Degradation Analysis of 8.65-year-old Polycrystalline Silicon PV Modules under the Weather Conditions of Sana’a – Yemen

Abstract

In 2016, an off-grid PV system (14.64 KW) of (48) multicrystalline silicon (mc-Si) modules were installed on the roof of the Yemen Standardization, Metrology and Quality Control Organization (YSMO) in Sana’a – Yemen. In this work, thirty-eight modules from this system were selected for studying the performance degradation after 8.65 years of operation. Degradation analysis of the selected modules was done using visual inspection and current–voltage (I-V) characterization techniques. Results show that the degradation rates in P_max of the modules under study, over the outdoor exposure period (8.65 years), were found to be between 2.44% and 7.99% with mean of 5.42% and median of 5.24%. By comparing the annual degradation rates with the industry linear warranty based on nominal power of this module, out of the 38 PV modules studied, only 2 modules have been degraded more than 0.7%/year, which implies that these two modules are likely to fail before 25 years in operation under outdoor conditions of Sana’a, Yemen. The remaining 36 PV modules degraded less than 0.7%/year, which are likely to operate reliably for 25 years under outdoor conditions of Sana’a, Yemen. The analysis of electrical performance indicated that the P_max reduction of the studied modules are mainly related to the losses in the I_SC and I_mp. Losses in I_mp can be ascribed to the decreases of the shunt resistance (R_sh). On the other hand, the reduction in I_SC of the modules under study can be correlated to the encapsulation discoloration. The most noticeable visual defect in the studied modules was a discoloring of EVA encapsulant. The encapsulant discoloration reduced the incident photons  that reach the solar cells and thus, decreased the I_SC and output power (P_max) of the modules. Corrosion of the metallisation was also observed in some modules. This defect can lead to reducing the FF of the modules.