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New Antireflective Coating Enables Near-Perfect Absorption of Light At All Angles in Solar Panels
5 November 2008
Researchers at Rensselaer Polytechnic Institute have developed a new nanoengineered antireflective coating that boosts the amount of sunlight captured by solar panels to near-perfect levels (>96%) and allows those panels to absorb the entire solar spectrum from nearly any angle. The discovery could help enable the wider use of solar power.
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| The nanoengineered coating boosts the amount of sunlight captured by solar panels and allows those panels to absorb the entire spectrum of sunlight from any angle, regardless of the sun’s position in the sky. Credit: Rensselaer/Shawn Lin. Click to enlarge. |
A paper describing the work led by Professor Shawn-Yu Lin is published in the journal Optics Letters.
An untreated silicon solar cell only absorbs 67.4% of sunlight shone upon it. From an economic and efficiency perspective, this unharvested light is wasted potential and a major barrier hampering the proliferation and widespread adoption of solar power.
After a silicon surface was treated with Lin’s new nanoengineered reflective coating, however, the material absorbed 96.21% of sunlight shone upon it. This gain in absorption was consistent across the entire spectrum of sunlight, from UV to visible light and infrared. Lin’s new coating also absorbs sunlight evenly and equally from all angles.
Most surfaces and coatings are designed to absorb light and transmit light from a specific range of angles. This same is true of conventional solar panels, which is why some industrial solar arrays are mechanized to slowly move throughout the day so their panels are perfectly aligned with the sun’s position in the sky. Without this automated movement, the panels would not be optimally positioned and would therefore absorb less sunlight. The tradeoff for this increased efficiency, however, is the energy needed to power the automation system, the cost of upkeeping this system, and the possibility of errors or misalignment.
Typical antireflective coatings are engineered to transmit light of one particular wavelength. Lin’s new coating stacks seven of these layers, one on top of the other, in such a way that each layer enhances the antireflective properties of the layer below it. These additional layers also help to “bend” the flow of sunlight to an angle that augments the coating’s antireflective properties. Each layer not only transmits sunlight, it also helps to capture any light that may have otherwise been reflected off of the layers below it.
The seven layers, each with a height of 50 nanometers to 100 nanometers, are made up of silicon dioxide and titanium dioxide nanorods positioned at an oblique angle. The nanorods were attached to a silicon substrate via chemical vapor disposition, and Lin said the new coating can be affixed to nearly any photovoltaic materials for use in solar cells, including III-V multi-junction and cadmium telluride.
Along with Lin and Kuo, co-authors of the paper include 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.
Funding for the project was provided by the US Department of Energy’s Office of Basic Energy Sciences, as well as the US Air Force Office of Scientific Research.
(A hat-tip to Jeremy!)
Resources
Mei-Ling Kuo, David J. Poxson, Yong Sung Kim, Frank W. Mont, Jong Kyu Kim, E. Fred Schubert, and Shawn-Yu Lin (2008) Realization of a near-perfect antireflection coating for silicon solar energy utilization. Optics Letters, Vol. 33, Issue 21, pp. 2527-2529 doi:10.1364/OL.33.002527
November 5, 2008 in Brief | Permalink | Comments (12) | TrackBack (0)
Comments
Posted by: | November 05, 2008 at 04:38 PM
No mention if this is applicable to the glass cover but If this can be economically marketed, there will be enormous benefits including multipliers in installation.
It would seem the tracker systems may have a hard time justifying their costs.
Posted by: arnold | November 05, 2008 at 05:15 PM
This seems like it would be cool for a money-is-no-object outer space application, but I find it hard to believe that this super-trick nano-rod technology can be done cheaper than just buying 40% more uncoated cells.
Posted by: George | November 05, 2008 at 08:46 PM
I have limited south-facing roof space, so I was looking at installing panels in the 19-21% efficiency range rather than the normal, cheaper 12-14% panels and still couldn't get enough total power. If this optimizes affordable cells up to a 30% efficiency, then all the better for situations like mine. It also means the panels can be laid flat against the roof surface rather than propped up to the optimal angle if aesthetics is an installation issue, even though that will reduce the W/m2 slightly.
Alternatively I could pay a solar farm in Arizona or somewhere really sunny to generate my solar power for me and feed it into the grid there.
Posted by: Floatplane | November 06, 2008 at 01:35 AM
On thing is reflection capability but other thing is light intensity reduction proportionaly per sq. meter to the angle therefore film is solving only half of angle issue.
Posted by: Darius | November 06, 2008 at 04:15 AM
If this coating reduces reflextions, tracking systems would rather be more economic than before. The geometry of just capturing 50% av the sun at 45 degrees angle is central. Even if we can increase the energy uptake at this angle by 50%, it is still 25% less than panels without the coating that are perpendicular to the sun. Think about what a tracked panel with coating would sum up to!
Posted by: Lunken | November 06, 2008 at 04:35 AM
Great news.
All future (and existing ??) solar panels may one day be similary coated to increase output by almost 50%. Would this coating increase the already very high output panels from 30% to 45% ?. If so, solar power will have a great future.
Posted by: HarveyD | November 06, 2008 at 10:01 AM
Solar cells are still too expensive. Most people in the US do not own enough area to generate enough solar energy for their use even if they could afford the solar cells. If you can buy electricity from coal fire power plants, do it and spend your money on an electric car. ..HG..
Posted by: Henry Gibson | November 06, 2008 at 04:43 PM
At present, PV is grid parity in parts of California and in Hawaii. Costs are coming down fast. If thin film breaks out (fingers crossed), the the price per KW installed drops from about the present $4 to less than $1, which would allow massive uptake over a much larger area.
That said, I do think that people do have enough roof area to generate more than enough power for themselves, at least for most of the year and in summer but it would be not cost effective in the more northerly latitudes and cloudy areas. Here's an example of a house solar build in California. Note the impact on the bill and the limited size of the panels.
http://www.extremetech.com/article2/0,2845,2326045,00.asp
Although solar may not compete from a production standpoint in terms of levelized costs, it may on a utility-consumer level as it displaces higher peak power costs that utilities charge customers over the lifetime of the facility. It's how sunEdison makes it money.
Anyway, would like to see a comparison of what the cost and benefits of this technology would add to other solar technologies.
Posted by: aym | November 07, 2008 at 08:41 AM
Quoth Harvey D:
Most people in the US do not own enough area to generate enough solar energy for their use even if they could afford the solar cells.Sorry, Harvey, but you're flat wrong.
The typical household uses about 1 kW average, or 24 kWh/day. If the house has a roof area of 100 m², this is an average of 10 W/m² or 240 Wh/m²/day. Over a year, this is about 88 kWh/m²/yr; if supplied by PV cells at 15% efficiency, this would require 584 kWh/m²/yr of sunlight.
A square meter in mid-Kansas gets about 1550 kWh/m²/yr of sun. This is about 3x the requirement to supply the electricity needed to supply the electricity used by that square meter of house, and if this anti-reflection coating increases the effective efficiency things look even better.
Posted by: Engineer-Poet | November 07, 2008 at 11:04 AM
EP, you quoted Henry Gibson, Not Harvey.
In terms of household 'needs', our home uses less than 10kWhr/day. Energy efficient appliances/HVAC and a conservation mindset are the best ways to realize more independence from energy suppliers.
Posted by: Will S | November 08, 2008 at 08:49 AM
Does this work with concentration pv? Can the coating be put on the lens so that tracking is unnecessary?
Posted by: hmm | November 12, 2008 at 10:38 AM
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this is great but tracking the sun also maximises the normal incident surface of the panel