With rapid global industrialization, resource exhaustion and global environmental problems have become widespread and critical issues. In order to solve these problems, the use of new and renewable energy has attracted considerable attention. Among renewable energy sources, bioenergy from microalgae is considered to be very promising.
In this thesis, results of the optical design and fabrication of a light-guiding plate (LGP) to be used as an illumination system for photobioreactors are presented. A solar daylighting system was used as the light source for the LGP. This system consists of two parts: a light collector and a light transmitter. The light collector is made up of circular Fresnel lenses and is capable of solar tracking. The light transmitter is composed of plastic optical fibers (POFs) and delivers the sunlight collected by the light collector to the sides of the LGP.
First, we carried out modeling of light sources (exit ports of the POFs), a reflection film, and LGP patterns. Measured illumination distribution was used to model the light source. To model the reflection film, we used measured bidirectional reflective distribution function data. To model the LGP patterns, we assumed that they were Lambertian scatterers. The modeling parameters, i.e., the reflectance R and the scatterer width d of the LGP patterns, were determined by matching simulations with the experimentally measured illuminance distribution of a test LGP and were found to be R = 70% and d = 2.4 mm, respectively.
Next, we designed and fabricated an LGP that was optimized for the average deviation of the illuminance distribution by varying the maximum pattern spacing, minimum pattern spacing, and width of the Gaussian pattern-spacing function. A computerized numerical control (CNC) machine was used for the fabrication. The size of the fabricated LGP was 1000 mm × 500 mm × 10 mm. The measured optical characteristics of average illuminance and uniformity of illuminance distribution were 7,986 lx (photon flux density: 117.6 μΕ/(m2·s)) and 75.4%, respectively.
The LGP designed and fabricated in this work is intended to reduce energy consumption for biomass production. The LGP will be used as an illumination system for a flat-panel photobioreactor developed at the Biorefinery Center, Chosun University, and the overall energy efficiency will be tested.