In order to build a holonic energy supply system within the urban area in the next 21 century, the electricity generated by the nuclear power plants or by the coal fired power plants is used for the base load demand, and the electricity generated by small-sized cogeneration plants distributed within urban area is used for the peak load demand. Such cogeneration plants should burn imported oil and LNG, and should supply heat simultaneously. The big concentrated system as nuclear plants and the small distributed systems as cogeneration make up weakness each other. In the next century, people want the amenities of life so that they need the varieties for the energy supply. For example, people may demand variable voltage or variable frequency for the electricity, even direct current.
In such era, the cogeneration systems seem to have strong capability. This paper discusses the trend of technological developments of cogeneration and the points to be politically brushed up.