Investigation of Leakage Currents Depending on the Mounting Situation in Accordance to Amorphous Silicon Modules

System induced degradation can occur depending on the system design of PV power plants. In case of amorphous silicon solar modules this causes e.g. a diffusion of sodium ions from the cover glass into the TCO front contact, followed by a chemical reaction that leads to an irreversible power loss and is called TCO-corrosion. Leakage currents between the cover glass and the electrical connectors can be used as an indicator of the corrosion rate.It is state-of-the-art that a negative potential of the TCO-layer in respect to the cover class (resp. mounting structure) can have an impact on the corrosion process. To avoid corrosion the negative DC pole of the PV-generator has to be grounded. Thus a positive potential occurs between the TCO-layer and the cover glass and the positive charged sodium ions do not migrate into the TCO-layer [2]. In contrast to this, the results of newer studies show that the corrosion occurs for positive potentials, too [3,4]. Consequently the basic objective of this paper is the analysis of leakage currents according to the mounting and grounding situation of amorphous silicon solar modules under outdoor conditions. For this purpose nine amorphous silicon solar modules were mounted with different mounting systems, with backrails and module clamps. Furthermore, an external voltage with negative and positive bias is applied between the mounting system and the short-circuited module connectors. Additionally the influence of an AC potential is investigated. This case may occur due to perturbations of an inverter. The leakage currents were measured and logged continuously.