An efficient small-power cogeneration-unit suitable for residential off-grid application

The paper deals with the design of a prototype of a small microcogeneration unit of about 2 kW electric power and about 5 kW thermal power, suitable for residential off grid applications, designed and developed at Istituto Motori CNR of Italy. This unit has been conceived specifically as a recharging system for energy conversion system for houses, having in low noise and vibration, durability and a high global efficiency the most important goals to be achieved. The paper first defines the state of the art of small power microcogeneration units and then the ratio which led to the adoption of a single cylinder, vertical crankshaft, internal combustion engine which has been derived from an outboard motor unit (characterized by a robust construction and high reliability), in order to produce the above mentioned electric and thermal power. Then, an explanation of the main design characteristics of the system is given, with a discussion over every modified and/or new designed element, made to obtain an higher electric efficiency and durability, lower emissions and reduce, at the same time, the cost coming from new design and manufacture. The micro-cogenerator has been tested in its two main elements, i.e. the electric generator (derived from a permanent magnet hub-motor, commonly adopted on electric scooters) and the internal combustion engine. Finally a complete running test of the whole equipment has been carried out, in order to evaluate the effective electric and thermal efficiency.