Structures of small power supply networks and a practical example with renewable energy resources

Dispersed generators have been expected to be effective measures to tackle issues such as energy cost reduction, environmental preservation, and/or energy security. This, coupled with the evolution of deregulation, has set a stage for new types of business in electric power industry. With these backgrounds, small power supply networks, such as microgrids, are attracting much attention in recent years, as being a new technology to coordinate dispersed generators with utility grids. The present paper describes the status of small power supply networks in Japan. First, the transition of regulation in Japan will be outlined. Following this, results from a field test of a small supply network, which is called ldquoRegional Power Gridrdquo, will be discussed. Emphasis is placed on the energy management system, which organizes controllable and uncontrollable dispersed generators into a single controlled unit while minimizing operational costs and environmental impacts. The system has been in operation since October 2005, and shown to be a promising way to facilitate greater introduction of dispersed generators, especially photovoltaic and wind power generation systems.