To enhance the concentration ratio and reduce the illumination system dimension in solar indoor illumination system, a planar solar concentrator is first applied in the solar illumination system and shows considerable concentration ratio and optical efficiency. The proposed planar solar concentrator can make adjustment of the number of collectors according to different concentration needs, which promotes the design freedom of solar illumination systems. Simulation results show that the optical efficiency of the system reaches 84.69% at a geometric concentration ratio of 250x. Experimental results show that when the geometric concentration ratios of the planar solar concentrators are 10, 20, 30 and 40, the optical efficiencies are 80.87%, 81.12%, 81.21% and 81.13%, respectively. The proposed design provides a new insight into possible designs of novel solar illumination system. (C) 2019 Elsevier Ltd. All rights reserved.