>>MIT group turns flat glass into cheap solar concentrator
July 29, 2008, 3:53 pm
Filed under: PV technology

A team from MIT has announced an inexpensive technique for concentrating sunlight on solar cells, using flat glass. Details were reported in the July 11 issue of Science, in an article titled “High-Efficiency Organic Solar Concentrators for Photovoltaics,” by Michael J. Currie, Jonathan K. Mapel, Timothy D. Heidel, Shalom Goffri and Associate Professor Marc A. Baldo.

The team adapted coating techniques developed in lasers and organic light-emitting diodes. A thin coat of organic dye is deposited the upper surface of a glass plate, using a thermal evaporation process. This creates a luminescent solar concentrator (LSC), in which the dye layer absorbs some of the energy of incident photons, allowing the glass to “capture” about 80 percent of the photons coming through. Instead of transmitting straight through the glass, these photons reflect within the glass plate. The plate functions as a wave guide, analogous to fiber-optic cable. Photons are conducted to the edge of the plate, where they meet conventional high-efficiency polysilicon photovoltaic cells bonded in place.

The lab built test units in two layers, with one dye on top to capture short wavelengths and a second plate carrying a dye for long wavelengths. The stack is termed an organic solar concentrator (OSC).

In test panels 10 centimeters square, the team reported a 10-fold increase in power produced by the narrow edge-bound cells. That’s equivalent to a 20-percent boost in power over a conventional PV panel with the same 100-square-centimeter area as the OSC. As the plate grows larger, its area and the number of conducted photos rises geometrically, while the length of the perimeter – and therefore the area of PV cells – rises arithmetically. The larger the plate, the higher the multiplication factor. If the 10-centimeter plate can be said to have a 2.5:1 aspect ratio, a 1-meter plate would have a 25:1 aspect ratio.

The technology raises some interesting possibilities. Because 20 percent of light energy continues through the glass plate, a single-layer OSC could be used to front a solar water-heating panel, or in a window or skylight application, with the PV cells and their wiring protected inside the frame.

The work was sponsored in part by the U.S. Department of Energy’s Office of Science and the National Science Foundation. It will be commercialized by Covalent Solar, launched early this year by authors Mapel, Currie and Goffri. In April, the company won $30,000 in prizes at MIT’s Entrepreneurship Competition.


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