Co-generation is the combined production of electricity and heat which guarantees significant primary energy savings, compared to separate plants.
Co-generation uses traditional generation systems (i.e. internal combustion engines, steam and gas turbines, combined cycles), where the thermal energy produced is recovered and re-used for purposes different from electricity generation (eg. Industrial uses, district heating, etc.).
The procedures established by the directive 2004/8/CE (DLgl 20/07), through an increase of energy efficiency and through an improvement of the supply safety, have generated, within the internal market, promotion and development of the so-called high efficiency co-generation, based on the demand of useful heat and primary energy's saving, considering specific national situations. To reach those purposes, the directive has defined:
- electric energy specified as co-generative (the so-called co-generation electricity), starting from the demand of useful thermal energy (or heat);
- high efficiency co-generation, considering the Country members recognize a "guarantee of origin" only for the electric energy considered high efficiency co-generation and confer the expected benefits only to the high efficiency co-generation.
Tri-generation is the generation, using only one fuel, of thermal, electric/mechanic and cooling energy. The cooling energy can be produced, as an alternative, through the use:
- of part of the thermal energy recovered in a cooling absortion cycle, based on transformations of the refrigerating fluid, combined with a substance used as absorbing;
- of part of the electric energy produced, for the alimentation of compression refridgerating groups, currently widespread and whose investment, in economic terms, is far more convenient.
The application for utilities is characterized by the presence of the three energy demands which may occur either separately or simultaneously, and the goal of tri-generation is to increase the utilization factor of the system (profitability).