Addressing potential-induced degradation of field-installed PV modules by reducing surface conductivity

Abstract

Potential-induced degradation (PID) has been one of the critical reliability issues in solar photovoltaic (PV) industry last several years. There are several PID mechanisms, but most well-known failure mechanism is the junction shunting, called PID-s. Cell p-n junction is shunted by sodium ion migration from PV module glass, which is due to leakage current caused by high potential difference between solar cell and aluminum frame of the module. Various methods preventing or reducing PID-s have been developed and used by the PV industry; however, those methods can be applied only at the manufacturing plants. We present a method of suppressing or preventing PID by interrupting surface conductivity of the glass, which can be applied to the field installed PV modules. In our previous study, we chose flexible Corning Willow Glass strips with ionomer adhesive to interrupt the surface conductivity of one-cell PV modules and multi-cell commercial PV modules. By applying the flexible Corning Willow Glass strips on the glass surface close to the frame inner edges, we experimentally demonstrated that PID-s can be practically eliminated in the full size commercial modules. In the current study, we investigated the surface conductivity interrupting technique by applying hydrophobic materials (instead of Corning Willow Glass) on the glass surface close to the inner edges of the frame. The module without any hydrophobic material suffered with 29% of power loss after the PID stress test whereas the module with hydrophobic material suffered with only 15% of power loss after the PID stress test. The current investigation indicates that the PID degradation can be significantly reduced using the hydrophobic materials but not eliminated as observed with the flexible Corning Willow Glass.