Second, Stion’s panels are tuned to efficiently convert different parts of the solar spectrum than other CIGS panels. Its first-generation product is tuned absorb light more toward the red end of the solar spectrum, which makes it a good match with a solar cell—made of materials similar to CIGS—designed for the blue end of the spectrum.
Pairing the cells increases the overall solar-panel efficiency and can drive down costs by reducing the number of panels that need to be installed. (Tandem thin-film solar cells made of amorphous silicon have been made by other manufacturers, but they are far less efficient than the ones Stion is developing.)
Stion, which was founded in 2006, has raised about $115 million to date. It makes solar panels in San Jose, California, and is building another factory in Mississippi with the help of an additional $75 million loan. Its goal under the NREL funding is to produce, within a year, a version of its tandem panels that could be mass-produced.
The NREL program is meant to fund companies that are taking “radically different” approaches to solar panels that could lead to the production of solar panels at “below 50 cents per watt,” says Martha Symko-Davies, who manages the PV Technology Incubator project at NREL. Researchers have experimented with CIGS solar cells for decades, but she says companies such as Stion have made great strides in the last three to four years in bringing CIGS to market. As a result, making a tandem cell should now be relatively easy. “If you’ve got your CIGS working, doing what Stion is doing shouldn’t take much more,” she says.