Posted on 11/25/2008 12:19:00 AM PST by neverdem
New ways of squeezing out greater efficiency from solar photovoltaic cells are emerging from computer simulations and lab tests conducted by a team of physicists and engineers at MIT.
Using computer modeling and a variety of advanced chip-manufacturing techniques, they have applied an antireflection coating to the front, and a novel combination of multi-layered reflective coatings and a tightly spaced array of lines — called a diffraction grating — to the backs of ultrathin silicon films to boost the cells’ output by as much as 50 percent.
The carefully designed layers deposited on the back of the cell cause the light to bounce around longer inside the thin silicon layer, giving it time to deposit its energy and produce an electric current. Without these coatings, light would just be reflected back out into the surrounding air, said Peter Bermel, a postdoctoral researcher in MIT’s physics department who has been working on the project.
“It’s critical to ensure that any light that enters the layer travels through a long path in the silicon,” Bermel said. “The issue is how far does light have to travel [in the silicon] before there’s a high probability of being absorbed” and knocking loose electrons to produce an electric current.
The team began by running thousands of computer simulations in which they tried out variations in the spacing of lines in the grid, the thickness of the silicon and the number and thicknesses of reflective layers deposited on the back surface. “We use our simulation tools to optimize overall efficiency and maximize the power coming out,” Bermel said.
“The simulated performance was remarkably better than any other structure, promising, for 2-micrometer-thick films, a 50 percent efficiency increase in conversion of sunlight to electricity,” said Lionel Kimerling, the Thomas Lord Professor of Materials Science and Engineering, who directed the project.
The simulations were then validated by actual lab-scale tests. “The final and most important ingredient was the relentless dedication of graduate student Lirong Zeng, in the Department of Materials Science and Engineering, to refining the structure and making it,” Kimerling said. “The experiments confirmed the predictions, and the results have drawn considerable industry interest.”
The team will report the first reduction to practice of their findings on Dec. 2 at the Materials Research Society’s annual meeting in Boston. A paper on their findings has been accepted for publication in Applied Physics Letters.
The work is just a first step toward actually producing a commercially viable, improved solar cell. That will require additional fine-tuning through continuing simulations and lab tests, and then more work on the manufacturing processes and materials. “If the solar business stays strong,” Kimerling said, “implementation within the next three years is possible.”
The MIT Deshpande Center selected the project for an “i-team” study to evaluate its business potential. The team analyzed the potential impact of this efficient thin solar cell technology and found significant benefits in both manufacturing and electrical power delivery, for applications ranging from remote off-grid to dedicated clean power.
And the potential for savings is great, because the high-quality silicon crystal substrates used in conventional solar cells represent about half the cost, and the thin films in this version use only about 1 percent as much silicon, Bermel said.
This project, along with other research work going on now in solar cells, has the potential to get costs down “so that it becomes competitive with grid electricity,” Bermel said. While no single project is likely to achieve that goal, he said, this work is “the kind of science that needs to be explored in order to achieve that.”
In addition to Kimerling, Bermel and Zeng, the work was done by John Joannopoulos, the Francis Wright Davis Professor of Physics, and by research engineer Bernard A. Alamariu, research specialist Kurt A. Broderick, both of the Microsystems Technology Laboratories; postdoctoral associate Jifeng Liu; Ching-yin Hong and research associate Xiaoman Duan, both of the Materials Processing Center. Funding was provided by the Thomas Lord Chair in Materials Science and Engineering, the MIT-MIST Initiative, the Materials Research Science and Engineering Center Program of the NSF and the Army Research Office through the Institute for Soldier Nanotechnologies.
so then if more of the suns heat is trapped into the solar cell as opposed to reflecting from the earth and back out to space, then are solar cells really prevent the planet from global warming?
Heh never mind. At least someone did!
Good news all round I would think.
I saw a show recently on either Nat Geo, or The Science Channel that was all about "alternative Green" energy.
IIRC, when the show talked about "solar energy", it was shown that as long as "solar cells have been around (say at least 20-30 years) that the come from somewhere in Europe, and that they have managed to get a solar cell that ACTUALLY can gather and use up to and astonashing EIGHTTEEN PERCENT of the sun's energy that hits it!!!!!!!!!
Hmmm....so if these folks have increased that 18% by 50%........WOW boys and girls!!!! We've managed in 30 years to finally get a solar cell to use almost 28% of the frickin' sun's energy that hits it!!!!!!!!!
NOW I know why the dems don't wanna bother drillin' no place!!!!!!!!!!!
How many of these cells will it take to power my 8500 BTU
air cinditioner?
I live in the mid west sun only appear every now and then.
Do you know how much havoc it can cause to suck nearly 30% of the available solar energy out of the climate sustem?
DOOOoooooom!
We must ban solar NOW....
We’ve already done in oil; coal nearly so; nukes is dead; wind kills bats & birds, and causes imaginary syndromes....
Yah-hah-ha! We’ll have these capitlist creeps back in caves eating raw veggies before they know waht hit’m, boys!
IIRC, you like this stuff.
"I live in the mid west sun only appear every now and then."
Just one.
(...but it will probably have to be the size of the WHOLE mid-west...)
Only in the computer.
Actual manufacturing costs would increase 1500%.
yitbos
:}
Well let’s say it is 28% efficient (I don’t know what it really is). Here in central California the sun’s energy is about 720 watts per square meter on average for 6 hours a day in the summer. 28% of that is about 202 watts generated per square meter for 6 hours a day. So that’s about 1.21 kWh of electricity per day per square meter.
That 8500 BTU air conditioner should take about 950 watts to operate depending on its efficiency. If it is on (that is actually running) approximately 20% of the day it should take about 4.56 kWh of electricity each day.
Therefore it would take about 4.2 square meters (or a little less than 7 feet by 7 feet) of these cells to generate the needed energy to power a 8500 BTU air conditioner including a 10% loss getting from DC to AC.
And the sun shines for more than 6 hours a day here.
Actually, these are thin-film photovoltaics and the thin-film solutions are only in the 8%-12% efficiency range. Those using polysilicon are in the high-teens with the best being from SunPower at 22%-23%. Poly versus thin-films are apples & oranges!
ping for later
Solar power is, and always will be, a supplement to existing energy sources. As long as that limitation is realised, an increase to 28% efficiency is great news. It isnt going to solve the energy crisis, not by any means, but it might ease it a bit.
This is great newz for General Motors! — after their bailout, when Congress is designing the cars they have to build, then their solar-powered car that no one wants to buy, will go an extra 10 feet before sputtering to a stop.
And I can’t wait for the Tahoe powered by a windmill on the roof. That will be really bitchin!
Thanks!
Do you still have the renewable energy ping list?
Please Freep Mail me if you'd like on/off
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