Massachusetts Institute of Technology (MIT) engineers report a new approach to harnessing the sun's energy that could allow windows to not only provide a clear view and illuminate rooms, but also to use sunlight to efficiently help power the building they are part of.
The work involves the creation of a novel "solar concentrator." "Light is collected over a large area (like a window) and gathered, or concentrated, at the edges," explains Marc A. Baldo, MIT electrical engineering professor.
As a result, rather than covering a roof with expensive solar cells 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.
Solar concentrators in use today "track the sun to generate high optical intensities, often by using large mobile mirrors that are expensive to deploy and maintain," says Baldo and further, "solar cells at the focal point of the mirrors must be cooled, and the entire assembly wastes space around the perimeter to avoid shadowing neighbouring concentrators."
The MIT solar concentrator involves a mixture of two or more dyes that is essentially painted onto a pane of glass or plastic. The dyes work together to absorb light across a range of wavelengths, which is then re-emitted at a different wavelength and transported across the pane to waiting solar cells at the edges.
In the 1970s, similar solar concentrators were developed by impregnating dyes in plastic. But the idea was abandoned because, among other things, not enough of the collected light could reach the edges of the concentrator. Much of it was lost en route.
The MIT engineers, experts in optical techniques developed for lasers and organic light-emitting diodes, realized that perhaps those same advances could be applied to solar concentrators. The result? A mixture of dyes in specific ratios, applied only to the surface of the glass, that allows some level of control over light absorption and emission. "We made it so the light can travel a much longer distance," researchers in the team say. "We were able to substantially reduce light transport losses, resulting in a tenfold increase in the amount of power converted by the solar cells."
For more attend: Energy Harvesting and Storage Europe 2009