Combined heat and power plant

A combined heat and power plant (CHP) is a plant for the production of electrical energy and heat that is ideally operated at the location of heat consumption but can also feed useful heat into a district heating grid. Here, we distinguish between the principle of power-heat cogeneration or heat-power cogeneration. Here, power and heat are generated and used as a priority, depending on requirements.

Self-ignition combustion engines (diesel engines) and gas engines but also gas turbines or Stirling engines can be used to drive the energy generators. It is also possible to use gas as a fuel in modified diesel engines. (dual-fuel engine)

Combined heat and power plants can thus be powered by a variety of fuels.

The reason for the higher total utilization rate compared to a conventional combination of district heating and central power plant is that the excess heat from power generation is used at its place of origin and does not go to waste, polluting the environment. Depending on the size of the plant, the efficiency factor of power generation without using the excess heat is between 22 and 35 %. If the excess heat is used locally, a total efficiency factor of approx. 80 to more than 90 % can be attained. By comparison, condensing boilers attain efficiency factors of around 100 % but cannot generate electric current.

CHP modules have electrical outputs of between one kilowatt (kW) and a few megawatts (MW). Below 50 kW these are referred to as mini-combined heat and power plants (mini-CHPs), below 15 kW they are referred to as micro-CHPs. Mini and micro-CHPs are used in private homes and apartment buildings, in commercial premises and housing developments. Cogeneration is also used in thermal power stations. Although here it is a greater power range of several hundred MW with connection to remote heating networks.