A combined heat and power (CHP) unit simultaneously produces both heat and electricity from the same fuel. Recovering the heat by-product reduces the losses associated with electricity production.

A CHP unit is comprises 4 main parts:
- Engine - to drive the generator
- Generator - to produce electricity, which is fed into the building's power distribution system
- Heat recovery system - to recover usable heat from the engine
- Control system - to maintain safe and efficient operation

The whole unit is enclosed in a special casing that reduces the noise and protects the components.

The engine can be powered by gas, diesel or plant oil (engines will have to be adapted for this last option). Much heat is generated as a result of the combustion of the fuel and the associated movement of the generator. This heat, lost from the generator casing or the exhaust, can be recovered using a heat exchanger.

Cogeneration of heat and power greatly increases the efficiency of each unit of fuel. In traditional electricity generation, the efficiency of generation is just 35%; that is for energy 100 units of fuel input, only 35 units are converted into useful energy and 65 units are rejected as waste heat! With a CHP system, this 'waste heat' is converted into around 45 units of useful heat. CHP units can be from 80-90% efficient.

CHP units can be incorporated into community heating systems. CHP is a suitable technology for most developments with a high heat load, such as care homes, hospitals, hotels etc..

The CHP unit must be sized to the predicted heat requirements, usually of the summer months. The winter heat load will generally be a lot greater, which would result in a system operating inefficiently, under part load during the summer,

In some cases the noise of the system may be disruptive, even in its sound-reducing enclosure. The system will require regular maintenance although this can generally be arranged with the installer.

Economies of scale are to be had with CHP installations. A 5.5kWe/12.5kWh unit would cost around £12000 fully installed (about £1000/kWh) and a 12kWe/30kWh unit about £21000 (about £700/kWh).

Please email or call CEN on 020 8683 6694 for further information or advice.