In heating systems, the primary energy source is converted into heat. In contrast to this, combined heat and power generation (CHP) produces both heat and electricity in the one independent appliance. By using the primary energy source economically in this way, cogeneration of heat and electricity not only contributes to an overall reduction in energy consumption, but it also contributes directly to the protection of the environment. That is why there is active state support for combined heat and power generation. In addition, there are special payments for any unused electricity that is fed into the national grid.
As far as the basic technology is concerned, a distinction is to be drawn between internal and external combustion engines (Otto engines and Stirling engines), steam expansion engines and fuel cells. Combustion engines and steam expansion engines represent the current state of the art in terms of technology. Stirling engines, like fuel cells, are currently undergoing trials. The fuel used, such as natural gas or heating oil, drives a combustion engine with a power generator coupled to it, thus producing electricity. In future, it is entirely conceivable that renewable energy sources such as biogas, vegetable oil, wood pellets and indeed bio-ethanol will be able to be used. The process heat released by the motor is used for space heating and for domestic hot water. The electricity produced is used as required and any excess power fed into the national grid. Decentralised cogeneration of heat and power is a highly efficient way of supplying both space heating and electricity.
Consumers have a choice of different CHP solutions, from outputs of just a few kW to several hundred MW. Whilst so-called “micro-CHP” units with power outputs of up to 5 kWel are used for detached and semi-detached houses, “mini-CHP” units of up to 50 kWel have been developed for small apartment blocks and business premises. No district heating network is required for these smaller CHP units. Industrial premises and also larger housing estates, hospitals and schools use larger CHP units or block cogeneration plants with outputs starting at around 50 kWel. In these applications, CHP systems can supply up to 100 % of the heat and 80 % of a building’s power requirements; moreover, CO2 emissions can be reduced by up to 40 %. In future a large number of block cogeneration plants working together as a “virtual power station” will help smooth out voltage fluctuations in the public power supply.
