Solar Collector Cover with Temperature-controlled Solar Light Transmittance

Our aim is the development of a solar collector cover with temperature-controlled solar light transmittance in order to protect plastic solar collectors against overheating and to prevent collector damage during stagnation. The temperature-dependent reduction of solar transmittance is based on an increase of backscattering of the incident solar radiation (thermotropism). The thermotropic materials consist of two components: 1) a thermotropic additive, namely submicron-sized core-shell particles containing a phase-change material, and 2) an appropriate transparent matrix polymer. Thermotropic samples based on three different matrix polymers (UV-curable cast resin, EVA and PVB) were prepared as sandwich laminates according to industrially relevant processes. Temperature-dependent measurements of the total solar transmittance reveal absolute differences of up to 28% between OFF and ON state.