# Investigation of Nanogrids for Improved Navy Installation Energy Resilience
## 2 Background and Related Research
### Energy Resilience  
The focus of this paper is on improving energy resilience of military bases, and specifically for critical loads, through the implementation of nanogrids. In order to understand the amount of improvement in resilience a proposed nanogrid may have over existing microgrid infrastructure, a working definition of resilience in this context and a quantitative means of measuring resilience must be defined. Rather than adopting a civilian-focused energy resilience definition and quantification, it is important to first understand the value of and difference in resilience from a military perspective. Civilian grid systems often focus on defining resilience in terms of real dollars lost when energy supply does not meet demand and a facility stops production of something that is easily monetized (e.g., steel, automobiles, computer chips, processed food, vaccines, etc.) [21]. Conversely, military energy systems such as nanogrids and microgrids produce something less tangible: national security [22]. National security is intangible and has no easily defined value [22,23]. The cost to national security due to lack of energy resilience becomes subjective and theoretical [24]. There are a variety of definitions of energy resilience within military communities although they all focus on several commonalities: preparing for an event, riding out the event, stabilizing after the event, and recovering from the event in order to continue to support mission essential operations and maintain readiness [5,25]. The military definitions of energy resilience generally align with civilian definitions although the military definitions always tie back to the mission of national security [5,26]. Thus, this paper adopts thedefinition of energy resilience from a military perspective as encompassing the ability of an energy system to support critical loads before an event, during an event, immediately after an event, and in the recovery from an event back to a normal operating state. There have been several attempts to quantify energy resilience for military purposes from a financial perspective. For instance, a cost benefit analysis of stand-alone diesel generators attached to critical loads on installations was performed to calculate a Customer Damage Function (CDF) which is representative of the cost of interruption as a function of the duration of an outage [21; 27]. However, in most situations it is very difficult to quantify national security in a dollar amount. Instead, within the United States military, the value of resilience is sometimes defined using the Mission Dependency Index (MDI) where MDI captures the relative criticality of various infrastructure on a base with respect to the mission of the tenant organizations on a base on a 0-100 scale with 100 being absolutely critical [28]. In contrast, some researchers have criticized the use of MDI when directly ranking criticality of loads to their overall role in national security missions. These researchers claim existence of inaccuracies in addressing time dependency of corrective actions, and misrepresentation of mission interdependence and intradependence in the MDI equation [29]. Recently the DoN has begun using Resilient Energy Program Office (REPO) (an attempt to address the shortcomings of MDI with similar objectives and using aspects of Energy Security Assessment Tool (ESAT)) as a replacement in some of the roles that MDI has been previously employed [30]. However, many organizations across the United States federal government retain MDI and some issues with REPO are currently being identified. Thus, this paper adopts MDI as the base measure of a unit of energy resilience. In order to use MDI to quantify energy resilience for the military, a method of quantifying resilience over time is needed. Several exist or are in development [5; 22; 26; 31; 32]. This paper adopts the approach proposed by [PERSON] et al.