## 3 Results of Field Tests
### The Second Stage Experiments
Figure 10b  
Figure 9: Image of second stage experiment 1.1 that the solar module has cell defective. (**a**) IR origin image. (**b**) Gaussian filtered grayscale image. (**c**) Gaussian filtered color image. (**d**) Histogram of thermal temperature image. (**e**) Cumulative chart of thermal temperature image. (**f**) Cumulative chart-comparison of normal operation and abnormal conditions of solar modules. shows an image converted to grayscale after Gaussian filtering that the bright area still appears clearly after filtering. Figure 10c shows a 3-D color image of the temperature distribution with a high rise hill occurs at the hot spot at about 55 \({}^{\circ}\)C. Panel frames are at the temperature of 40 \({}^{\circ}\)C while the rest of the panel is at around 43-48 \({}^{\circ}\)C. Figure 10d shows a histogram of the temperature distribution. The PDF curve still looks like a beta distribution function and the bump with 40 \({}^{\circ}\)C corresponds to panel frames. The mean temperature is 44 \({}^{\circ}\)C with the deviation of \(-11\)\({}^{\circ}\)C. The maximum temperature is 55 \({}^{\circ}\)C and the minimum temperature is 30 \({}^{\circ}\)C. Figure 10e displays the cumulative temperature distribution that the percentage of hot spot area over 50 \({}^{\circ}\)C is 2.8%, indicating there are two cells exceeding the temperature threshold. Finally, Figures 5e and 10e are superimposed in Figure 10f for comparing normal and abnormal conditions. Figure 10e shows that the area over 50 \({}^{\circ}\)C is about 2.8%, which is higher than the 1.5% threshold presumed for a normal solar module, indicating that almost one cell has abnormality or failure. The above description shows that 97.2% of the panel is within the normal area, as shown in Figure 10d,e. This is consistent with Figure 10a-c, showing that bright area of hot spot is clearly visible. The original IR image of the third panel at the same location is shown in Figure 11a with a clear and bright area in the bottom left that corresponds to defected cells while a less bright area located in the upper middle is the junction box as mentioned before. Figure 11b shows an image converted to grayscale after Gaussian filtering. The grid  
Figure 10: Image of second stage experiment 1.2 that the solar module has one cell defective. (**a**) IR origin image. (**b**) Gaussian filtered grayscale image. (**c**) Gaussian filtered 3-D color image. (**d**) Histogram of thermal temperature image. (**e**) Cumulative chart of thermal temperature image. (**f**) Cumulative chart-comparison of normal operation and abnormal conditions of solar modules. in this image is still clearly visible after Gaussian filtering because the resolution of the original picture is higher for the third panel and the bright region still appears clearly after filtering. Figure 11c shows a color image after Gaussian filtering to tell the temperature difference on the panel. It reveals that the hot spot is at about 54 \({}^{\circ}\)C. Panel frames are at the temperature of 40 \({}^{\circ}\)C while the rest of the panel is at around 45 \(\sim\) 49 \({}^{\circ}\)C. Figure 11d shows a histogram of the temperature distribution. The PDF curve still looks like a beta distribution function and the bump with 40 \({}^{\circ}\)C is contributed by frames of the panel. The mean temperature is 44 \({}^{\circ}\)C with the deviation of \(-\)10 \({}^{\circ}\)C. The maximum temperature is 54 \({}^{\circ}\)C and the minimum temperature is 30 \({}^{\circ}\)C. In addition, there is a clear bump at 54 \({}^{\circ}\)C, which is a defect caused by hot spots. At the same time, Figure 11e displays the cumulative temperature distribution that the percentage of hot spot area over 50 \({}^{\circ}\)C is 3.2%, indicating there are two cells exceeding the temperature threshold. Finally, Figures 5e and 11e are superimposed in Figure 11f for comparing normal and abnormal conditions.