• Energy Research

Abstract A novel prototype of two-stage non-imaging solar concentrator (2S-NISC) for active daylighting in a building has been constructed and presented in our previous paper. In this work, the optical characteristics of the 2S-NISC have been explored to analyze the overall performance embracing maximum solar concentration ratio, percentage of energy in uniform illumination area, spillage loss, tolerance angle towards tracking error etc. using analytical formulas assisted by ray-tracing software based on designed parameters including the focal distance, f/D ratio and size of the receiver. In our simulation, we consider the case of 2S-NISC consisted of eighty primary facet mirrors of 5 cm × 5 cm each, twenty secondary facet mirrors of 8 cm × 8 cm each, and plastic optical fibers as a daylight transmitter. When focal distance is changed from 50 to 100 cm, the maximum solar concentration ratio increases from 65.1 to 70.1 suns; whilst the percentage of energy in the uniformly illuminated area shows the overall trend of decreasing when focal distance is changed from 50 to 100 cm except at focal distances 60 cm and 100 cm due to the slope error. Finally, the total tolerance angle of the 2S-NISC that allows at least 95% of energy to be collected with respect to perfect tracking is determined as 0.54˚.

According to the International Energy Agency, nearly 20% of worldwide electricity is used up by lighting. This is equal to the total electricity nuclear power generates. Thus, it is needy to explore new technologies for direct use of sunlight via integrating daylight system to the building, which is cost-saving, environment-friendly, and a green solution rather than indirect conversion of electricity to lighting even from renewable sources. In this paper, we present a review on the existing technologies of daylighting systems up to date and how they can provide lighting in a building interior via collection and distribution of sunlight. Our review is a comprehensive study to embrace both passive daylighting system with stationary design and active daylighting system equipped with sun tracking. The economic feasibility, general challenges, and prospects of daylighting systems are also discussed to understand the existing problems that hinder the extensive deployment of daylighting systems. In conclusion, more research works are needed in improving the technological development of a daylighting system so that it is more affordable, environment-friendly, less energy-intensive, and easy to install and gives uniform illumination for the effective application in both commercial building and residential houses.

Abstract It has been observed that lighting systems consume a significant amount of energy in high-rise buildings even during the daytime. To save power consumption and improve indoor environments, daylighting can be implemented for the interior of buildings by guiding sunlight via optical fibers. In this paper, we propose a new two-stage reflective non-imaging dish concentrator (NIDC) consisted of reflective primary and secondary mirrors that focus sunlight onto high acceptance angle optical fibers located at the target of the concentrator. The optical fibers can guide the concentrated sunlight into the interior area of the building. The new concentrating type of daylighting system was designed, fabricated and evaluated. Under normal sunny day condition with solar irradiance of 1000 W/m2, the calculated average illuminance for our prototype daylighting system with a reflective area of 0.2 m2 is 647.94 lux to illuminate an office area of 6.3 m2, which is also equivalent to illuminate a bigger area of 8.164 m2 based on standard average illumination of 500 lux.

Abstract 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.