In a previous companion article, we pointed out that inter-technology synergies will become a generic feature of coming hydrogen age systems. These synergies will develop between sources, currencies and technologies. Unfortunately, today's optimization methodologies, based on energy rather than exergy optics, are often a misleading basis for optimization. To illustrate how the energy and exergy optics give quite startlingly different perceptions, this article uses both approaches to examine a range of technologies from civilization's energy systems, including hydroelectric generating stations at Niagara Falls, a coal-fired electricity generating station and home heating systems. Some observations are provided on how the results apply to fuel cells, which can be used for electricity generation or to cogenerate electricity and heat. The main objectives of this work are to understand better the nature of thermodynamic efficiencies and losses, to see clearly where losses should be attributed, and to more accurately identify how to improve efficiencies. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.