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.