Daylighting in buildings: Developments of sunlight addressing by optical fiber

摘要

In this work is presented a study on the use of the optical fiber and a solar concentrator for a daylighting addressing system in buildings. The solar energy, in the form of light, collected through a sun-tracking parabolic concentrator system, is guided and addressed in the chosen area of the building with an opportune fiber optics guiding structure. A solar lighting system by optical fiber turns out convenient from a point of view of energy saving and in terms of respect of the environment for the resultant reduction in greenhouse gas emissions. Daylighting can, moreover, influence positively the well-being degree: improves visual quality and comfort reducing, for example, the psychological sadness related to the Seasonal Affective Disorder (SAD).The hybrid sunlight addressingear infra-red PV systems under development is composed by a primary parabolic collector (PPC) which concentrates solar light to a secondary flat optical reflector (SOE) made by a series of cold mirrors. These elements are frequency selective, so that only the visible range of the solar spectrum is reflected to "light" optical fiber bundles. The near infra-red part of the solar spectrum is transmitted over to feed photovoltaic cells to get energy for artificial lighting needs at night. By frequency selection the working area of the building is illuminated without the thermal load connected to the infrared portion of the solar radiation. Setting the required ambient light output, with the aid of the principles of the telecommunications antennas, it has been implemented a procedure in MATLAB for sizing of the primary parabolic concentrator and the secondary reflector. It is, therefore, defined the pointof optimal positioning of the circular crown of the bundles of optical fiber. The overall system cost is also estimated. Some considerations on the economic dimensioning of the system in terms of efficiency, estimated annual medium energy saving and expected time of economic amortization are discussed. By the sunlight addressing system described it's possible to avoid the energy "double-conversion". Lighting of building interiors by PV conversion of solar light into electricity and then again into (artificial) light is a low efficiency lighting solution. The direct use of sunlight should be preferred in lighting of rooms with predominant diurnal occupancy, such as classrooms, libraries and laboratories.