Ngoc Hai Vu

Optical Fiber Daylighting System Combined with LED Lighting and CPV based on Stepped Thickness Waveguide for Indoor Lighting

We present a design and optical simulation of a cost-effective hybrid daylighting/LED system composed of mixing sunlight and light-emitting diode (LED) illumination powered by renewable solar energy for indoor lighting. In this approach, the sunlight collected by the concentrator is split into visible and non-visible rays by a beam splitter. The proposed sunlight collector consists of a Fresnel lens array. The non-visible rays are absorbed by the solar photovoltaic devices to provide electrical power for the LEDs. The visible rays passing through the beam splitters are coupled to a stepped thickness waveguide (STW) by tilted mirrors and confined by total internal reflection (TIR). LEDs are integrated at the end of the STW to improve the lighting quality. LEDs’ light and sunlight are mixed in the waveguide and they are coupled into an optical fiber bundle for indoor illumination. An optical sensor and lighting control system are used to control the LED light flow to ensure that the total output flux for indoor lighting is a fixed value when the sunlight is inadequate. The daylighting capacity was modeled and simulated with a commercial ray tracing software (LighttoolsTM). Results show that the system can achieve 63.8% optical efficiency at geometrical concentration ratio of 630. A required accuracy of sun tracking system achieved more than ±0.5o. Therefore, our results provide an important breakthrough for the commercialization of large scale optical fiber daylighting systems that are faced with challenges related to high costs.

Development of daylighting systems with non-imaging concentrator

We present a cost-effective and large scale optical fiber daylighting system using non-imaging optics device such as array of linear Fresnel lenses and stepped-thickness waveguide as concentrator. The stepped-thickness waveguide is an optical component that can redirect focused sunlight from vertical to horizontal and guide light to the optical fiber. Our simulation results demonstrate an optical efficiency of up to 56.4% when the concentration ratio of the system is fixed at 100. The simulation also shows that this design has high tolerance for input angle of sunlight. The high tolerance allows replacing a dual axis sun tracking system with a single axis sun-tracking system as a cost-effective solution. Therefore, our results provide an important breakthrough for the commercialization of optical fiber daylighting systems that are faced with challenges related to high costs.

Flat concentrating photovoltaic using lenslet array with mirror coating

We explored an approach of flat CPV system with lateral displacement solar tacking for residential rooftops by using mirror coated lenslet arrays with square array of solar cells integrated on a transparent PMMA sheet.