Desert Sunlight originated at a time when engineers were just figuring out how to produce s panels, on a mass scale. In the past, panels were often made using which to yield more energy but were expensive and difficult to mass-produce. But First Solar, which is based in Tempe, Ariz., and bought the rights to Desert Sunlight in 20Io, has shied away from silicon and instead pro duces "thin-film" panels made with cad mium telluride, which can be cheaper than silicon but less efficient in convert ing sunlight into energy.