Better solar: In conventional solar cells (a), light (dashed line) enters an antireflective layer (yellow) and then a layer of silicon (green) in which much of the light is converted into electricity. But some of the light (solid arrows) reflects off an aluminum backing, returns through the silicon, and exits without generating electricity. A new material (represented by the dots in [b]) makes it possible to convert more of this light into electricity. Instead of reflecting back out of the solar cell, the light is diffracted by one layer of the material (larger dots). This causes the light to reenter the silicon at a low angle, at which point it bounces around until it is absorbed. The light that makes it through the first layer is reflected by the second layer of material (smaller dots) before being diffracted into the silicon.
Peter Bermel
A new type of material could allow solar cells to harvest far more light.
Much more efficient solar cells may soon be possible as a result of technology that more efficiently captures and uses light. StarSolar, a startup based in Cambridge, MA, aims to capture and use photons that ordinarily pass through solar cells without generating electricity. The company, which is licensing technology developed at MIT, claims that its designs could make it possible to cut the cost of solar cells in half while maintaining high efficiency. This would make solar power about as cheap as electricity from the electric grid.
The effort uses a type of material called a photonic crystal that makes it possible to "do things with light that have never been done before," says John Joannopoulos, a professor of physics at MIT who heads the lab where the new designs for solar applications were developed. Photonic crystals, which can be engineered to reflect and diffract all the photons in specific wavelengths of light, have long been attractive for optical communications, in which the materials can be used to direct and sort light-borne data. Now new manufacturing processes could make the photonic crystals practical for much-larger-scale applications such as photovoltaics.
StarSolar's approach addresses a long-standing challenge in photovoltaics. Silicon, the active material that is used in most solar cells today, has to do double duty. It both absorbs incoming light and converts it into electricity. Solar cells could be cheaper if they used less silicon. If the silicon is made thinner than it is now, it may still retain its ability to convert the photons it absorbs into electricity. But fewer photons will be absorbed, decreasing the efficiency of the cell.
MIT researchers developed sophisticated computer simulations to understand how thin layers of photonic crystal could be engineered to capture and recycle the photons that slip through thin layers of silicon. Silicon easily absorbs blue light, but not red and infrared light. The researchers found that by creating a specific pattern of microscopic spheres of glass within a precisely designed photonic crystal, and then applying this pattern in a thin layer at the back of a solar cell, they could redirect unabsorbed photons back into the silicon.
Today's solar cells already reflect some of the light that passes through the silicon. But the photonic crystal has distinct advantages. Conventional solar cells are backed with a sheet of aluminum. The photonic crystal reflects more light than the aluminum does, especially once the aluminum oxidizes. And the photonic crystal diffracts the light so that it reenters the silicon at a low angle. The low angle prevents the light from escaping the silicon. Instead, it bounces around inside; this increases the chances of the light being absorbed and converted into electricity.
As a result, the photonic crystal can increase the efficiency of solar cells by up to 37 percent, says Peter Bermel, CTO and a cofounder of StarSolar. This makes it possible to use many times less silicon, he says, cutting costs enough to compete with electricity from the grid in many markets. The savings would be especially large now, since a current shortage in refined silicon is keeping solar-cell prices high and slowing the growth of solar-cell production.
In work that could improve solar cells and LEDs, researchers have, for the first time, made practical working devices out of three-dimensional photonic crystals.
Or, eliminate the back reflector, and . . .
you have a skylight that generates electricity.
Imagine: the solar cell is the top pane of a double paned skylight. The "waste" light is transmitted into your home as illumination, so total efficiency is over 50%.
In fact, every window could generate some PV electricity, especially since if UV, which you want to block anyway, is the most efficient band for PV. There are already PV windows in Germany, I think.
Now if we only had a DC standard so that more appliances ran directly off DC electricity, solar would become even more cost-effective . . .
First, it was the Nano-phosphate Lithium Ion battery (suitable for plug-in hybrid electric vehicles, such as the pending Chevrolet Volt),(which, when available in Austin Texas, can be recharged overnight with our City-owned power companies' surplus overnight Wind energy). (Which, according to Management at Austin Energy, our surplus overnight Wind Energy can recharge 130,000 plug-in 40-mile-on-electric Chevy Volt cars with the breakthrough MIT nano-phosphate Lithium Ion Battery technology at $15 of electricity a month!)
Now, it is a stunning improvement in Solar Cell efficiency (at "grid-Kilowatt cost") (WOW!!) as nearly feasible.
This could significantly change everything for the better as well.
MIT really has changed the flavor of the future in that your advancements have changed the environmental outlook to an extremely bright one.
It's all pretty breath-taking.
If only the rest of the country would keep in touch with MIT.
Sincerely, Dan Petit.
innovations in solar with no real outcomes
I'm frustrated about hearing advances in solar technology with no real production cells that are cheap enough for a middle class family to install and fulfill all their electricity needs. The market is there, what's the hold up??!
why can't we install affordable powerful solar cells today on our homes and cars and start moving towards a renewable energy future away from fosil fuels?
Re: innovations in solar with no real outcomes
Agreed with the comment by amakkar. How many consumers are out there "waiting for the other shoe to drop" regarding solar technology. Personally, every time I read about a technology advancement such as this, I think to myself that I should wait on purchasing any PV system. I don't want make a move similar to buying an 8 track player in 1986 or something.
Re: innovations in solar with no real outcomes
This is a company that is looking to bridge that gap...While there is some criticism, it will be interesting to see how they affect the market.
http://www.citizenre.com/web/index.php
http://en.wikipedia.org/wiki/Citizenre
Maybe I'm a little out of left field with this. What about two way mirror for the outer surface? Opaque side out to collect light and reflective side facing toward the reactive surface? Is it too limited opticly to allow light to pass through?
Another thought came to mind what about optical filters? Certain wavelengths of light are prefered but others just bounce out why not only conentrate on blocking those parts of the spectrum that do not help the proccess?
Guest (supert10)
One way mirrors and filters would block to much of the light coming in. There is a way this could be accomplished and it could be retrofited to exiting solar panels. I am trying to find a way to get my concept to researchers without it being stolen. Not very easy to accomplish in todays ultra competive environment. If my idea works it would allow homeowners to buy the current technology without having to worry about it going totally obsolete in a couple of years. It is obvious that the new solar cells are going to be much more effiecent and that makes investing in the old tech very difficult. I think my concept would benifit the emerging solar cells also. It could get very interesting.
However "exciting" the new solar cell technology
being announced may be... It never seems to reach
the consumer, and when it does, through dealers,
etc. there appears to be so many "middlemen" who's
main motive is to make "big bucks" for themselves.
We need a "Wal-Mart" Solar and Wind power company
made available to consumers, to supply these new
forms of energy at a reasonable cost.
We also need all electric power companies to be
forced to accept (meter reversal) private produced
energy back into their power grids.
Wray
Regarding a 'WalMart for windmills and solar PhotoVoltaics', the market is nearly there...
Currently NorthernToolandEquipment , a general purpose mail order supply house , sells a fair selection of small/home windmills , and some small PV battery-charging setups. I do think that WalMart has plans to sell some of this stuff too. Certainly the online marketplace makes homeowner procurement a feasible option.
Your plea highlights a few present shortcommings, though:
I.) The photovoltaics are even more expensive than the windmills [realizing that winmills only have value in areas with a lot of wind!] , and even those are expensive. The supply needs more mature, and mass-scale production , to increase value.
II.) The demand needs more committment , as willingness to invest in alternatives to the extent people invest in , say , their automobiles.
III.) The society needs to gain more experience with deploying/installing these technologies.
n)... In each case , there is a 'chicken-and-egg' problem , we need move forward.
T m.
electrical current must pass through the photonic crystal. If its made of glass beads or whatever, then the photonic crystal will increase the electrical resistance of the cell.
Also, I think that any lithography step will be cost prohibitive. Solar cells are very price sensitive.
Why not just make the back surface nonplanar, which will tend to reduce the angle of reflected light. This can be done without lithography, by etching the silicon with KOH or other anisotropic etachant. This has already been done. Its not in production anywhere that I know of.
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nekote
139 Comments
Combine with Materials That Reflect No Light
Should be combined with the best anti-reflective surface.
As recently highlighted in TR
Materials That Reflect No Light
http://www.technologyreview.com/Nanotech/18265/
Try to keep as many "captured" photons as possible bottled up - continually reflected, until finally absorbed to produce electricity. Kinda' like some demented early style "Pong" electronic game?
Increasing angle of acceptance and / or some sort of sun tracking would be a further boost.
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bmn
75 Comments
Re: Combine with Materials That Reflect No Light
wasn't there some work done a few years back on mass-producible sheets of micro-concentrators??they were intended to enhance angle of acceptance for solar cells to increase yield. wonder if that is another technology that could be combined here to maximize power out.
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