 Barnett was the founder and CEO of solar-cell producer Astropower, Inc.

Barnett graduated from the University of Illinois at Urbana–Champaign in 1963 and earned his doctorate in electrical engineering from Carnegie Mellon University in 1966.He was a fellow of the Institute of Electrical and Electronic Engineers.Barnett joined the University of Delaware (UD) as Director of the Institute of Energy Conversion and Professor of Electrical Engineering.