## 3 Results and Discussions  
### Indoor Characterization  
Indoor analysis lasted 2 h, a time sufficient to reach a steady-state temperature regime. In Figure 4, the experimental setup is shown. Both tests were performed at a simulated solar radiation of 1000 W/m\({}^{2}\). Both trends are depicted in Figure 5, where the blue line indicates the references case test and the red  
Figure 4: Experimental indoor setup. Figure 3: Spectral content of the lamps. one the enhanced panel. After a ramping of about 3 min, necessary to the lamps to reach the nominal power, the simulated radiation was around 1000 W/m\({}^{2}\). The comparison of the temperatures between the reference case and the enhanced PV panel is shown in Figure 6. The front temperature of the pure panel is depicted with the red line, while the blue line indicates the front temperature of the graphene/fins/PCM PV system. After around ten minutes, where the temperatures followed the same trend, at around 45 \({}^{\circ}\)C, the reference panel became warmer. At the end of the two hours, the front thermocouples mounted on the reference panel measured a temperature of 65.4 \({}^{\circ}\)C, while on  
Figure 5: Trend of the simulated radiation for the reference case (blue line) and the enhanced panel (red line). Figure 6: Comparison between the front temperature of the reference case (red line) and the enhanced panel (blue line) over the two-hours test. the enhanced panel 58.6 \({}^{\circ}\)C. The time taken to reach a steady-state temperature condition was investigated to estimate the major conductivity obtained by adding the graphene and the aluminum fins into the PCM. The slope of the trend was calculated by the following Equation (1):  
\[\Delta(i)=\frac{Tm(i)-Tm(i-1)}{Tm(i)}\times 100 \tag{1}\]  
where \(i\) is the time step, set in a minute, and \(Tm\)(\(i\)) and \(Tm\)(\(i-1\)) are the average temperatures over a minute in the current time step and in the previous one, respectively. \(\Delta\) is the slope of the temperature trend. The trend is considered in a steady-state regime when the slope (\(\Delta\)) was in a range of convergence of \(\pm 1\%\). Results were post-processed through the function \"polyval\" and \"polyfit\" on the software MATLAB to eliminate the signal noise. The results are shown in Figure 7. The increased conductivity was proved, as the reference case reached the steady-state condition after 20 min while the enhanced panel after only 14 min. This allowed the panel to be colder and, accordingly, the electric yield increased. Globally, over the two hours test, the temperature of the enhanced panel was 6 \({}^{\circ}\)C colder than the reference case one. Hypothesizing a temperature coefficient of 0.5%/\({}^{\circ}\)C for the monocrystalline PV panel, an increase of 3% in the electric yield was obtained. In Table 2, all the results are summarized. The enhanced panel was monitored for more than three hours, to allow the melting process to be completed. In Figure 8, the end of the process was visible in a change of slope. This occurred around 35 \({}^{\circ}\)C, for the first thermocouple (orange line), then dipped into the PCM after 1:20 h from the beginning of the test. For the second one, this happened after 2:30 h (blue line). When the change of slope occurred for the light blue line (2:45 h), representing the thermocouple mounted on the plexiglass box, the melting process was completed. In Figure 8, the trend of all temperatures is shown. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **T Average** & **T Peak (\({}^{\circ}\)C)** & **Ramping Time** & **Average Solar** \\  & (\({}^{\circ}\)C) & **T Peak (Minutes)** & **Radiation (W/m\({}^{2}\))** \\ \hline Ref case & 60.01 & 65.4 & 20 & 977 \\ Enhanced panel & 54.48 & 58.6 & 14 & 992 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Indoor test results. Figure 7: Convergence to the steady state regime (the blue line indicates the enhanced panel and the red one the reference case). Figure 9 visually shows the sequence of the same melting process.