Design and construction of active daylighting system using two-stage non-imaging solar concentrator

Since lighting accounts for 20% of global electricity consumption in buildings, daylighting system is an important solution to achieve energy savings in lighting and to reduce carbon dioxide emissions. However, most of the existing fiber-optics daylighting systems are expensive, sensitive to pointing error and complicated in optical design in which multi-stage focusing devices are needed to minimize non-uniformity of focused sunlight. To overcome the aforementioned problems, we propose a novel active daylighting system using two-stage non-imaging solar concentrator (2S-NISC) inspired by our previous experience in non-imaging optics. The 2S-NISC prototype consists of 80 primary facet mirrors with a dimension of 5 cm × 5 cm each, 20 secondary facet mirrors with a dimension of 8 cm × 8 cm each, and densely packed plastic optical fibers as a daylight distribution system. Considering the input solar power of 170 W, the equivalent power conversion efficiency of 2S-NISC prototype is obtained as 22%. For economic analysis, the proposed active daylighting system using 2S-NISC with optimized collective area of 4 m2 is estimated to cost USD 1231.20. Considering the interest rate of 4% and fuel inflation rate of 2%, the total payback period is determined as 6.1 years, which is reasonable because the active daylighting system can last for at least 15 years.