Because we can get them to concentrate. MIT opens new ‘window’ on solar energy

“Light is collected over a large area [like a window] and gathered, or concentrated, at the edges,” explains Marc A. Baldo, leader of the work and the Esther and Harold E. Edgerton Career Development Associate Professor of Electrical Engineering.

As a result, rather than covering a roof with expensive solar cells (the semiconductor devices that transform sunlight into electricity), the cells only need to be around the edges of a flat glass panel. In addition, the focused light increases the electrical power obtained from each solar cell “by a factor of over 40,” Baldo says.

The factor of 40 is in reference to the light collection, not solar cells themselves, i.e. you are collecting 40 times as much light as you’d get from the area of the edge of the sheet — there’s no comparison to what you’d get if the whole sheet were a solar cell. The action of the collector is much like my clipboard, except the dye is on the surface rather than inside the material. The advantages here would be in reducing the area of the solar cells needed, which are presumably much more expensive, and that some light would still be usable on the other side of the collector.