PID - 1,500V readiness of PV modules: Some solutions and how to assess them in the lab

摘要

Even though it is now more than five years since potential-induced degradation (PID) began to proliferate, and despite the fact that solutions are under development, it is currently still the most discussed mode of degradation associated with cracking in PV modules. This is probably because of the serious consequences that can rapidly be triggered when PV systems are affected. Although test specifications have been established (IEC 62804), there is no pass or fail criterion for identifying a PID-free module. This paper presents several ways of addressing the problem of PID at the module and cell levels, by considering glass, encapsulants, thin-film barriers and ion-implanted cells. The proposed solutions are tested in accordance with a specific test protocol, and an applied voltage of 1,500V is used in order to prepare for the future increase in DC plant voltage. An initial PID test was conducted on minimodules at room temperature (25℃ and Al foil), before proceeding to a more severe test at 70℃ (Al foil); this made it possible to clearly differentiate the influences of the different tested materials on PID degradation of the modules. These tests were carried out on 60-cell modules under the following conditions: test duration of 192h, temperature of 75℃, relative humidity of 85% and applied voltage of -1,500V. In contrast to ethylene-vinyl acetate (EVA) and standard glass modules, no evident degradation was observed with thermoplastic polyolefin (TPO), ionomer (ION), and thin chemically tempered glass modules; similarly, no degradation was evident with Al_2O_3-layer (deposited under the SiN layer at the cell level) modules or ion-implanted cell modules. The use of one of these components can therefore be a potential solution to the problem of PID.