Prototype of a 20 kW cogenerator with reduced global cost

The paper discusses the project, design and overall performance of a high efficiency microcogenerator prototype of 20 kW of electric power and about 40 kW of thermal power, suitable for small industrial or residential grid-connected applications, fuelled by natural gas or LPG. This unit has been conceived specifically as a local integrated energy platform having in durability, high global efficiency and cost reduction the most important goals to be achieved. Nowadays there are several plants with medium power microcogeneration systems (i.e. around 20 kWe) available on the market, most of them motored by internal combustion engines, which can show very high electric performances (between 30% and 35% of efficiency) and a P.E.R. (Primary Energy Ratio, i.e. the energy utilization rate of fuel) between 85% and 95%. However these systems result still expensive and bulky, making the investment unsuitable in most cases. In order to solve the above evidenced problems the plant prototype presented in the paper was conceived since the beginning as a low cost system, as it is based on a wide spread Diesel light trucks engine which has been converted into a spark ignition unit by Istituto Motori CNR of Italy in a very inexpensive way. At the same time the generation system was chosen to reduce the global cost, so that a common low cost air cooled induction motor has been selected among many other units. A new design regarding containing case has been adopted, in order to perfectly isolate the internal combustion engine and other hot elements, leaving on the external side just the air cooled generator. Always with the aim of reducing manufacturing cost, the whole plant was put up just adopting reliable and cost effective commercial components. In the paper are reported the most significant results regarding global efficiency and emissions when fed with natural gas, showing that this kind of plants could be considered an immediate solution for a very high efficiency electric and - hermal production together with an important reduction of plant cost.