This article covers post-prototype fuel cell (FC) systems in stationary or ‘on-site’ applications, for use in non-grid-connected dispersed generation, or grid-connected distributed generation. Both are referred to here as DG. They include a range of sizes from kilowatt to megawatt scale, and may be in combined heat and power (CHP, cogeneration or dual energy use systems), or as electricity-only units. Trigeneration (combined heat, power, and cooling) is a further possibility. The article starts with a general discussion of on-site power systems, and introduces the different types of FC devices for these applications. This is followed by general sections on on-site power systems and their characteristics, and on fuels for DG applications. Sections follow on the subsystems’ aspects of FC systems, and on their scaling characteristics...