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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: My best guess is that...
By tygrus on 11/5/2008 7:36:25 PM , Rating: 1
Don't need to move panels .. Wrong.
90% effecient panel .. Wrong.

The major reason for decreased energy output when the sun is low is the apparent cross-sectional area of light. Just as shadows are larger in the morning and afternoon, so is the light spread. Use a torch and a flat rubber at the same distance, how much light is blocked when straight on, now rotate the rubber so it is almost end on (as if lit from the sun going down). The rubber blocks less light at high angle (not at 90 deg). You will increase power output by pointing these new panels towards the sun as the sun moves through the day.

Just because you can trap the light doesn't mean you can convert that energy to electricity. May be we can cool the PV panels with water for later use by the hot water service.

How much will these new panels cost per MWh/year (all else being equal) ?

RE: My best guess is that...
By 3DoubleD on 11/5/2008 9:35:58 PM , Rating: 3
Who said anything about a 90% efficient panel. The graded index film has a ~96% collection efficiency (meaning it only reflects ~4%). I clearly said the solar cell efficiency would only marginally go up.

You are correct that trapping the light doesn't mean it will be converted into electricity, but having more available will increase the power output (if thermal issues don't get out of hand, and they won't for a small 22.2% increase in collection efficiency). Water cooling for PVs is a great idea that should be implemented more often. This is a great way to increase the efficiency for a home or business installation. By heating your water from the waste heat generated in the solar cells you can lower your water heating power usage and enjoy increased PV efficiency due to cooler operation. This dramatically increases the efficiency of the system, as does any hybrid implementation in coal or nuclear power plants (nuclear plants see massive efficiency gains when the waste hot water is actually used instead of discarded).

That is true that the cross section of light decreases throughout the day as a function of the sine of the angle for a solar cell that is flat to the ground (sunrise being 0 degrees and sunset being 180 degrees). At larger angles from incidence (early morning, late afternoon) other factors come into play, such as increased scattering and absorption of light in the atmosphere. The power that can be collected during these hours is much smaller than peak daytime hours. Another important factor to consider is that solar cell arrays are used to supplement constant 24 hours power stations (eg coal, nuclear, ect). Peak power demand is during the day, which is normally when the sun is on or near incidence. Solar cells used in this capacity would not require expensive solar tracker motors, greatly enhancing their usefulness.

That said, every situation is different. One would have to do a complete cost analysis of each given situation to see whether it would be worth implementing motorized solar trackers or not. The point was that this brings more options to the table by making the non-motorized arrays more competitive and perhaps opening new markets. Of course this is assuming they can improve the technology to the point where it is practical for solar cell use (which it is not at this moment).

As for the costs, I don't think there is a number yet as this new graded index material isn't ready for practical use as it isn't durable enough. Depending on how those problems are addressed and the methods used to grow the film, it could be close to the cost of current AR coatings or much more. Only time will tell.

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