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Research Promises Full-Spectrum Solar Cell
nphillips writes "As is being here reported here, a serendipitous discovery was made that a single system of alloys incorporating indium, gallium, and nitrogen can convert virtually the full spectrum of sunlight -- from the near infrared to the far ultraviolet -- to electrical current. For if solar cells can be made with this alloy, they promise to be rugged, relatively inexpensive -- and the most efficient ever created. Solar cells so efficient and so relatively cheap could revolutionize the use of solar power not just in space but on Earth."
Better than 70% efficency, versus 25% for current solar cells. Ok, now im willing to accept solar might be feasable.
All Troll + "offtopic" mods are meta moderated as "Unfair", because you abused the system.
vaporware!
and I quote
"In MBE the components are deposited as pure gases in high vacuum at moderate temperatures under clean conditions."
Further
"If it works, the cost should be on the same order of magnitude as traffic lights," Walukiewicz says. "Maybe less." Solar cells so efficient and so relatively cheap could revolutionize the use of solar power not just in space but on Earth."
-- The morphemes of your disquisition are ascertainable, but they have eschewed an ambit of transpicuous exposition.
As I understand it, UV light hits the earth at all hours.
UV or IR? I've never head of UV light reaching the dark side of the planet in any quantity (other than whatever light you get from stars & off the moon). IR (mostly thermal energy) is usually quite abundant, though.
Got any references?
=Smidge=
What the article didn't mention is that this material could be the killer app for orbital manufacturing. The value of the cells would justify lofting the raw metals into space to form into enormous panels in the open vacuum, free of contaminants. Solar cells with 50% efficiency would compete economically against fossil fuels.
When the article mentioned being able to absorb near infrared light, I was reminded of my ridiculous idea to violate the laws of thermodynamics. Basically, you would need a solar cell that would generate power from infrared light. Use this solar cell to power a battery recharging unit. Place an uncharged battery into the unit, and put it in a dark closet for a year. At room temperature, objects should be giving off black body radiation in the infrared spectrum, so the wall of the closet should be emitting trace amounts of infrared light. So, with enough time, the trickle of current should recharge the battery. Therefore, I have taken heat energy, which is very entropic, and confined it to a battery, thereby decreasing the entropy of the system without expending energy to do it. I know this can't work, but I'm having trouble seeing why. Any ideas?
You're still converting one form of energy into another. That infrared would otherwise be radiating to other objects, increasing their entropy. The infrared produced is tiny compared to the total entropy of the object radiating it, so you could look at it as absorbing the small amount of spontaneous order generated from chaos.
In addition, as I said in the subject, light is light. If one frequency of light can be turned into energy, they all ought to be susceptible to the same concept, if not the same receiver.
Here's a question for you, and for everyone else: Would a solar cell continue to operate in an ambient temperature sufficient to generate that frequency in black-body radiation?
As I understand it, UV light hits the earth at all hours.
Does anyone know how much UV hits the earth during the night?
Almost none. Virtually all of the light that strikes Earth comes from the sun.
As another poster pointed out, you may be confusing this with the mid-IR glow that warm objects (including the ground and the air) give off. The amounts of energy involved are very low, and room-temperature thermal IR is difficult to convert to electricity efficiently.
Any solar power scheme (and so any photovoltaic scheme) has to have enough storage capacity to power the load overnight. Ideally, it should be able to provide power for several days, in case of cloud cover/rain/whatever. This is why most home-powering schemes involve large battery arrays. A city-powering solar plant would probably use fuel cells (energy density is much higher, and there are off-the-shelf models of power-plant scale already available and in use).
Here's a question for you, and for everyone else: Would a solar cell continue to operate in an ambient temperature sufficient to generate that frequency in black-body radiation?
I *think* the answer is "no", as thermal energy would cause current to flow both ways across the junction you're trying to use to generate power, but as this is not my area of expertise, I could easily be wrong.
Question: How do you make President Bush and his "real" constituency soil their adult diapers? Answer: Have them read the article! To the article authors: Hire some body guards! BTW: You have to wonder how much energy (initially) it would require to manufacture, say, a modest 100 kW solar power plant and the amounts of pollution that manufacturing process would produce. I guess, eventually, with enough solar power plants humming away, providing enough energy to manufacture other solar power plants, this question would be academic.
For utility/residential applications, efficiency isn't very important since there's LOTS of roof area... you can use relatively inefficient technology. What really matters is $/Watt. How much do I have to spend to generate energy equivalent my house's usage?
~gb
The article noted that current-best solar cells are about 25% efficient, vs. 30% max. theoretical. How many percent more efficient are you figuring on the new solar cells being if space-made (vs. Earth-made)?
Check out the $billions$ that the dinky space station costs just to keep up. Ditto launch costs for your raw materials & totally unproven zero-grav solar cell factory equipment.
Now spread the extra costs of space-made solar cells out over the number of cells that you think will actually pass QC & reentry. Where do you see the high-volume market willing to pay the $HUGE$ price premium for a few percent better efficiency?
As gbell notes further down, efficiency doesn't mean too much, especially competing against fossil fuels. Cost per watt (call it financial efficiency) is what really matters.
It's easy to make up & spread cool- and credible-sounding stuff. Finding & checking hard facts is hard work.
Heinlein described in one of his short stories how some guy using nano-crystals to create the ultimate "cold light source" and noticing that, like most physical processes, this one is works in reverse as well - he's just invented the "perfect" solar collector! Of course the technical specifics are wrong, he got even them pretty close, and he got the basic idea right...
I also loved how he threw in "small" inventions with thought-out consequences into his stories as background. There's a scene I'll always remember where a young cadet-wannabe facing testing answers his father's call on the cell phone while his friend smirks "I tricked my parents - packed the phone in my bags". I bet this scene is replayed with variants all over the world by now. Pretty good for a story written in the 50s or 60s.
Now, where's my budget rental spaceship he was so derogatory about?
What about the rest of the EM spectrum. If electricity could be gotten from that, it would be even better.
Not by much. Most of the energy emitted by a hot object is near the peak of the black-body curve. The sun's surface is hot enough to put this well into the visible range (and enough of it beyond that range to give beachgoers a nasty sunburn). If you can process everything from near-IR to near-UV (or farther), you've got almost all of it.
I don't know if that's the same story or not, but I was remembering one where two scientists invent a full-spectrum solar cell, and the only way they can get it into the world without getting themselves murdered first, is to publish the specs openly and then collect royalties.
:)
Heinlein - he da man!
As an aside, a much more feasible way of vastly reducing our dependency on fossil fuels would be to switch everything feasible over to biodiesel. A lot less pollution, too, as well as better fuel efficiency than gasoline engines, plus the engines are simpler and last longer than gasoline engines (no spark system - diesel engines ignite during the compression process - no spark plugs, etc. needed).
Do a Google search for 'biodiesel' and enlighten yourself.
There was article a little while ago about how they had created a new tungston crystal configuration that would adsorb radiation in a certain spectrum and re-emitt at another. In that case they were adsorbing infrared and re-emitting at visible to wildly increase the efficency of incandencent lights, but IIRC the article said that it could be tuned to a wide range of spectra.
What is keeping them from using this to adsorb the visible spectrum and re-emit at an effecient spectrum from converting to electricity ?
Im not here now... Im out KILLING pepperoni
current commericial solar cell designs actually absorb a large frequency range of the sun's EM energy; little is reflected unless the angle of incidence is oblique enough. the issue is that only a certain frequency range can push electrons into the conduction layer of the material (i.e. produce electricity). the remainder of this absorbed energy will mostly increase the amount of heat in the material. this heat will either be conducted away or be re-radiated as longer wavelength photons.
What the article doesn't happen to mention is that InAs (Indium Arsenide) was believed to have a bandgap around 1.6eV (not sure the exact number) and it's now known to be somewhere in the range of ~0.6eV. The article also don't mention phosphide compounds, which are far bigger in research and industry right now.
Fact is, nitrides are bastards to grow. You have to use gas-sources (instead of solid sources that most MBE-ers prefer). There's also no current way to make a nitride-based substrate, which means growing (typically) on sapphire or other lattice mis-matched substrates (GaAs, InP, etc). These lead to HUGE dislocation densities that greatly impact performace.
Now, that doesn't mean this can't be done. And in fact, magic is being done all the time in the world of research. But nitrides aren't going to be realized for some time. Not at least until other technologies pan out first (phosphides and the like). Those are cheaper to grow and allow for much lower defect densities.
Just so you folk's know I'm not just talking out of my ars--do some research and look up some papers. Authors to look for are Steve Ringel (OSU), Gene Fitzgerald (MIT), John Carlin (OSU), Sumitomo (Japan, somewhere), and by-far Yamaguchi (Toyota Technological Institute). Read up on these folks' work and those around them--they know space-based photovoltaics better than most, and very, very, very, very few are working with nitrides right now. Not that it's not going to eventually happen--but until defect densities get low enough, there's simply no way to make a good solar cell (read up on the previous authors' works if you want the theoretical calculations as to why).
Long, cute, or funny Sigs are just another form of over compensation, used by geeks, nerdz, etc.
This is an interesting twist on the subject!
The answer is no, as suggested by the Second Law. To see why, you need an account of how solar cells actually work.
Infalling light is absorbed by the material, by dislodging electrons either from a bound orbit, or a semi-free state like a metallic subtrate or semiconductor. The electron absorbs the photon, re-emitting some of the light as another, lower frequency photon, and taking some of the the momentum and energy with it. The new energy and momentum is sufficient to transport it over a potential barrier to the other side of a layered semiconductor or similar. (All semiconductors are layered -- typically they upper few micrometers are doped, wheras lower down it has a different composition).
The solar cell's composition is such that the electron moves up a potential hill, over the brow, and sits in a dip at the top (on the other side of the solar cell). From there, it can get down the hill again (lose it's energy) either by getting over the brow again, or by travelling down the handy attached wires and charging a battery (say).
Imagine if the back of the cell was transparent, and also exposed to sunlight: Then the sunlight falling on that side would knock electrons down the hill as well! This would actually happen EVEN MORE because the work needed to get over the brow out of the little dip at the top is much smaller than the work needed to get all the way up the hill. The difference is that you can't make the electron do any useful work if it is already at the bottom of the hill.
Now if the solar cell is at the same temperature as the black body radiation, the (usually metal or glass) substrate on which the cell is mounted will emit black body radiation too. By the same argument, the equal amount of infalling light from the back of the cell will result in at least as many electrons being knocked down the hill as are being knocked up the hill by the infalling light you want to do the work.
Upshot: The back of the solar cell must be cooler than the temperature of the infalling radiation for it to work.
To clear up a last couple of points: If the back of the cell is not a black-body emitter, it will either be partially transparent or partially reflective or both. There are no other alternatives (because of the quantum symmetries involved). If it is partially transparent, then the temperature of the objects behind the solar cell becomes relevant. If it is partially reflective, the difference is made up by the reflected heat not absorbed by the solar cell -- including the black body radiation of the cell semiconductor if it is not transparent, or the infalling light if it is.
NO ID: BEING FREE MEANS NOT HAVING TO PROVE IT
RTFA. 30% is max efficiency for single-layer cells. Multi-layered cells can get up to 75%.
Now spread the extra costs of space-made solar cells out over the number of cells that you think will actually pass QC & reentry. Where do you see the high-volume market willing to pay the $HUGE$ price premium for a few percent better efficiency?
I thought the original poster was talking about manufacturing panels in space, for use in space.
As gbell notes further down, efficiency doesn't mean too much, especially competing against fossil fuels. Cost per watt (call it financial efficiency) is what really matters.
True, but unless the cost of manufacture scales up faster than the efficiency, this is a win by both criteria.
My deviantArt site
I read the article...you're missing my point. It doesn't matter if the new cells can get 95% efficient - i'm looking at the SPREAD in efficiency between "Made on Earth" and "Made in Space" cells. There is just plain NO WAY that "Made in Space"'s small efficiency boost can justify the MUCH larger cost of manufacture in orbit.
Making panels in space for use in space is interesting...but hard to reconcile with his comment about competing with fossil fuels. Burning fossil fuels for electricity in space has been rather unpopular & uneconomical for quite a few years now.
I don't think this is about (cool idea) large-scale generation of electricity in space to be beamed down to Earth. Nothing i've seen suggests that efficiency of full-spectrum solar cells has anything to do with why that idea isn't flying.
It's easy to make up & spread cool- and credible-sounding stuff. Finding & checking hard facts is hard work.
Solar energy: Cheap, clean hope for tomorrow.
Suit: "So this stuff really works?"
Hans Moleman: "It certainly does."
Suit: "Oh, well, lotsa luck!" *whack*
Biodiesel, dude, BIOdiesel - very different from diesel.
Just a thought. I wonder if it's reasonable to pump water to elevated storage and use this as overnight power. Overnight power needs are MUCH less than peak day time needs.
You could, but energy density is extremely low (a few tens of joules per kilogram for something you could install in your backyard, vs. tens of megajoules per kilogram for fuel cells or hundreds of kilojoules per kilogram for batteries). The plumbing and storage itself is cheap, but the pump/generator will probably cost more than batteries and a power converter would.
(a clip from an EPA report):
The Environmental Protection Agency (EPA) has released a new
comprehensive technical report of biodiesel emissions data that shows biodiesel use can reduce
emissions of particulate matter by 47 percent when compared to petroleum diesel in unmodified
diesel engines. The report also verified a 67 percent reduction in unburned hydrocarbons and a
48 percent reduction in carbon monoxide with pure biodiesel (B100).