Daylighting system via fibers based on two-stage sun-tracking model

•A high precision is achieved by adopting hybrid control strategy.•Suit for high solar concentrating system such as daylighting via fibers.•About 34% of concentrated light can be transported to the underpass.•The device is convenient and cheap for common users. A daylighting system consisting of optical fibers and a sun-tracking model has been developed. The system has a concentrating level of 2500 suns and a tracking precision of better than 0.1° to ensure that the amount of overlap of the focal spot and the entrance face is greater than 80%. The device includes two feedback circles, coarse and fine adjustments, using an angle encoder and a special photodiode array, respectively. The coarse adjustment process relies on predictable a priori information of the sun’s trajectory, and discrete features of the output signals from the photodiode array are used by the control program for the fine adjustment. The system then operates in a predictive control mode and exhibits good tracking performance. The optical transmission efficiency is maintained between 37% and 40%, which is close to the theoretical maximum value of 42%. The fluctuation range of illuminance on the working face is less than 20%, which meets visual demands. Five lenses (100mm in diameter) and five 10-m, 2-mm-diameter plastic optical fibers can provide an illumination of 26.7lx for an underpass (4.6m×4.2m) 10m away. Of a direct normal irradiance of 514W/m2, about 70% of the light illuminates the floor.