Dependency of IAM Losses in Colored BIPV Products on the Refractive Index of Colorants

Measurements of the incidence angle modifier (IAM) of colored PV modules based on inkjet-printed glass have shown differences between colors, which are uncorrelated with the total transmittance and reflectance of the colored glass. In this paper, the complex refractive index of ceramic inks is estimated based on measurements of reflectance and transmittance spectra. These estimates are used in ray-tracing simulations to determine the IAM of coupon-sized PV modules with printed ceramic inks. Comparisons of the simulation results to measured IAMs show a high correlation between the refractive index of colorants and the IAM. Furthermore, estimations of the impact of IAM on performance based on TMY data at different locations are performed. The results indicate that changes in IAM due to sample coloration can lead to annual irradiance losses of up to 5% compared to uncolored glass. These losses are caused by additional reflections at the glass-ink interface according to the Fresnel equations, dependent on the refractive index of the ceramic inks.