Sites first came to campus in 1971. Just a few years after arriving at CSU, he became interested in the growing field of photovoltaics. With colleagues, Sites began investigating various thin-film materials for their light-to-energy conversion properties, eventually specializing in characterization and performance of photovoltaic materials made from cadmium telluride. He and collaborators have been supported by millions in federal research grants over his career, most recently a $3.5 million grant from the Department of Energy for investigating improvements in the back contact of cadmium telluride solar cells.