Hot spot evaluation of photovoltaic modules

Hot-spot heating occurs in a photovoltaic (PV) module when its operating current exceeds the short-circuit current of a shadowed or faulty cell in a cell-string. This shadowed/faulty cell could overheat due to reverse bias and become a fire or electrical hazard. Currently, there are three different test methods used in the industry to identify and address this issue. These three methods are based on the UL 1703 (intrusive) standard, ASTM E2481-06 (non-intrusive) standard and IEC 61215 (non-intrusive) standard. Comparing and identifying the best test method [in terms of time, cost and complexity] is of great value to the consumers, PV module manufacturers and test laboratories such as ASU-PTL. The objective of this paper is to compare these three methods in order to identify the best test method for the modules composed of low and/or high shunt resistance cells. In this work, 18 modules composed of low and high shunt resistance cells were investigated in each of the test methods. Out of eighteen (9 mono-Si and 9 poly-Si) modules tested, sixteen modules (9 poly-Si and 7 mono-Si) passed the hotspot tests of all the three standards. The other two modules (mono-Si with voltage limited cells) passed in the ASTM and IEC methods, but failed in the UL method. These two failures in the UL method may be explained in terms of standard's worst-case assumption (open-circuited diodes) of non-sharing of the stress current by the installed bypass diodes of the modules and/or the extended test duration required in this standard.