The topology or architecture of a microgrid is a function of the mixture of generation assets, customer loads, storage, smart switches, and whatever other technologies are incorporated into the structure. The versatility of the microgrid means it can range widely in size, source of generation, source of electric, heat and cooling demands – the list goes on. The modularity of this platform is one of its most attractive features.

Given this diversity and versatility, it is virtually impossible to map out what any typical microgrid looks like in terms of electrical configurations and/or boiler plate layouts: none exist. As one smart grid software provider described the situation: “Microgrids are like Baskin Robbins, but there are a lot more than 31 flavors.” The diagram below from the Institute of Electrical and Electronics Engineers (IEEE) provides a generalized topology of three types of microgrids: (1) a utility microgrid located on substation feeders; (2) a multi-facility microgrid that might be deployed as an industrial/commercial complex; and (3) a single facility microgrid that might include both residential and commercial buildings. The truth of the matter is that none of these three theoretical microgrids are expected to dominant microgrid markets over the next five years, but this diagram is instructive in highlighting how microgrid structures differ from one another. There are no rules; there are only exceptions when it comes to microgrids.

The three leading end-use applications that are under current deployment today are the following; each tends to have a different topology, especially remote systems:

Institutional/Campus Microgrids: The typical focus of these microgrids is to aggregate existing on-site generation with multiple loads that are co-located in a campus setting. These microgrids tend to be among the largest and therefore may require master controller systems. Along with boosting reliability, the microgrid may be viewed as a way to increase revenue streams from on-site power generation (and storage) by selling these energy services to the utility hosting the local distribution grid. The University of California-San Diego microgrid is probably the best example of this segment. The 45 MW facility is scheduled to come on-line before the end of 2010. Leading control technology providers include EDSA Power Analytics and Viridity Energy.

Military Base Microgrids: The focus of these microgrids is security, both cyber and physical. Since the Department of Defense (DOD) has a mandate to shift over to renewable energy supplies as a matter of national security, distributed renewables will have to play a vital role. Many of the DOD projects fall under the category of “energy surety microgrids,” a concept developed by Sandia Labs, highlighting the priority given to maintaining secure supplies to mission critical functions of a military base. These microgrids are really a series of concentric smaller and smaller redundant microgrids. The Fort Sill, Oklahoma microgrid – still under development – is a good model here. The facility is expected to total approximately 5 MW. Encorp is a leader technology controls provider.

Remote “Off-grid” Microgrids: Since these microgrids never connect to a larger grid, and therefore operate in an island mode on a 24/7 basis, there is a greater need for storage than other topologies. Many of these microgrids are designed to reduce diesel fuel consumption by integration of solar PV, distributed wind or, as is the case with the Bella Coola project in British Columbia, run-of-the-river hydropower. General Electric is working with B.C. Hydro on the Bella Coola project, and has identified 300 other sites in Canada alone that could serve as host sites for microgrids that generally are about 100 kW in size.

Architecture of microgrids is about technological design, while end-use application segments are linked to purpose. Each of the three segments expected to dominant the microgrid market until 2016 feature a single owner. Microgrids with multiple owners are rare – except in Japan.

Barriers to implementation of mixed owner commercial/industrial or community/utility segments are not based so much on the topologies themselves, but rather on the commercial aspects of managing transactions. What happens if multiple owners have competing agendas? Solutions to this dilemma may have to echo what has been done at the transmission level with an Independent System Operator, a financial settlement system divvying up costs and financial obligations among the different microgrid owners. At present, not a single country in the world has such a system in place, though Denmark is the furthest along in designing such policy instruments.