3.4 DER Capabilities and DER System Architectures

3.4.5 Microgrids and “Nanogrids”

A microgrid is defined as small grids that may be connected to the utility grid but can also disconnect from that grid and continue to operate.  Nanogrids are just very small microgrids and could range from an office building down to residential homes or even smaller.
Some microgrid characteristics include:

• Geographically delimited
• Connected to the main grid at a single Point of Common Coupling (PCC)
• Capable of operating either connected to the utility or in islanded mode
• Includes DER systems as the source of power, which may be combinations of renewable, fossil fuel-based, inverter-based, synchronous, energy storage, and controllable load
• Includes an energy management system that manages (among other activities) the disconnection from the main grid, the islanded operation, and the reconnection back to the main grid

A microgrid can provide several different services to the utility grid. From the system operator’s perspective, a microgrid can either serve as:

• A flexible energy resource that can be bid into the electric market;
• A fast-responding remedial action scheme implementation that can have varying impact to the customer (i.e. on-demand islanding);
• An ancillary service resource, or;
• A “ramp down” variable consumption resource (in response to over generation conditions)

Technical requirements are still being developed on the transitions from connected to disconnected and back to reconnected.  Additionally, the financial issues around deploying and utilizing microgrids for grid support are still under wide-ranging discussions. A standard, IEEE 2030.7, is being developed on these topics.