How do I size my cogeneration system?

A cogeneration unit produces electricity at an efficiency generally in the range of 20% to 45%, depending on the technology used. The input energy that is not converted to electricity is converted to heat, a large portion of which may be harnessed for such uses as hot water or space heating.

Typically in a commercial situation, a cogeneration unit should be sized and operated to match the actual heat requirement – so it is likely to run for longer periods in colder weather and shorter periods in hot weather. If it is oversized to produce more electricity, there may be excess heat which will be dumped because there is nowhere for it to be used.

A cooling system that can use heat (e.g. an absorption or desiccant cooling system) can be installed to increase the hours of operation in summer, when it is often more profitable to generate electricity.

It may be cheaper and simpler to size a cogeneration unit so that all of its electricity output is used within the development: negotiating contracts to sell power to an electricity retailer can add to complexity and costs.