Quantification of abrasion-induced ARC transmission losses from reflection spectroscopy

Front side anti-reflective coatings (ARC) provide a significant contribution to performance and energy yield in PV modules, solar thermal housings and green house applications. However, ARC degradation and abrasion may lead to long term losses in optical performance. In order to quantify these losses and bench mark various ARC in abrasion testing, a nondestructive optical assessment of the ARC performance in large samples is required. Here, we present a methodology for the quantitative measurement of front side ARC performance and its impact on optical transmittance from a simple reflection spectroscopy measurement using a commercial spectrometer and a broad band absorber for reflection suppression at the glass back side. Results on reflection spectroscopy are presented on standard ARC coated solar glasses with and without internal reflection suppression, which represent the application scenarios in PV modules and green houses, respectively. The optical transmittance of the front side ARC is calculated via a simplified approach based on the law of energy conservation. A validation is performed by comparing spectra determined with the adapted experimental characterization method with optical calculations. Finally, the simplified method for a quantitative optical front side ARC assessment of full size glass panes is applied in successive and gradual ARC abrasion experiments.