In a combined heat and power plant (CHP), liquid or gaseous fuels, e.g. from a biogas plant, are burnt in a combustion engine.
The procedure is equivalent to combustion in a car or truck engine. A CHP plant is compared to a car engine a stationary engine. It always runs at constant speed without great speed variation, as in a mobile engine of a vehicle. A CHP often has a greater power than a mobile internal combustion engine. The crankshaft in the CHP is connected to a generator. By the rotational motion of the crankshaft electric energy is generated in the generator. Furthermore, heat is recovered from the exhaust gas and from the cooling water circuit.
Such a block heating power plant should reach a high number of operating hours, so that a motor can be operated in the economic area. This area is over 4,500 full load hours of operation per year. There must also be a suitable heat customer so that the heat does not have to be given away into the environment by an emergency cooler.
A modern cogeneration plant achieves an electrical efficiency coefficient of over 45%. By using the waste heat, the overall efficiency is above 90%.