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The new windows will be formed of stacked tinted thin plates of glass which each target a specific wavelength of light, which they gather and emit intensely to cells at their edges.  (Source: Donna Coveney)

An artistic rendition detailing how the new system could easily be applied to existing panels to make them more efficient.  (Source: Nicolle Rager Fuller, NSF)

Marc Baldo, associate professor of electrical engineering and computer science (left), and Shalom Goffri, postdoc in MIT's Research Laboratory of Electronics (right), show off examples of the new solar window layers.  (Source: Donna Coveney)
A new solar design will soon be able to contribute significantly to powering city buildings

There is much ongoing research into making photovoltaic solar power, common among commercial business and residential installations, more efficient.  While many focus on the cells themselves, MIT researchers are focusing on a different approach by changing the places where cells can be deployed and how light gets to them.

MIT researchers built upon previous research into colored dyes from the 1970s and created special glass panels.  Each panel absorbs a different wavelength of light and carries it to solar cells.  The result: the first potentially viable solar windows.

The new research is reported in the July 11 issue of the journal Science.  In it, the researchers detail how the build up their novel "solar concentrator".  Explains Marc A. Baldo, leader of the work and the Esther and Harold E. Edgerton Career Development Associate Professor of Electrical Engineering, "Light is collected over a large area [like a window] and gathered, or concentrated, at the edges."

By clustering solar cells around the edges of the specially prepared sheets of glass, the new method provides a unique alternative to expensive rooftop solar cells.  They are also much more efficient than their rooftop brethren.  The special glass panels concentrate light 40 times standard sunlight before delivery directly to the cell.  Further different designs to absorb different wavelengths are available, so by using windows with several stacked glass panes, absorption can be optimized across the entire visible wavelength.

The system is so simple to manufacturer that the inventors expect it to be deployed within 3 years at little cost over standard window costs.  Furthermore, it can be added to existing solar panels to help concentrate sunlight for virtually no additional cost, and would increase their efficiency by a modest 50 percent, according to the authors.

Baldo's team includes Michael Currie, Jon Mapel, and Timothy Heidel; all graduate students in the Department of Electrical Engineering and Computer Science, and Shalom Goffri, a postdoctoral associate in MIT's Research Laboratory of Electronics.  The U.S. Department of Energy (DOE), a sponsor of the research is very pleased with their progress.

Dr. Aravinda Kini, program manager in the Office of Basic Energy Sciences in the DOE's Office of Science, states, "Professor Baldo's project utilizes innovative design to achieve superior solar conversion without optical tracking.  This accomplishment demonstrates the critical importance of innovative basic research in bringing about revolutionary advances in solar energy utilization in a cost-effective manner."

In the paper, Professor Baldo addresses current methods for improving efficiently, stating that, "track the sun to generate high optical intensities, often by using large mobile mirrors that are expensive to deploy and maintain.  He comments that additionally "solar cells at the focal point of the mirrors must be cooled, and the entire assembly wastes space around the perimeter to avoid shadowing neighboring concentrators."

As he points out, even methods today considered to promote efficiency are clumsy and expensive.  His team's process is extremely simple in comparison with no moving parts.  The windows are painted, in essence, with a series of two dyes.  Combined, the dyes absorb light of a specific wavelength and then retransmit it at the edges of the window. 

The previous work in the 1970s involved a similar principle but lost too much energy during transportation.  The MIT engineers were able to take their expertise in lasers and organic light-emitting diodes and apply it to making a mixture of two special dyes which work much better.  Says Jon Mapel, "We made it so the light can travel a much longer distance.  We were able to substantially reduce light transport losses, resulting in a tenfold increase in the amount of power converted by the solar cells."

The research was sponsored by the National Science Foundation in addition to the DOE.  Professor Baldo is associated with MIT's Research Laboratory of Electronics, Microsystems Technology Laboratories, and Institute for Soldier Nanotechnologies.

Mr. Mapel, Mr. Currie and Mr. Goffri have founded a company Covalent Solar, which looks to make good on the researchers' promise to bring the technology to market within 3 years.  The company is progressing nicely, winning the Energy category ($20,000) and the Audience Judging Award ($10,000) in MIT's $100K Entrepreneurship Competition.  The new design is especially heavy to the tinted-glass heavy urban settings and follows a trend of incorporating wind and solar power into less obtrusive urban-ready designs.



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RE: Sounds intriguing..
By peldor on 7/17/2008 10:45:31 AM , Rating: 2
A vertical plate is a poor orientation for collecting solar power anyway until you get to very high latitudes.


RE: Sounds intriguing..
By Solandri on 7/17/2008 1:32:42 PM , Rating: 2
That's kinda the point of this idea. Surfaces which are poorly oriented are uneconomical for solar collection because right now we plaster the entire surface area with PV cells. This idea is to take something which is much cheaper than PV, cover the surface with it, and put a thin line of PV cells on the edge where it collects the solar energy striking the surface.


RE: Sounds intriguing..
By peldor on 7/17/2008 3:50:08 PM , Rating: 2
It's not like concentrated PV hasn't been done before. If concentrated PV isn't economical now, mounting it at a bad angle isn't a step forward.


RE: Sounds intriguing..
By Solandri on 7/17/2008 3:59:07 PM , Rating: 2
Concentrated PV wasn't economical because you have to move the mirrors on motorized gimbals to track the sun. It might not have been too bad if the sun took the same path through the sky every day, but it doesn't, its path changes with the time of year. The mounting and maintenance costs (and complaints when they pointed the wrong way) got too high.

These are completely passive and immobile.


RE: Sounds intriguing..
By SiliconJon on 7/20/2008 2:03:35 PM , Rating: 2
If the cost were truly low then the cost of a lack of optimized angling could be countered. I have my doubts about the consumer seeing this application done cheaply, if it can be done at all in the near future. But to theorize of the ends rather than the means, if I could purchase power producing windows all around my house for half of what it would cost* to mount a solar panel unit to my roof and the windows produce more than 50% of what the roof unit could produce then it would be a winner of an idea economically, and one hell of a winner aesthetically and maintenance wise.

* This cost being calculated by the difference between installing comparative non-power producing windows, not compared against the cost of not replacing or installing windows.


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