Energy saving potential of cogeneration system in commercial and residential sectors in Japan

This paper proposes a new approach to evaluate a cogeneration system (CGS). From the viewpoint of total efficiency of the whole energy system, we evaluated the minimum efficiency required for a CGS to be introduced in the commercial and residential sectors in Japan. As a result, it has been revealed that the minimum efficiency required for the introduction of a CGS would be higher than that evaluated from the conventional viewpoint such as efficiency in the individual demand. This is attributed to the following. In order to make efficient use of a CGS, it should be operated to meet the changing heat demand without waste heat output, resulting in a low annual load factor of CGS. On the other hand, a new-type generator with high efficiency can be operated with a high annual load factor throughout the year. When the efficiency of CGS is not high enough, it is preferable for the whole energy system to replace the output of old-fashioned low-efficiency generators with advanced new ones rather than with a CGS.