“Microgrids are localized grids that can disconnect from the traditional grid to operate autonomously. …Microgrids support a flexible and efficient electric grid by enabling the integration of growing deployments of distributed energy resources such as renewables like solar.” (US Dept of Energy)

A more technical definition comes from the Lawrence Berkeley National Laboratory (Berkeley Lab):

A microgrid is a localized group of electricity sources and sinks (loads) that typically operates connected to and synchronous with the traditional centralized grid (macrogrid), but can disconnect and maintain operation autonomously as physical and/or economic conditions dictate.

There is also no specific guidance on the size of microgrids. Instead, microgrid definitions focus primarily on two features:

  • A microgrid is a locally controlled system
  • A microgrid can function both connected to the traditional grid (megagrid) or as an electrical island.

There are two major types of microgrids, as discussed in building-microgrid.lbl.gov/types-microgrids. These include microgrids wholly on one site, akin to a traditional utility customer, which are usually called customer microgridsor true microgrids (µgrids), and microgrids that involve a segment of the legacy regulated grid, often called milligrids (mgrids).