Design, analysis and validation of Customised Homocentric Fresnel Collector based on longest wavelength of visible spectrum

The paper presents the design of a Customised Homocentric Fresnel Collector (CHFC) based on the principle of superposition and the longest wavelength of the visible spectrum. A bottom-to-top approach is proposed that uses an individually designed homocentric prism based on visible light at a wavelength of 740 nm. The homocentric prism of the CHFC follows a uniform height method with varying pitch. An area focus is achieved on the plastic optical fibre (POF) bundle inlet without employing any secondary optical element. The CHFC achieves a uniform distribution of concentrated visible spectrum radiation from the Sun with a significant reduction in the hotspot problem. Comparison of the CHFC versus a mid-wavelength-based Fresnel lens shows that the CHFC delivers 9.24% more visible spectrum radiation on the POF bundle inlet. The simulated optical efficiency of the CHFC is 90.6%. Numerical analysis of a CHFC-based daylighting system shows that 331 lm (efficiency of 39.4%) can be delivered via a 10 m long fibre bundle made up of 32 POF each of 1 mm diameter. Experimental observations demonstrated that the maximum temperature recorded on the POF bundle entrance is 56.8°C during peak direct normal illuminance conditions. Note that the spectral distribution of the radiation emerging from the POF differs from the incident sunlight spectrum because of the transmission characteristics of the optical components used in the CHFC testbed.