A simple look at the graphs in the figure allows you to understand how contemporary production of electricity and heat at the site of their consumption is convenient if compared to separate and centralized production: the right side shows a typical conversion balance for a cogeneration plant; with 100 units of energy in the form of fuel employed, an average of 38 units of electricity and 45 of heat are obtained. To produce the same quantities separately, an average of 95 units of fuel are needed to get the same amount of electricity from a conventional thermoelectric plant and 53 fuel units to get the same heat from a gas fired boiler.
It is therefore clear that the separate production of electricity and heat requires almost 50% more fuel to provide the same amount of thermal vectors. Additionally, power losses due to Joule heating in transmission and distribution networks can reach up to 10% of the total delivered energy. Thanks to the distributed cogeneration, the heat generated during the process, is almost completely recovered on the site, thus achieving a total efficiency (ratio between the energy actually used and the total energy introduced into the system) close to 90%.