This paper focuses on the critical role of power sources in the future energy economy. It highlights the disruptive nature of the new energy technologies that will come into play, addressing the problems of greenhouse emissions and reduced availability of fossil fuel reserves. The importance of power sources such as fuel cells and batteries is discussed and their inter-relationship with the hydrogen economy explored. Overall it is clear that improved methods of energy storage are of critical importance and these must be optimised both in terms of cost and energy density. There are important challenges to be addressed; however, very positive outcomes can be anticipated. (C) 2004 Elsevier B.V. All rights reserved.