When thinking about Combined Heat & Power (CHP), the first consideration should be whether the building requires the simultaneous need for electricity and heat over extended operating periods, typically more than 6,000 hours a year, or 17 hours a day. The longer the operating hours the greater the economic and environmental benefit delivered by CHP to the end user.

Thermally, the CHP unit should be selected to match the base heating load of the site to maximise the running hours. For internal combustion engine based technologies the key to success of a CHP scheme is integration with the building’s heating system. The CHP unit must be installed as lead heating appliance with existing or new boiler plant providing additional capacity to satisfy peak demand.

From an electricity generating perspective, the CHP unit should be selected to meet the site’s base load. This avoids or minimises the “spilling” or exporting of electricity to the grid network, which on many sites would not offer a financially viable proposition. The key to maximising the economic benefit of the CHP scheme is to utilise all the electricity generated on site. When operating in parallel with the local supply network, any electricity required above the output of the CHP unit would be imported from the grid network. 
 
Retro Fitting or New Buildings

For new homes, it is cheaper and more efficient to specify better insulation than a micro CHP unit. However, if a space heating demand still exists and there is a substantial demand for domestic hot water, it may then be appropriate to install micro CHP. Retro-fitting a CHP unit is a relatively simple procedure similar to replacing a conventional hotwater boiler.