# Highway Microgrid Project Evaluation under Energy Transportation Integration
## 2 Highway Microgrid Evaluation System
### Index Evaluation Comotation  
#### 2.2.1 Economic Index  
The investment cost and maintenance cost should be considered in the highway microgrid project. The investment cost is the purchase and placement cost of the equipment of each unit of the system, and its calculation formula is as follows [24]:  
\[C_{\text{A}}=\sum_{i=1}^{4}\frac{P_{i}c_{i}r(1+r)^{N}}{(1+r)^{N}-1} \tag{1}\]  
where \(i=1,2,3,\) and \(4\) correspond to the wind turbines, photovoltaic arrays, energy storage devices, and charging piles; \(P_{i}\) is the rated installed capacity; \(r\) is the discount rate; \(N\) is the planning cycle; \(c_{i}\) is the annual unit investment cost. The operation and maintenance cost of the highway microgrid project involves the costs generated by the routine maintenance of new energy power generation devices, the cleaning of photovoltaic panels, the maintenance of slopes along the highway, and the penalty costs generated by noise [25; 26]. 1. Routine maintenance cost  
After the highway microgrid project is completed and placed in service, it needs to maintain the equipment, which costs routine maintenance. The routine maintenance cost per unit capacity of each piece of equipment determines its annual routine maintenance cost. \[C_{\text{RM}}=\sum_{i=1}^{4}P_{i}c_{i}^{\prime} \tag{2}\]  
where \(c_{i}^{\prime}\) is the annual unit maintenance cost of wind turbines, photovoltaic arrays, energy storage devices, and charging piles. 2. Slope maintenance cost  
The purpose of highway slope maintenance is to prevent landslides, collapse, and other dangerous situations on the slope, and ensure the normal operation of highway photovoltaics. \[C_{\text{SM}}=\frac{nh}{\cos\alpha}c_{\text{SM}} \tag{3}\]  
where \(n\) is the slope number; \(h\) is single-stage slope height; \(\alpha\) is the slope angle; \(c_{\text{SM}}\) is maintenance cost per unit area. 3. Dust removal maintenance cost  
Small particles in the air easily accumulate on the photovoltaic panel to form ash, which reduces the power generation performance, so it is necessary to clean the ash regularly. Dust removal maintenance costs due to ash accumulation and cleaning include power loss cost and cleaning cost. \[C_{\text{DRM}}=(C_{\text{d}}+C_{\text{c}})\cdot\beta \tag{4}\] \begin{table}
\begin{tabular}{c c c} \hline \hline
**Overall Index** & **Primary Index** & **Secondary Index** \\ \hline \multirow{6}{*}{comprehensive index evaluation system} & Economic index & Net Present Value \\ \cline{2-3}  & & Internal Rate of Return \\ \cline{2-3}  & & Internal Rate of Return \\ \cline{2-3}  & & Energy use efficiency \\ \cline{2-3}  & & Power supply reliability \\ \cline{2-3}  & Environmental benefit index & Carbon emission reduction \\ \cline{2-3}  & & Emission reduction benefit \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Index evaluation hierarchy structure. where \(C_{d}\) is the power loss cost generated during a single cleaning interval; \(C_{c}\) is the cleaning maintenance cost generated by a single cleaning; \(\beta\) is the cleaning frequency. 4. Noise penalty cost The operation noise of the equipment is unavoidable. If the noise pollution generated exceeds the national standards for environmental noise, a noise penalty cost shall be paid.