The growing cost for energy production and distribution as well as problems related to environmental pollution have induced an increasing interest in the research of alternative solutions and in particular innovative technologies capable of compromising energy production cost, optimization and guaranteeing environmental sustainability. One of the technologies of increasing interest in recent years is the Organic Rankine Cycle (ORC). These systems are generally suitable for the recovery of low grade heat at low pressure this is a major advantage of the system in terms of safety and management. Furthermore, they enhance simple operation, low maintenance, and the use of a working fluid that is environmentally friendly. This paper presents a comprehensive and current literature overview of microgeneration systems up to 100kWe. A working fluid screening criteria has been discussed taking into account the environmental impact as well as the thermo-physical properties of various potential working fluids. From the analyses it emerges that the fluid most used in installed ORC systems is the R245fa also confirmed by means of a computational code developed for micro-systems of the size range. Components and expander selection has also been examined, the study reveals that the most suitable expander for the applications of these plant size ranges are the scroll for small installations and the vane or screw expanders for larger installations. Finally a detailed list of characteristics of both industrial and experimental prototype application is presented with references to their manufacturers.
