In the last decades technological development showed cogeneration as one of the technical solutions able to combine the different and often contrasting requirements of energetic consumptions and environmental effects for energetic conversion processes. Nevertheless, the optimised dimensioning of combined electricity and heat generation plants needs an accurate evaluation of thermal and electrical loads, as well as their interactions. The present paper reports the characterization of heating, cooling and electric consumption of a cogeneration plant feeding the minimetro electrical loads in Perugia (a city transport system moved by a funicular traction) and a district heating/cooling net, by means of absorption machines. The energetic analysis shows that, because of the strong loads variability, the electrical generation system could be employed if the generated power could be modulated. The proposed plant is therefore made by a modular system, with different groups size; the power chocking is obtained simply by excluding part of the modules. It’s showed that the rising of the initial costs could be balanced by the global efficiency of the system, positioning the installation in the area of a medium term investment, with a reasonable payback period.