Photos: With solar energy, it's silicon vs. CIGS

CIGS, or copper indium gallium selenide, is being used as the key ingredient in solar panels. Silicon technically is more efficient at harvesting energy from the sun, but CIGS can be printed on flexible sheets. Proponents of the material, such as HelioVolt and Nanosolar, say CIGS can be incorporated into roof tiles and building materials, making the solar technology invisible and the benefits it offers cheap.

In Wales, Shell Solar set up the CIGS-based panels shown in the photo at left. At right, CIGS cells are printed at Nanosolar, a solar-power company based in Palo Alto, Calif.