With one only “fuel” and only one installation, cogeneration allows for simultaneous production of heat and energy. This energy is used to actuate an engine or to heat water (the vapour is used then to actuate a gas turbine then an alternator which is then able to produce electric power). Thus, by recovering thermal energy that is usually lost, the cogeneration process is able to provide these two thermal and electrical energies, with a total output that is significantly higher than that resulting from separate chains.

Moreover, a electricity-heat cogeneration plant operates with steam turbines or gas engines. Natural gas is the primary energy most commonly used to run classic cogeneration plants. Nowadays, however, cogeneration plants tend to use alternative sources of energy, particularly waste or renewable raw materials. Contrary to classic power stations in which the fumes are evacuated directly through the chimney, the cogeneration exhaust fumes are cooled first, yielding their energy to a hot water circuit which is generally transformed into vapour.

All in all, the main difference between cogeneration and traditional thermal electrical or nuclear power stations lies in the method of recovery and the use of the heat produced by cogeneration. In thermal power stations, the vapour turbined to produce electricity is discharged into the natural environment. Cogeneration is thus characterized by an excellent energy efficiency ratio. As opposed to distinct heat and electricity production processes, it saves primary energy. Competitive in comparison to centralized means of production, cogeneration is also valuable in terms of diversification of power production units, and under certain conditions, can avoid electrical supply network costs and losses.

The promotion of combined production of heat and electricity is part of the Community strategy defined within the framework of the resolution of the European Council established on the 8th December 1997. This highlights the fact that cogeneration can contribute to a substantial reduction of the main greenhouse gases, and its aim is to double the total amount of cogenerated energy within the Community by 2010, each Member State being required to take the appropriate measures.

Advantages of cogeneration: Innovative concept/Environmentally-friendly/ Performance /Efficiency.