The researchers tested how much of the light emitted by the dye makes it to the edges of 10-centimeter squares of coated glass, the largest allowed by their laboratory equipment. Based on their measurements, they project that they can make solar concentrators large enough to bring down the costs of solar power to near that of conventional electricity, given expected reductions in the cost of solar cells. “We showed much bigger concentration factors than people had shown before,” Baldo says.
The researchers also tested an inexpensive way to improve the efficiency of solar cells by capturing more of the energy in sunlight. Each wavelength of light, or color, has a different amount of energy. Infrared photons have the least energy, and ultraviolet photons have the most. Different types of semiconductor materials are best for different wavelengths. It’s possible to build more than one type of solar cell into a single module, but this can be more expensive than it’s worth.
The dye-coated glass sheets provide a cheap way to use more than one type of solar cell in a single solar module–one solar cell tuned to work with low-energy light, and the other to work with high-energy light. Two glass sheets are stacked. The top one absorbs high-energy light and channels it to a small solar cell matched to that light. The other captures lower-energy photons and channels those to another solar cell. Based on the researchers’ initial results, Baldo says, “you can almost double the efficiency of your overall system if you do this.”
The researchers still need to make bigger concentrators to test their predictions. They are also working to improve the quality of the dyes, including the range of colors that they can absorb. Baldo and his colleagues have founded a company–Covalent Solar, based in Cambridge, MA–to bring the technology to market within three years. Jerry Olson, an expert in solar concentrators at the National Renewable Energy Laboratory, in Golden, CO, says that the work represents some “good steps forward.” But, adds Olson, “time will tell if the projections come true.”