Nondestructive estimation of strength deterioration in photovoltaic backsheets using a portable near infrared spectrometer

Photovoltaic (PV) backsheets composed of polyvinylidene difluoride (PVDF) and polyethylene terephthalate (PET) films were evaluated via principal component analysis (PCA) of near infrared (NIR) spectral datasets obtained using a potable NIR spectrometer. The discrimination of material and the degree of deterioration of the backsheets following heating and humidifying or irradiating with UV light was examined. Multiple linear regression (MLR) analysis was also employed to evaluate the degree of deterioration. The reference values (peel and tensile strength) were obtained via the International Electrotechnical Commission (IEC) 61215 and Underwriters Laboratories (UL) 1703 standard methods. The values of the peel strength and tensile strength after heating/humidifying treatment correlate quite strongly with the NIR predicted values (R2=0.946 and R2=0.973, respectively). These results show that the degree of deterioration of a PV backsheet can be nondestructively and easily determined via NIR spectroscopy.