## 3 Methods
### Estimation of the PV Potential from Solar EVs on Donghae Expressway
#### 3.2.3 PV Potential Estimation Model and Parameter Setting  
The PVWatts model developed by the United States National Renewable Energy Laboratory was employed to estimate the potential of solar EVs. This model, which can easily estimate PV power potential from eight inputs, has been used in numerous studies; therefore, it is deemed reliable. The specific PV power potential of the PV Watts model can be expressed using Equation (3), and the solar cell temperature estimation can be expressed using Equation (4).  
\[\textit{Power Generation}\ (\mathrm{kWh})=\frac{I}{1000}A\frac{n_{p}}{100}\frac{n_{i }}{100}R_{da}\frac{100-(25-T_{cell})\gamma}{100}\frac{L}{100} \tag{3}\]  
\[T_{cell}=T_{air}+\frac{NOCT-20}{800}I \tag{4}\]  
\(I\) indicates the hourly global horizontal irradiance (GHI) values from the closest meteorological station to the driving location of the EV, where the GHI (\(\mathrm{W/m^{2}}\)). This reflects the difference in insolation due to location, as the area of interest is more than 120 km long. \(A\) is the area (\(\mathrm{m^{2}}\)) of the PV modules installed horizontally on the bonnet and roof of a solar EV. \(n_{p}\) denotes the efficiency of the PV module (%), \(n_{i}\) is the efficiency of the inverter (%), \(R_{da}\) is the DC-to-AC conversion efficiency (%), \(T_{cell}\) is the temperature of the PV module (\(\mathrm{\SIUnitSymbolCelsius}\)), \(\gamma\) is the temperature coefficient (\(\mathrm{\SIUnitSymbolCelsius}\)), and \(L\) is other losses (%). Here, \(T_{cell}\) (\(\mathrm{\SIUnitSymbolCelsius}\)), which represents the temperature of the PV module, can be derived from the outside air temperature (\(T_{air}\)) (\(\mathrm{\SIUnitSymbolCelsius}\)) and nominal operating cell temperature (\(NOCT\)).  
Except for the weather characteristics, module specifications, and design values of the solar EV, the remaining factors to assess the PV potential of the solar EV employ the values presented in Table 2. Other loss rates that can significantly affect the PV potential results were assumed to be conservative to account for different environments and changing conditions. In addition, this study assumed that the EVs travel at a constant speed of 60 km/h to estimate the PV power potential. This is in accordance with the minimum speed limit applied to some sections of the Donghae expressway, and the maximum speed limit is 100 km/h.  
\begin{table}
\begin{tabular}{c c c} \hline
**Items** & **Design** & **Value** \\ \hline Module type & & mono-Si \\ \hline Module capacity & \begin{tabular}{c} Designed originally \\ Considered in this study \\ \end{tabular} & \begin{tabular}{c} 1208 W \\ 1095 W \\ \end{tabular} \\ \hline Module area & \
\begin{tabular}{c} Designed originally \\ Considered in this study \\ \end{tabular} &
\begin{tabular}{c} 7.5 m\({}^{2}\) \\ 6.8 m\({}^{2}\) \\ \end{tabular} \\ \hline Module efficiency & & 24\% \\ \hline Electric efficiency & & 5.6 km/kWh \\ \hline \end{tabular}
\end{table}
Table 1: Specification of solar EV (Sion) used for PV potential calculation [42].  
\begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Value** \\ \hline Inverter efficiency & 96\% \\ DC to AC ratio & 1.1 \\ Temperature coefficient & \(-0.5\%/^{\circ}\)C \\ Other losses & 20\% \\ NOCT (nominal operating cell temperature) & \(50\,^{\circ}\)C \\ \hline \end{tabular}
\end{table}
Table 2: Parameter values of the PVWatts model used for the PV potential calculation.