# Understanding Microgrid Sustainability: A Systemic and Comprehensive Review
## 3 Energy Field
### Energy Issues  
Based on the literature, this work considers the energy field to have three main issues: appropriate system sizing, quality of the components, and protection [121; 122; 123; 124]. Appropriate system sizing refers to the correct balance of the different electrical elements [32] and the conformity of the microgrid to the needs [33] and earnings of its final users [34]. The microgrid sizing must balance being large enough to avoid any outages and small enough to remain as affordable as possible for final users [125; 126]. This sizing problem can be broken down into a multitude of critical factors ranging from the optimization of the sizing of storage systems [127] to the understanding of local energy needs [128] or the balance of different energy sources [129], but also by addressing more specific issues such as the optimization of the integration of hydrogen fuel cells [130]. The quality of components describes the microgrid equipment in terms of robustness and maintainability [35]. The current literature points out that higher quality of the electrical grid components as a whole avoids blackouts and dysfunctions [36], which is a crucial element, especially in rural areas [37]. For this, important knowledge of the technologies available for the implementation of microgrids is required [96; 100; 131]. However, it is essential to keep in mind that these systems change and evolve rapidly, and the quality of the grid also requires regular upgrades and maintenance [97; 123] which have been summarized in terms of robustness, resourcefulness against disasters, rapid recovery, and adaptability [132]. Protection of the microgrid refers to the equipment and techniques used to protect the elements of the energy system from any malfunction, whether internal or external to the element [38]. An extensive review has been conducted to present all the protection possibilities in AC [39] and DC [40] grids and different standards [41]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Architecture** & **Type** & **Advantages and Drawbacks** & **Articles** \\ \hline \multirow{3}{*}{**AC**} & \multirow{3}{*}{AC microgrid} & AC microgrid is really easy to implement and reconfigure but requires a complex power electronic interface and a generally poor quality energy & [40; 110] \\ \cline{3-4}  & & DC microgrids are relatively simple to control with a relatively good quality of energy but tend to be limited in terms of expansion and their lack of reliability with a distribution grid connection & [39; 111] \\ \hline \multirow{6}{*}{**Hybrid**} & \multirow{3}{*}{AC-DC microgrid} & Combines the advantages of AC and DC architecture but cannot be suited for all applications & [112] \\  & & & More reliable storage devices and has similar performance to the hybrid & \\ \cline{1-1} \cline{3-4}  & & AC-DC, but the energy storage must be centralized & \\ \cline{1-1} \cline{3-4}  & & & Allows different buses voltage and management technique but increases & \\ \cline{1-1} \cline{3-4}  & & the complexity of the control & \\ \cline{1-1} \cline{3-4}  & & Solid state transformer based microgrid & Very high quality of energy and high compatibility with AC or DC devices, & \\ \cline{1-1} \cline{3-4}  & & but the entire grid is dependent on the solid state transformer & \\ \cline{1-1} \cline{3-4}  & & & Easy development and high overall reliability and flexibility, but requires a complex power electronic interface & [119] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Classification of microgrid power architecture. In the energy field, sustainability translates as defining clear thresholds for the issues of sizing, quality, and protection. Sizing should provide a compromise between power production capacity and foreseeable load. Quality is the cost-benefit analysis of the equipment used to build the microgrid. Protection is the number of protection elements for different faults and the overall cost linked to their presence or absence from the microgrid.