Shape of the microgrid

Restrictions on expansion of traditional centralized generating and delivery systems may be becoming so tight in the industrialized countries that they cannot reasonably be expected meet future electricity demand growth at acceptable cost. Meanwhile, technological advances, notably improved power electronics that permit grid interconnection of asynchronous generation sources, is tilting the economics of power generation back towards smaller scales, thereby reversing a century long trend towards the central control paradigm. Special power quality requirements or opportunities for combined heat and power applications make on-site generation an even more attractive option for customers. The existence of a significant amount of electricity sources dispersed throughout the low voltage distribution system could create a power system quite different to the one we are familiar with and creating it offers significant research and engineering challenges. Moreover, the electrical and economic relationships between customers and the distribution utility and among customers may take forms quite distinct from those we know today. For example, rather than devices being individually interconnected in parallel with the grid, they may be grouped with loads in a semi-autonomous neighborhood that could be termed a microgrid. A microgrid is a cluster of small (by the standards of current power systems, e.g. < 500 kW) sources, storage systems, and loads which presents itself to the grid as a legitimate single entity. The heart of the microgrid concept is the notion of a flexible, yet controllable electronic interface between the microgrid and the familiar wider power system, or macrogrid. This interface essentially isolates the two sides electrically; and yet connects them economically by allowing delivery and receipt of electrical energy and ancillary services (EE&AS) at the interface. From the customer side of the interface, the microgrid should appear as an autonomous power system meeting the power quality and reliability requirements of the customer. Such issues as local voltage, reliability, losses and quality of power should be those that support the customers' objectives. From the macrogrid side, however, the microgrid should appear as a legitimate entity akin to current interconnected generators or loads. A key distinction between microgrids and our familiar arrangements is the expanded role of electricity endusers in determining the pattern of development of the overall power system, which must not only accommodate purchases and sales of EE&AS to and from established markets but also contractual agreements between microgrids. Fundamentally, the characteristics and capabilities of the microgrid will be determined by its internal requirements together with the technical, economic, and regulatory opportunities and constraints it faces, and not by established objectives for capacity expansion and reliability of the macrogrid. The goal of Consortium for Electric Reliability Technology Solutions (CERTS) work underway at the Berkeley Lab is to anticipate possible patterns of microgrid development that can help focus research efforts on the key technical problems that must be solved to enable microgrid deployment