A novel, nondestructive low-cost detection method for acetic acid distribution in a photovoltaic (PV) module during the damp heat (DH) test based on reflectance changes of tin film sensors is proposed and demonstrated. The sensor consists of a tin film evaporated on a glass substrate. Nineteen sensors and one gold film are laminated in the PV module, and the DH test was performed at 85°C and 85% relative humidity for 7203 h. The time range of measurement can be controlled between 2000 to 6000 h by adjusting the tin film initial thickness from 70 to 160 nm.

In this study, we evaluated the acetic acid generation in photovoltaic (PV) modules during an accelerated reliability test that combines ultraviolet (UV) irradiation and damp-heat (DH) using tin film sensors. We employed a tin film to detect acetic acid through the change in optical reflectance due to the chemical reaction from metallic tin to transparent tin tetraacetate. The relative reflectance of the tin film sensors laminated in a PV module was measured and used as an indicator of acetic acid generated during the reliability test. Consequently, we achieved non-destructive detection of a small amount of acetic acid generated during the UV irradiation stage of the UV+DH combined test with high spatial and temporal resolution using tin film sensors.