Combined heat and power generationDecisive for the economic efficiency: The annual load duration curve

The economic viability of combined heat and power generation is usually determined by the demand from heat users. This means that cogeneration (CHP) plants should be able to emit useful heat for at least 5,500 hours a year. CHP plants are designed in accordance with the annual load duration curve (orange line above). With this calculation process, the heat requirements of users are categorised according to frequency across all 8,760 hours in a year. Maximum heat is required during just a few hours in winter. The area under the curve corresponds to the annual heating requirement. CHP plants are based on the base heat load – the lowest part of the curve. Their output must remain completely under the curve if at all possible in order to be economic. For peak loads, conventional boilers must be connected.