## 3 Results and Discussion
### Extraction of Solar Module Parameters from the Measured Dark I-V Curves  
Once the dark I-V curves onsite measurements have been presented, the main parameters of the one exponential model (single-diode model) of each module are obtained using the 2/3 Diode Fit software. These results are presented in Table 3. In order to have comparative results between the different modules, parameters are presented in relation to the area. With the objective of drawing some conclusions on the state of the analyzed PV modules and for comparison purposes, all dark I-V curves have been presented in the same graph in Figure 8 and are analyzed together with their main parameters in this subsection. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Module Number** & **Ambient Temperature** [\({}^{\circ}\)C] & **Cell Temperature** [\({}^{\circ}\)C] \\ \hline
1 & 14.5 & 14.7 \\
2 & 14.4 & 14.7 \\
3 & 14.4 & 14.5 \\
4 & 14.4 & 14.7 \\
5 & 14.6 & 15.4 \\
6 & 15.3 & 16.2 \\
7 & 14.6 & 16.7 \\
8 & 14.8 & 16.1 \\
8 & 14.7 & 17.0 \\
9 & 14.8 & 16.5 \\
10 & 15.0 & 16.9 \\
11 & 15.0 & 21.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Ambient and cell temperatures of each module at the I-V curve measurement. Figure 8: Dark I-V curves of the eleven modules measured with the developed device at the PV installation in Campus Duques de Soria. First, it can be observed from Figure 8 is that there is one curve--number 10 from module 10--that has different characteristics from the rest. This is reflected in the extremely high value of the saturation current that, combined with the high value of the diode factor, dominates the rest of the model parameters. For the curves that belong to the same module type (1, 2, 3, 4, 5, 7, 8, and 9), some differences can also be appreciated. If we fix a current equivalent to \(I_{sc}\), we find that different voltages are found for the I-V characteristics. Given that all the curves are measured at approximately the same temperature, these variations would indicate different degradation in these modules. Furthermore, changes in the slope in the high-voltage area indicate changes in series resistance (higher slope, lower series resistance). It has to be taken into account that these modules have a lot of damages, some of them appreciated by the naked eye (see the upper row of modules in Figure 6), and various degradation modes are mixed, influencing the measured dark I-V curves. Higher series resistance modules indicate degradation in the module electrical circuit (modules 1, 3, and 7). High series resistance, combined with lower shunt resistance and diode saturation current could inform about mechanical damage [31] (for example, module 3). It is also observed that some modules, especially those numbered 7, 8, and 2 present a very low value of shunt resistance (see Table 3). This low value of shunt resistance is also found in the other EOPLLY module (165W type), and in the number 10 module, which presents high degradation in all parameters. These low values of shunt resistance would imply shunting loses in the module. The combination of a lower \(R_{sh}\) and higher \(J_{0}\) in modules 2 and 8 would indicate that the recombination losses are also enhanced in these modules. With reference to the I-V curves presented, other interesting ideas can be pointed out. Differences between curves (in the 35-50 V range) are a consequence of the combination of parameters that can have opposite effects (for example, \(J_{0}\) and \(n\)), so it is very difficult to grasp differences among the degradation states of several modules by solely comparing their I-V curves in a certain moment (except for cases as that of module 10), one to each other. In this case, the rightmost curve corresponds to module 1 (\(J_{0}\) = 7.87 \(\times\) 10\({}^{-9}\) A/cm\({}^{2}\) and \(n\) = 1.73), while the leftmost is of module 7 (\(J_{0}\) = 3.98 \(\times\) 10\({}^{-12}\) A/cm\({}^{2}\) and \(n\) = 1.04).