Dr. Tierney is an expert on energy policy and economics, specializing in the electric and gas industries. She has consulted to companies, governments, non-profits, and other organizations on energy markets, as well as economic and environmental regulation and strategy. Her expert witness and business consulting services have involved industry restructuring, market analyses, clean energy regulatory policies, transmission issues, wholesale and retail market design, and resource planning and procurement.

Dr. Tierney is a former Assistant Secretary for Policy at the U.S. Department of Energy, state cabinet officer for environmental affairs, and state public utility commissioner; she chairs the External Advisory Board of the National Renewable Energy Laboratory, is a director of the World Resources Institute, and serves on other boards. She has published widely, and frequently speaks at industry conferences.