able to absorb. With LEDs, more band gaps mean more colors of light can be produced. 

The big hurdle for the researchers is that naturally occurring and manmade semiconductors today only have a specific band gap. The only way to widen the band gap available to the semiconductor is to compound two or more semiconductors. The trick to accomplishing the alloy of semiconductors is that they two have to have a lattice with similar inter-atomic spaces to match and be grown together.

Ning said, "This is why we cannot grow alloys of arbitrary compositions to achieve arbitrary band gaps. This lack of available band gaps is one of reasons current solar cell efficiency is low, and why we do not have LED lighting colors that can be adjusted for various situations."

So far, the team has been able to create a zinc sulfide and cadmium selenide alloy to produce a quaternary semiconductor – this is the first time that a quaternary semiconductor has been produced in the form of a nanowire or nanoparticle. The team is now studying the application and use of the quaternary alloy materials for making solar cells and has developed a lateral multi-cell design panel.



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RE: Promises promises
By porkpie on 3/22/2010 1:05:28 PM , Rating: 3
There are countless problems with this. First of all, his numbers are far off base. Assuming 50K miles of Interstate Highway and an average width of 50 ft (4 lanes), that works out to 500 sq. miles. Assuming 20% efficient solar cells, though, would require an area 100 times as much -- 5,000 square miles, not even counting tranmission line or storage losses:

http://www1.eere.energy.gov/solar/myths.html

Then there's the problems. #1 is that transmitting energy over 50,000 linear miles would result in line losses eating up nearly all the generated power. You could cut that by using HVDC technology...but 50K miles of HVDC line and upconverters every mile or two would bankrupt the nation.

Covering the interstates would require you to either light them underneath (using more power) or have drivers in the dark 24 hours a day. You'd need support posts strong enough to survive a car impact (increasing the risk to drivers) or else every time a car veered off the road you'd take out a section of pricey solar panels...and drop them right onto the road, in the path of other drivers.


RE: Promises promises
By SPOOFE on 3/22/2010 4:03:20 PM , Rating: 1
First off, your own numbers are off.

"...a minimum of two travel lanes in each direction, 12-foot lane widths, 10-foot right paved shoulder, and 4-foot left paved shoulder."

http://www.fhwa.dot.gov/programadmin/interstate.cf...

That puts your estimate at least 25% too low, and that's not including non-paved land (like the central median) that the Feds also own along the highway routes.

Further:
quote:
would require an area 100 times as much

To do what? Provide a significant percentage of our electricity needs?

quote:
#1 is that transmitting energy over 50,000 linear miles would result in line losses eating up nearly all the generated power.

Who said anything about transmitting energy over 50,000 miles? Most of the electricity generated would be within 100 miles of where it would be used.

quote:
Covering the interstates would require you to either light them underneath (using more power) or have drivers in the dark 24 hours a day.

A 75-100 foot wide overhang would be pathetically insufficient to block out a significant portion of sunlight bouncing off the ground and atmosphere, much less leave them "in the dark".

quote:
You'd need support posts strong enough to survive a car impact

Uh, naturally.

Sorry, Pork, but compared to your usual posts, these are some very weak nitpicks. And again, it was mentioned only to point out the flaw in "land use" arguments: The land is there, and there's a lot of it.


RE: Promises promises
By porkpie on 3/22/2010 4:36:00 PM , Rating: 3
"That puts your estimate at least 25% too low, and that's not including non-paved land (like the central median)"

So? Even if you double my initial estimate, its still only 1/50 the amount of land you need, even ignoring the vast amounts extra needed due from energy storage and transmission losses.

"You'd need support posts strong enough to survive a car impact... Uh, naturally."

You agree, but you don't see the implication. 100,000 miles (50Kx2) of concrete support posts, topped by steel supports at least 20' tall and strong enough to survive the impact of a truck moving at highway speeds...do you have any idea how much that would add to the cost of the proposal? Or the gargantuan amounts of materials it would entail, regardless of cost? Materials that would need to be continually maintained on an annual basis?

"A 75-100 foot wide overhang would be pathetically insufficient to block out a significant portion of sunlight bouncing off the ground"

Huh? Look at any current Interstate overpass. If it's wider than 60 feet (five lanes), the space below is lit. A strip 75' wide and miles long would block out a large amount of sunlight...unless you elevated the strip more than 20-25' in the air (which itself causes significant problems).

"Most of the electricity generated would be within 100 miles of where it would be used."

No. Look at a map of the Federal highway system...most of those highway miles, especially in the Western US, are well outside major population centers.


RE: Promises promises
By SPOOFE on 3/22/2010 4:52:26 PM , Rating: 1
quote:
So? Even if you double my initial estimate, its still only 1/50 the amount of land you need, even ignoring the vast amounts extra needed due from energy storage and transmission losses.

Again, to do what? What do you think the proposal is suggesting?

quote:
You agree, but you don't see the implication.

I see it very well. It just means it would be expensive, which is a single problem... quite a distance from the "countless" problems you mentioned. Please, identify some of these other "countless" problems.

quote:
Huh? Look at any current Interstate overpass.

I do. Regularly. It's called "shade". It looks darker in pictures due to contrast and poor dynamic range. It's NOT "in the dark" as you suggest, nor does it necessitate lighting.

quote:
No. Look at a map of the Federal highway system...most of those highway miles, especially in the Western US, are well outside major population centers.

I'm looking at the map right now. The Eastern United states would put most of the highway system within some dozens of miles of population centers... and regardless, it's still nowhere near your silly notion of transmitting the power 50,000 miles.

Again, Porky, not your best nitpicks.


RE: Promises promises
By porkpie on 3/22/2010 5:39:46 PM , Rating: 3
"What do you think the proposal is suggesting?"

By your own words, you suggested the amount of land was enough to provide "a fat percentage" of the nation's power. If something between 1 and 2% is "fat" in your book, then I concur.

" It just means it would be expensive, which is a single problem... quite a distance from the "countless" problems you mentioned. Please, identify some of these other "countless" problems."

I identified several, the two largest being a) the amount of land is only enough to provide a tiny fraction of our power needs, and b) Highway siting would be far more expensive than using undeveloped land somewhere, despite the space above the highway being "free", due to the need for elevated supports.

If you think that's still a viable alternative just from those two factors alone, I don't know that continuing the discussion will be fruitful.

" It's called "shade""

This is a little silly. A tunnel 100' long is quite dark in the middle. Is it as black as the depths of a moonless night? No, but its certainly in the twilight realm, and dim enough to require car lights, or some other source of lighting.

Take a look at any large wall-less structure, for instance a large horse arena. There's one near my house, that is roughly 100' x 300'...and lit from above, even during daylight shows...and it gets additional light from all four sides, which a miles-long highway would not.


RE: Promises promises
By SPOOFE on 3/22/2010 6:30:35 PM , Rating: 2
quote:
By your own words, you suggested the amount of land was enough to provide "a fat percentage" of the nation's power. If something between 1 and 2% is "fat" in your book, then I concur.

But we've already seen that your numbers are hasty, inaccurate, and low-balled.

quote:
I identified several, the two largest being a) the amount of land is only enough to provide a tiny fraction of our power needs, and b) Highway siting would be far more expensive than using undeveloped land somewhere, despite the space above the highway being "free", due to the need for elevated supports.

You had two insignificant quibbles, the first of which was sloppy math on your part, and the second of which simply observed that we can't build these things out of stacks of newspaper and Q-tips. That's hardly "countless".

quote:
If you think that's still a viable alternative just from those two factors alone, I don't know that continuing the discussion will be fruitful.

You tell me if I think it's a viable alternative. Hint: I say as much in my very first post. I'm sorry your heightened emotional state has hampered your literacy.

quote:
This is a little silly. A tunnel 100' long is quite dark in the middle.

The word "tunnel" does not at all describe the described structure. I don't even know how you got that. The fact that you would even suggest that as a real counter only throws doubt on everything else you're saying.

Anyway, a "tunnel" has stupidly narrow apertures at either end, relative to the volume contained therein. A road covering would have exposed sides and let in orders of magnitude more light relative to volume.

quote:
Take a look at any large wall-less structure, for instance a large horse arena. There's one near my house, that is roughly 100' x 300'...and lit from above, even during daylight shows

For comfort, not by necessity. Attendees to a large event do not come with a pair of powerful lights attached to their faces, in addition. Again, it does not seem like you have any coherent argument; it's like you're just shouting the first thing that pops up in your ADD mind.

And, again, since you don't seem to know what you're arguing: The point was raised only to demonstrate the availability of land. I never presented it as a viable option; only your hasty fevered mind interpreted that. The land is available, public, very undeveloped for the most part, stupidly accessible (as opposed to the "middle of nowhere" option you presented), and most importantly, would cost nothing to acquire.


RE: Promises promises
By porkpie on 3/22/2010 7:03:09 PM , Rating: 2
"But we've already seen that your numbers are hasty, inaccurate, and low-balled."

Come now, don't descend to hyperbole. Even taking into account your objections on road width, it only boosts my figure from 1.0 to 1.25%...and we still haven't subtracted what's necessary for transmission and storage losses. I am generously positing a value as high as 2%.

Is 2% a "fat percentage" of our nations electric needs? Yes or no.

"The word "tunnel" does not at all describe the described structure"

It most certainly does. A strip several miles long is effectively enclosed front and back -- zero sunlight will penetrate that far. It's also enclosed top and bottom.

That leaves two sides for light to penetrate. If the strip is 100' wide, that's equivalent to a tunnel 100' long. Mathematically, they are equivalent. Would you prefer it if I formulated it as a formal boundary value problem?

"The land is available, public, very undeveloped for the most part, stupidly accessible (as opposed to the "middle of nowhere" option you presented), and most importantly, would cost nothing to acquire."

That certainly sounds like you're calling it a viable option. Which one is it? If you don't consider it viable, why are you fighting so hard to portray it as such?

And while this "land" would cost nothing to acquire, it would cost at least 10X as much to cover with solar cells as would an equivalent sized piece of undeveloped land, far outweighing any savings in acquisition costs. We have even more "free land" in the open ocean. Does that mean floating solar cells in the middle of Pacific is a better alternative than putting them in the NM desert?


RE: Promises promises
By Keeir on 3/22/2010 7:21:28 PM , Rating: 2
Here... let me add some numbers.

The US currently produces/uses ~
4 x 10 ^15 Wh a year.

Solar Insolation
http://rredc.nrel.gov/solar/old_data/nsrdb/redbook...
I assumed Horizontal Flat Plate.

Across the US, we are looking at an Average of ~ 4500 Wh/m2/day

A really good solar panel is 20% efficient.

So that leaves use with

4 x 10 ^ 15 Wh / 4500 wh /356 days * 1 m2 / .2 efficieny = 12.45 x 10 ^ 9 m2 or about 4,800 square miles

Since you have decide that 100' wide or so is adequate, we would need approx 250,000 miles of roadway to provide 100% of the power needs, at generation source. This of course leaves off the ~10% due to current lines losses, which I can't imagine would get any better with the above system. In fact, assuming 10% line losses and near magical 20% solar panels, covering the entire ~47,000 mile could provide ~16%. I guess we could describe that as fat.

Oh, and for your information, the structure we are talking about would be a continous strip of solar panels with no breaks. It would need to be mounted a minimum of 33' in the air if you didn't want to light the area underneath and even higher in some situations. A larger problem would be the wind breaks. Since a 100' wide structure would likely catch the wind, we would need to design in ways to lighten the wind load... which would let direct sunlight down below... which is in turn would likely require the additional lighting as Human eyes can't really adjust that fast.

I doubt covering the entire US highway system would result in more than 10% of our power needs... and I doubt it could be accomplished much less than the original cost of the system (~425 Billion dollars).

(Oh by the way, nothing can really help the system if a tractor trailor full of gasoline smashes into a post. A large section will be destroyed... there are reasons why that land is not readily availble.)


RE: Promises promises
By porkpie on 3/23/2010 4:04:26 PM , Rating: 2
Spoofe, I'm going to cede the land use point to you. I made a rather shocking math error. I correctly calculated ~500 sq m for road usage, and 5000 sq. miles required for power-- but then somehow read (a) as being 1/100 of (b), rather than 1/10.

So yes...if you could solve the other myriad problems, this would give you enough land to power a 'fat percentage' of our electric needs.


RE: Promises promises
By JediJeb on 3/22/2010 5:52:10 PM , Rating: 2
quote:
quote: So? Even if you double my initial estimate, its still only 1/50 the amount of land you need, even ignoring the vast amounts extra needed due from energy storage and transmission losses. Again, to do what? What do you think the proposal is suggesting?


I have to agree with Spoofe here, that is a valid argument if you are trying to supply the total electricity the US needs, but if you are trying to offset some then it is more than sufficient. It is like saying to provide the total US electricity supply with hydroelectric you would need to flood an entire state. The original idea was to offset some energy needs, that of a large city, not an entire country. But if you were using this only to offset NYC then yes you would need the 50K miles of transmission lines, but to offset the amount of electricity NYC uses but spread across several large cities then it would not be such a problem.

quote:
quote: Huh? Look at any current Interstate overpass. I do. Regularly. It's called "shade". It looks darker in pictures due to contrast and poor dynamic range. It's NOT "in the dark" as you suggest, nor does it necessitate lighting.


Here I would also expect the sides to not be touching the ground, if they are 20feet high then a lot of light is going to get under them. Also the added benefit of a shaded highway would reduce gasoline consumption in summer as the A/C would not be working as hard to combat the heat of the sun on the cars, and personally I prefer not driving in super bright sunlight, as the dimmer light of an overcast day is much easier on my eyes when driving so this would help also. Dry pavement versus wet pavement driving is also something to consider. Reduction of cost due to snow removal in winter and no road salts needed also helps not to mention less corrosion of vehicles from said salts.

Can't overlook the side advantages to this idea. I doubt it would ever be fiscally feasible but not totally without merit.


RE: Promises promises
By porkpie on 3/22/2010 6:13:25 PM , Rating: 2
"but if you are trying to offset some then it is more than sufficient."

If you're trying to offset just 1-2% of our electric needs by spending tens of trillions of dollars, then yes, this is more than sufficient.

"Reduction of cost due to snow removal in winter..."

If you don't remove the snow from the solar panels, how do they generate electricity? You can simply slant them...but you'd need a pitch close to 10:12 to reliably shed snow. Not only does that reduce efficiency -- even in summer months -- but it means a peak height of 105 feet for a 100' wide highway. That's a big structure to build 50,000 miles of.

"Can't overlook the side advantages to this idea."

Sure, there are some. There are also far more side disadvantages that I didn't even mention. Things like maintenance....how do you work on solar panels above a highway filled with rapidly moving vehicles? Stop traffic? Or build the panels strong enough to be walked on from above? (adding even more to the cost).

Face the facts. Using the "free space" above highways would be far more expensive than just using some undeveloped land somewhere. It's just not a practical idea.


RE: Promises promises
By bh192012 on 3/22/2010 7:49:11 PM , Rating: 2
Probably based on something like http://www.planetthoughts.org/?pg=pt/Whole&qid=314...

(which I'm not saying it's true, this is the internet... just citing a source)

cross that with things like http://www.ecogeek.org/content/view/991/

Big solar makes good sense in the south. Lots of air conditioners running, offset by lots of PV. Plus lots of land in the southwest etc. Probably doesn't make sense in the north east where it's cool and dim. Build nuke plants there, then upgrade the grid so they can shuffle power back and forth effeciently between nuke and PV.


RE: Promises promises
By bh192012 on 3/22/2010 7:54:55 PM , Rating: 2
Ohhh, and don't build over the highway.... we've got plenty of regular open space in the parts of the country where this makes sense.


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