The cogeneration, or the combined production of electric and/or mechanical and thermal energy, is a well-established technology now, which has important environmental benefits and has been noted by the European Community as one of the first elements to save primary energy, to avoid network losses and to reduce the greenhouse gas emissions. In particular, our interest will be focused on the micro-cogeneration, MCHP (electric power <= 15 kW), which represents a valid and interesting application of this technology which refers, above all, to residential and light commercial users [M. Dentice d'Accadia, M. Sasso, S. Sibilio, Cogeneration for energy saving in household applications, in: P. Bertoldi, A. Ricci, A. de Almeida (Eds.), Energy Efficiency in Household Appliances and Lighting, Springer, Berlin, 2001, pp. 210-221; Directive 2004/8/EC of the European Parliament and of the Council of the 11 February 2004 on the promotion of cogeneration based on the useful heat demand in the internal energy market and amending Directive 92/42/EEC, Official Journal of the European Union (2004)]. In particular, our work group started a R&D programme on micro-cogeneration in 1995: a laboratory, equipped with the most common appliances (washing-machine, dishwasher, storage water heater,...), has been built and some MCHP prototypes have been tested too. In this article, the results of an intense experimental activity on three different micro-cogenerators, one of them made in Japan and in a pre-selling phase, are reported. In a previous paper a detailed analysis of the test facility, with the description of the equipments and the data acquisition systems, can be found [M. Dentice, d'Accadia, M. Sasso, S. Sibilio, R. Vanoli, Micro-combined heat and power in residential and light commercial applications, Applied Thermal Engineering 23 (2003) 1247-1259]. A typical 3-E (Energetic, Economic and Environmental) approach has been performed to compare the proposed energy system, MCHP, to the conventional one based on separate "production". In the energetic analysis the amount of primary energy savings provided by micro-cogeneration unit has been evaluated for different types of MCHP units and at various working conditions. Furthermore the evaluation of the equivalent CO, emissions of the compared systems, MCHP and conventional systems, allows to calculate the MCHP potentials to reduce greenhouse gas emissions. Finally the Simple Pay Back approach has been considered to define the economic feasibility of cogeneration in small size applications with the varying of some economic variables (first cost, gas price, operating hours per year...). (C) 2006 Elsevier B.V. All rights reserved.