The sun produces an enormous amount of energy. More than 1,000 watts of per square yard hits Earth’s surface every day. Even a tiny amount of that power could meet the energy needs of the entire planet. But solar panels only capture a small percent of that energy. In fact, most commercial solar panels convert just 20 percent of sunlight into electricity. That’s because solar cells are sensitive only to a small portion of the sun’s whole spectrum of light.
Harry Atwater, a physicist at the California Institute of Technology, and his team are working on a solar cell designed to absorb more of that spectrum of light and convert 50 percent of sunlight into electricity. That is huge. It would catapult solar power into the energy limelight, making it affordable and highly competitive with fossil fuels.
There are three designs Atwater’s group is looking at. One of them is a solar panel with a set of metal troughs that contain a series of solar cells, each made of a semiconductor material that responds to a particular wavelengths of light. Optical fibers at the top of the solar cell receive the sunlight first and separate it into its rainbow spectrum, directing those different wavelengths to the appropriate trough and solar cell. (For a nice illustration, see the article from Technology Review.)
Another design would employ optical filters instead of the optical fibers to separate the sunlight into its various wavelengths and a third would use a hologram to split up the spectrum.
Atwater is, ultimately, trying to build better cells using relatively conventional materials and techniques. While it’s possible right now to build solar cells with efficiencies that near 50 percent, those cells are so expensive that the only wide use they have is on spacecraft. That’s way too expensive to get people to put them on their homes. On the other hand, a cheap solar panel that was 50 percent efficient could supply a typical house with the majority of its energy needs — even in the deep winter when there is only a six-hour period of bright sunlight.
Last December, the government agency ARPA-E awarded Atwater and his team $2.4 million to develop the ultra high-efficiency photovoltaics. Let’s hope he can do it.
Credit: Sean Busher/Corbis