What is a microgrid?

The topic of “microgrids” has come up in Hawaii in numerous forums of late.  Several parties in the Hawaiian Electric Company’s Power Supply Improvement Plan proceeding at the Hawaii Public Utilities Commission (Docket 2014-0183) have raised the issue of microgrids.  In the 2017 Hawaii Legislature there are no less than 4 House Bills (and several companion Senate Bills) that pertain to microgrids (HB848, HB1163, HB1248, and HB1280).  

Microgrids can be beneficial, but only under certain circumstances.  Few, if any of the microgrid proponents and none of the proposed legislative Bills have detailed a value proposition for microgrids, or what it will take for microgrid opportunities to be realized.  This series of blog posts will provide energy end-users, policy makers and other stakeholders with a basic foundation for understanding the topic of microgrids.   Today's topic:  What is a Microgrid?  

The U.S.. Department of Energy Microgrid Exchange Group defines a microgrid as “ … a group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid. A microgrid can connect and disconnect from the grid to enable it to operate in both grid-connected or island-mode.”  

The CIGRÉ C6.22 Working Group Microgrid Evolution Roadmap defines microgrids as “… electricity distribution systems containing loads and distributed energy resources, (such as distributed generators, storage devices, or controllable loads) that can be operated in a controlled, coordinated way either while connected to the main power network or while islanded.”

In other words, a microgrid can be thought of as an electric power system where generation and load are balanced in real time, just like in a larger power system, but the microgrid is typically contained within a subset (e.g. a single customer’s premises) of the larger utility’s loads and resources.  An interconnected microgrid is, at any given time, a load or a resource in relation to the larger utility grid, that is, it imports power or it exports power.  A microgrid that operates autonomously from the power grid (either temporarily or permanently), also referred to as “islanding,” must function reliably on its own with no support from the larger grid.  If the islanding is temporary, it must also be designed to re-connect to the larger power grid without causing a disruption in either the utility grid or the microgrid itself.  

AUTHOR'S NOTE:  It is important to note that the definitions discussed here are technical definitions, rather than legal or policy definitions.  A future post will discuss policy issues around microgrids.

Our next topic in this series is:  What are the Value Propositions for Microgrids?  

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