Potential induced degradation testing on mini modules with detailed fill factor and shunt analysis

Abstract

Reliability testing for potential-induced degradation (PID) is time consuming, taking hundreds of hours in an environmental test chamber. In order to test multiple module materials and cell types in a given run, it is common to use mini modules with short strings of 1 to 6 solar cells, allowing up to 10 times more modules to be packed into the environmental chamber at once. These small modules can have very high series resistance in the range of 4–5 Ω-cm2 and fill factor below 70%, and this complicates assessment of fill factor degradation and power loss during PID. The effect of this extrinsic series resistance on small modules causes a factor of 2 improvements in measured reliability lifetime, but is unrelated to the PID mechanisms being studied and is not relevant to full-sized modules. Using the Suns-Voc measurement technique is proposed as an improved method so shunting and FF changes can be measured without the effects of the high series resistance. The effects of the shunting and power loss caused by PID can then be more accurately assessed.