Conventionally, power and heat are supplied from separate generation cycles. Electricity is produced in large-scale centralised power plants and supplied to the customer via the grid. Heat is mainly produced in decentralised heating boilers and utilised on-site. During the electricity generation process, thermal power plants emit large quantities of waste heat, which frequently remains unused. This waste heat from central power plants can be used to cover nearby heating or cooling demands by means of district heating or cooling networks. Alternatively – and as used in most countries – cogeneration produces power and heat at the consumer’s premises. The decentralised on-site process thereby serves the client’s heat and, at the same time, electricity demand.
Cogen/trigen applications are ideally suited for constant load profiles of heating and/or cooling energy and electricity. Since the simultaneous generation process on-site minimises energy losses compared to the separate generation and transmission of electricity and heat (and/or cold), cogen reaches aggregate efficiencies as high as 80–95% compared to the efficiency of separate generation processes of about 50%, providing efficiency gains of more than 30% and thus primary energy savings of more than 50%. Thus cogen technologies show significant ecological and also economic advantages (less fuel input and thus reduced greenhouse gas emissions, as well as decreased energy costs for the operator, etc.) compared to the separate production of electric and thermal energy.