Energy efficient room illumination by the redirection of sunlight : new micro structured components

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.

Non tracking daylight systems, which redirect the light from solar altitudes between 15° and 65° deep into rooms without causing glare effects, have been applied successfully in several office buildings recently. These systems are based on specially shaped polymer profiles which are inserted in double glass windows and which are commercialized under the label LUMITOP. Based on these macro structured systems, fixed in the upper area of windows above eyelevel, advanced solutions using micro structured components will be reported. Main objective of this new development is the reduction of material input (e.g. PMMA) and production costs. Additionally, the optical properties and redirection performance of the existing system should be improved. First, ray tracing calculations have been carried out to identify optimum solutions for micro structured components capable of redirecting daylight with high and almost homogeneous efficiency over the relevant angular range of solar altitudes and not showing colour effects. The simulation results show, that by using a combination of micro lenses and micro prisms an almost homogeneous sunlight redirection of about 70% is achieved in the angular range of solar altitudes between 25° and 65°. These results could be confirmed by prototypes fabricated in the highly transparent silicone polymer PDMS. Suitable industrial production processes for large area panels (1400 mm x 400mm x 4mm) are hot embossing in thermoplastic materials like PMMA and UV-embossing in special UV-curing resins. Both processes are under development and the status of the development will be reported.