Temperature and reverse voltage across a partially shaded Si PV cell under hot spot test condition

Abstract

Whether a crystalline Si PV cell in a module would fail in hotspot endurance test under partial shading condition is a practical question to many cell and module manufacturers. Answers to this question are associated with the reverse bias and elevated temperature across a partially shaded cell in a string of a module that is under illumination. This study reveals the reverse bias and temperature. It is found that the temperature has almost a linear relationship with the string length, and the reverse voltage is related to both cell Vpm and string length. The maximum reverse voltage and temperature under given string length and cell Vpm are summarized, which can serve as a pair of criteria to simulate the hot spot test condition to examine individual cell, study its hotspot properties. The elevated temperature can easily reach 130°C, when tested in a 24 cell string that is under short circuit condition during the test. And, the temperature can reach 150°C in a 30 cell string, which may cause permanent damage in module in such a test. Thus, it is cautioned that substantial increase in string length from 24 cells is not a realistic practice.