This paper explores the public's understanding of 'sustainable energy', focusing upon hydrogen, which for most is unfamiliar. We report reactions to a first tour of the recently established 'Hydrogen Research and Demonstration Centre' in the Valleys of South Wales, which was guided by its scientists and engineers. The visitors lived within 50 miles and fell into three age-categories: 14-year old Baccalaureate students; 18-19 year old students at Tertiary College; and adult- members of a Citizens' Panel. They took part in six focus groups which were facilitated, recorded and then analysed thematically by independent sociologists. The paper examines themes on which the groups agreed or disagreed, and how clear or ambiguous their discourse was. While broad consensus was reached on benefits, costs and safety of hydrogen, there were differences in how groups imagined incorporating it into their lives. In conclusion, we draw lessons for securing wider public commitment to sustainable energy. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.