# Investigation of Nanogrids for Improved Navy Installation Energy Resilience
## 2 Background and Related Research
### Military Microgrids  
Many military bases and other critical facilities have or are in the process of implementing microgrids, at least in part in an attempt to provide reliable energy to critical loads. Microgrids on many military bases generally perform six key functions for the attached critical loads including: (1) stepping down high voltage power received from the main utility grid to intermediate and/or low voltage, (2) distribute energy to critical and non-critical loads, and connect other electrical hardware, (3) generate energy locally (e.g., diesel gensets, Photovoltaic (PV) arrays, wind turbines, etc.), (4) store energy (e.g., battery banks, pump-storage hydro, etc.), (5) control the flow of energy, the generation, the storage, and the loads throughout the microgrid using one or more controllers to automatically operate electrical equipment, (6) step up and down voltage (transformers) and convert energy from AC to DC or vice versa (inverters and converters) [12,13]. The main components of a microgrid often include diesel generators and other fossil fuel generators; PV, wind turbines, and other renewable energy sources; energy storage systems such as battery banks; Points of Common Coupling (PCC) where the microgrid connects to the utility grid (generally with a switch to allow for operation of the microgrid while disconnected from the utility); one or more control systems (often involving Supervisory Control and Data Acquisition (SCADA) systems); and switches, converters, inverters, relays, transformers, power lines (above ground, underground, etc.), and other related hardware.  
An established PCC and other requisite hardware (grid-forming generation and/or storage, generation, local controller(s), etc.) provides one of the primary benefits of microgrids for military bases and other critical facilities. The PCC provides the ability to disconnect from the main utility grid, called \"island-mode\" [14], and continue uninterrupted service of critical loads. In island-mode, loads critical to a military base's primary mission functions (the critical loads) are still provided power from local generation and storage sources [14]. Issuances and instructions from organizations within militaries such as the NAVFAC generally state that in order for military bases to perform their missions, energy security of critical loads must be ensured regardless of the state of the grid beyond the PCC and outside of the microgrid system boundary [8]. One way of identifying critical loads in the United States military is the Mission Assurance and Continuity of Operations plan for DOD installations which instructs that the essential buildings needed to conduct national security missions based on criteria identified by the individual branches of the military (e.g, DoN, etc.) and the installation mission must continue to receive power even during utility disruptions (e.g., external power to a base is cut) [8].  
Military microgrids have found several benefits in use including integrating smart grid technologies, reducing peak load and losses by enhancing integration of Distributed Energy Resources (DERs) (often including diesel gensets, wind turbines, micro hydro generation, fuel cells, PV, and other generation sources), localizing power quality and reliability for end-user satisfaction, and supporting the utility grid by managing sensitive loads and variability of DERs [10,15]. Currently military microgrids are allowing the interconnection of loads and DER that can replace duplicitive and expensive-to-maintain small Uninterrupted Power Supply (UPS) and stand-alone backup generators [10]. The flexible architecture of microgrids eases the employment of DER in conjunction with controllable loads and storage devices [15,16].