## 3 Results and Discussion  
### Modules Comparison  
For each module, more than 35 sets of _I-V_ curves were obtained in an equal number of operation points and as close to each other as possible. Figure 5 shows the in-plane global irradiance, ambient temperature, and time instants required for tracing each set of curves for the three modules. As is observed, the _I-V_ curves were obtained in at least one case of  
Figure 4: Mounting of bPV1 and bPV2. Experimental setup (**a**) and obstruction scheme (**b**).  
Figure 3: Single-face bPV characterization setup.  
the main sky conditions: three clear-sky days (14-16 February), one with passing clouds (17 February), and a final overcast one (20 February).  
A summary of the outdoor results can be seen in Figure 6, where the maximum power (a), short-circuit current (b), open-circuit voltage (c), and modules temperature boxplot (d) can be observed. The superior generation performance of bPV over both PV1 and PV2 is evident (Figure 6a). At three different irradiance levels of 300, 600, and 900 W/m\({}^{2}\), and considering the linear regressions shown on Figure 6a, bPV would proportionally produce up to 6.4% more than PV1 and 7.8% more than PV2 (the remaining values are shown in Table 3).  
Similar behaviors can be observed when analyzing the SC current (\(I_{sc}\)) (Figure 6b). The bifacial module's current capacity is always higher than the two conventional modules (PV1 presents slightly better characteristics than PV2). Once again, linear fitting allows the quantification of the additional current, the current increments are given at 900 W/m\({}^{2}\): 3.78-5.37% (for PV1 and PV2, respectively).  
As expected, no particular OC voltage (\(V_{oc}\)) improvement is observed, as bifacial devices modify power through the increase in the total photogenerated current, and this has a logarithmic relationship with \(V_{oc}\). Indeed, bPV demonstrates an intermediate behavior between PV1 and PV2 (Figure 6c).  
The temperature operation is a critical performance feature as its increment reduces PV efficiency and accelerates cell degradation [38]. It has been suggested that bifacial modules would operate at lower temperatures than conventional PV ones [39; 40], with an estimated reduction of around 1.1 \({}^{\circ}\)C [40]. Our experimental results show that it could be the case  
Figure 5: In-plane irradiance (30\({}^{\circ}\)), ambient temperature, and instant of \(I\)-\(V\) samples for modules PV1 (green-x), PV2 (red-+), and bPV (blue-o). 18–19 February were not labor days, and no \(I\)-\(V\) curves were obtained.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Front Irradiance**} \\  & & **300 W/m\({}^{2}\)** & **600 W/m\({}^{2}\)** & **900 W/m\({}^{2}\)** \\ \hline \multirow{3}{*}{\(\frac{P_{up}}{P_{up},ST}\) [\%]} & PV1 & 27.5 & 53.4 & 79.3 \\  & PV2 & 26.8 & 52.3 & 77.9 \\ \cline{1-1}  & bPV & 31.8 & 58.8 & 85.7 \\ \cline{1-1} \cline{2-5}  & bPV-PV1 & 4.3 & 5.4 & 6.4 \\ \cline{1-1}  & bPV-PV2 & 5.0 & 6.4 & 7.8 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Potential power increment according to linear regressions at different front irradiance levels.  
but not necessarily (see Figure 6c and Table 4). If bPV and PV1 are compared, a lower temperature is consistently observed in bPV (mean, median, and lowest boxplot values, excluding outliers). However, no significant difference is observed in the same metrics when compared to PV2. More experimental results are required to fully understand these discrepancies. However, from this point of view, it seems that the bifacial modules would operate under temperatures, at most, as conventional PV devices.