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The new solar coating, made from a special nanomaterial may not look like much, but it helps solar cells to be 42 percent more efficient, making them close to being cost competitive. Best of all it can be easily produced with existing infrastructure.  (Source: Rensselaer/Shawn Lin)
New coated cell 43 percent more efficient, can be easily produced with current production lines

Solar breakthroughs are relatively commonplace.  However, typically they are iterative -- small increases by a percent or two in efficiency.  Researchers at the Rensselaer Polytechnic Institute have invented a new solar cell that is anything but iterative as it blows away past offerings by a large margin; something RPI calls a "game-changer" for the solar business.

Against relatively cheap coal power, solar -- like nuclear and wind -- has struggled to compete from a purely economic standpoint.  Worse yet, it trails wind and nuclear in terms of how close it is to being cost competitive.  The light at the end of the tunnel is that solar have shown the highest gains in efficiency of any alternative energy source, making its future look very bright.

The new RPI solar cell is a normal cell covered in a special anti-reflective coating which traps sunlight from nearly every angle and part of the spectrum.  The new cell is near perfect; it absorbs 96.21 percent of the sunlight shined on it, while a normal cell could only absorb 67.4 percent.  That 43 percent efficiency boost, coupled with mass production, if properly implemented could place solar on the verge of competing unsubsidized with coal power, at last.

Shawn-Yu Lin, professor of physics at Rensselaer and a member of the university’s Future Chips Constellation describes the breakthrough, stating, "To get maximum efficiency when converting solar power into electricity, you want a solar panel that can absorb nearly every single photon of light, regardless of the sun’s position in the sky.  Our new antireflective coating makes this possible."

Most materials have a mixture of light absorbing (anti-reflective) and light reflecting properties, depending on the angle and wavelength of light.  For example, eyeglasses allow light to pass through on direct angles, but begin to reflect light at sharper angles.  Solar panels in their current form operate with similar mixed character.  In order to improve efficiency, mechanical components must be added to turn to panel to face the sun.  This system entails significant cost and loss of energy efficiency, as well as a great maintenance burden.

With Professor Lin's discovery, the world's first cost-efficient static solar arrays could be produced.  No matter what angle the sun was at, nearly all sunlight would be absorbed and converted to power.  Professor Lin describes, "At the beginning of the project, we asked ‘would it be possible to create a single antireflective structure that can work from all angles?’ Then we attacked the problem from a fundamental perspective, tested and fine-tuned our theory, and created a working device."

Rensselaer physics graduate student Mei-Ling Kuo helped Professor Lin investigate various antireflective coatings.  Their eventual choice was a nanomaterial, consisting of several fine anti-reflective sheets.  Normal antireflective coatings consist of one sheet, which absorbs light at a specific wavelength.  By stacking seven separate layers into a composite coat, they were able to absorb nearly the entire spectrum.  Furthermore, the staggered nature of the layers "bent" the flow of sunlight to a favorable angle, trapping it in the coating.  This means that if light manages to reflect off a lower layer, it will be sent back down by the upper layers.

Each layer was made from a special nanomaterial consisting of silicon dioxide and titanium dioxide nanorods positioned at an oblique angle.  The material was grown through standard chemical vapor deposition techniques, and could be applied to the manufacturing of most standard solar cells, including III-V multi-junction and cadmium telluride cells.

On a microscopic level the nanomaterial looks like a forest of tiny, densely packed trees.  Each layer is 50 nm to 100 nm thick.

The team hopes to bring their technology quickly to market, as it will require little in the way of manufacturing line changes. The research is detailed in the paper "Realization of a Near Perfect Antireflection Coating for Silicon Solar Energy", published in the journal Optics Letters.

Besides Lin and Kuo, the other researchers listed as co-authors on the paper were E. Fred Schubert, Wellfleet Senior Constellation Professor of Future Chips at Rensselaer; Research Assistant Professor Jong Kyu Kim; physics graduate student David Poxson; and electrical engineering graduate student Frank Mont.

The research was funded with the help of funding from the U.S. Department of Energy’s Office of Basic Energy Sciences, as well as the U.S. Air Force Office of Scientific Research.

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RE: so how about actual efficiency?
By Mathos on 11/5/2008 1:24:17 PM , Rating: 2
Yeah but that old efficiency rating was based on only capturing 67% of the available light, part of the time. And due to the need to be mechanized to reach max efficiency very expensive to implement and maintain. You gotta remember though, there are no 100% efficient sources of energy.

Even internal combustion engines are at best 30% efficient in converting gas to power, due to mechanical, heat, other leakage losses. The only advantage to gas is amount of energy produced for the amount of fuel burned.

Coal or natural gas aren't exactly efficient, they lose a great deal of efficiency to mechanical loss and light loss. Though in terms of electricity production the heat energy produced is what is harvested to move the steam turbines.

And to the cloud cover thing. Yeah, cloud cover may cut down on efficiency. But, certain bands of the light spectrum penetrate cloud cover. UV is a major one, as well as infared to a lesser extent. And if they've got the panels able to capture almost 100% of the available light spectrum, that means even during heavy cloud cover they'll still capture light. Night time is always going to be an obvious short coming of solar power. But, a more efficient cost effective solar power system would prove useful, especially in the more arid area's of the world where sunlight is always abundant, as well as areas where the days last 3 months, such as Alaska or the north pole.

Also think of applications such as companies that have large flat buildings, such as factories. They could implement a solar power system on the roof's of the factories, operating of solar energy during the day, and only using conventional electricity at night, or when the output of the solar panels drops below a certain level. It would go a long way to cutting down on the carbon footprint of a lot of industries, due to using less coal power. Would also in time allow them lower overhead cost to run factories. Same could be done for many retail places. I'm sure Wal-Mart would jump on any technology that allowed them to save money by using less conventional electricity.

Not to mention they could also coat electric cars in solar electricity generating materials, allowing to be charged while driving during the day or while idle or parked. Thus, giving them longer drive ranges, and less dependency on a wall outlet or being part of a hybrid system.

RE: so how about actual efficiency?
By FITCamaro on 11/5/08, Rating: 0
RE: so how about actual efficiency?
By Parhel on 11/5/2008 4:06:16 PM , Rating: 2
I would suggest that efficiency isn't a good way to measure the usefulness of solar power technologies. For a combustion engine, the amount of fuel that goes in has an associated cost and a fixed quantity, which is why efficiency is important. For a solar panel, the fuel is free and unlimited. I would instead judge a solar panel on the power output, the size, the cost of production, the availability of the materials needed for production, the average life span, the cost of maintenance, etc. to come up with a cost per watt.

If we were to compare energy options on cost, I would assume that today's best solar panel technology would fall far short of nuclear and fossil fuels. That said, I hope our government continues to invest in solar, so that someday the technology reaches a point where solar makes sense.

RE: so how about actual efficiency?
By Keeir on 11/5/2008 5:26:34 PM , Rating: 2
Efficiency tells you the ratio of Power Output/Power Input. Since Power Input for Solar Power is some constant (depending on location) x size, efficiency ratios can give you a good indication of Power Output/Size. Two of your things to know

RE: so how about actual efficiency?
By Parhel on 11/5/2008 5:35:18 PM , Rating: 2
And I'm sure that's important to certain people, such as engineers incorporating solar panels into their products. But, where it may be useful information when comparing one solar panel to another, it doesn't help one compare solar panels to other energy technologies, such as coal.

By highlandsun on 11/6/2008 7:20:35 AM , Rating: 2
Sure it does, because it tells you how much physical area/land you'll need to match the output of some other given power plant.

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