Solar Optical and Infrared Radiative Properties of Transparent Polymer Films

Abstract

Polymer films are used in various solar energy devices, such as transparent insulation materials, encapsulation of solar cells, windows, substrates for functional layers, etc. In many cases the radiative properties of the films in the solar and infrared range are of importance for the specific application. This paper describes averaged solar optical and infrared radiative properties for various transparent polymer films including different polymer types and film thicknesses. The measurements were performed from the near ultraviolet to the medium infrared, covering the range of interest for calculating solar and thermal radiative transfer through glazings (e.g., transparent insulation). Concerning the solar optical properties, the extinction is dominated by scattering. In general, semicrystalline polymer films show higher solar losses than amorphous polymer films. Furthermore, additives frequently used in commercial polymer films to improve e.g. manufacturing, tear resistance and weathering behaviour also affect the solar optical properties of polymer films. In the medium infrared range, extinction is caused by absorption due to intramolecular bond rotations and vibrations of molecular groups and segments of polymeric chains. For blackbody temperatures from 10 to 100 °C ether-, fluoride-, imide-, sulphoneand siloxane-groups are of major relevance.