Local parallel resistances of solar cell derived by the thermal image analysis

In this paper, local parallel resistances of solar cells are determined by using thermal imaging analysis data. The electrical measurement and thermal infrared measurement were done for twenty unused and non-encapsulated crystalline cells. The bulk resistance of each cell, i.e. a combination of series resistance and shunt resistance, is determined by its IV characteristic at standard test condition and IV characteristic in the dark. The thermal IR images of reverse biased solar cells are captured under dark conditions. Each cell is vertically hung in the temperature controlled chamber. The electrical–thermal model of a solar cell is proposed and its result is published for the first time. Based on a bulk electrical resistance of each cell, the four approaches to estimate local parallel resistance are presented. From the experimental results, it is found that the effective local parallel resistances calculated by thermal imaging analysis are correlated and comparable with measured resistance of the whole cells. For the best case, the resistance obtained from the local resistance measurements differs from the electrical bulk resistance less than 2%.

► Local parallel resistances of solar cell is derived by thermal image analysis.
► Cells having electrical bulk parameters can have difference in some local areas.
► Parallel resistances calculated from thermal images are correlated with bulk values.
► The difference of calculated resistance and electrical measurement is less than 2%.
► The thermal–electrical resistance model is verified.