Glass Solar Cell Concentrators Eliminate Need to Track Sun

The Massachusetts Institute of Technology (MIT) of the US has developed a light concentration system for solar cells that does not track the sun. The method can utilize display glass and even window glass in homes, office buildings, etc, as sunlight concentrators. In addition, said a source at MIT, it makes it possible to drop the cost of the solar cell system to a tenth or less.

The new concentrator has no lenses, merely using a light guide (Fig 1a). It consists of an organic thinfilm with fluorescent or phosphorescent emission properties placed on a sheet of glass with a high refractive index of about 1.8. Light enters the light guide, and only light of a specific wavelength is absorbed by the organic material, which emits light of a slightly longer wavelength. This emitted light travels inside the glass and is collected at the edges. If solar cells are placed at window edges it would be possible (theoretically) to use small solar cells to generate the same amount of electrical energy as a solar cell of the same area as the light guide. The concentration function of the light guide is not affected by the angle of incidence, making tracking mechanisms unnecessary.

Solar cells using the same idea were first prototyped in the late 1970s, but the efficiency of the light guide was only about 1%, preventing adequate concentration efficiency. The effective efficiency of the newly developed solution is between 10 and 61 times higher than the solar cell area. A source at MIT said the improvement is due to a better understanding of organic materials, improved film growth technology and other factors.

Only the light guide has been fabricated at present, and measurements of performance when mated to an actual solar cell are scheduled for the future. Estimates of performance changes to variation in light guide size are based on simulation results.