The compound parabolic concentrator (CPC) with asymmetric structures has the advantages of eliminating the shading phenomenon of array arrangement, reducing the center of gravity of the integrated system, and having small application site constraints. Additionally, the elimination of vacuum tube gap light leakage can recycle the light that should have escaped from the vacuum interlayer gap and improve the optical efficiency of the concentrator. Based on the existing no light escape CPCs (N-CPCs) with symmetric structures, we design a N-CPC with asymmetric structures, which further improves the optical efficiency of the shell-shaped CPC (SS-CPC) and eliminates the light leakage from its vacuum tube gap. However, the curved concentrating surface of the CPC results in uneven distribution of energy flow density on the heat-absorbing surface and thus a decrease in the efficiency of the photothermal/photovoltaic system, and is not conducive to long-term stable operation of the system. Meanwhile, the curved concentrating surface is expensive and difficult to transport and store, which is not favorable for realizing a wide range of applications. Thus, the construction of a concentrating surface composed of multiple planar mirrors can improve the inhomogeneous energy flow density distribution on the heat-absorbing surface, increase the operating time of the CPC, reduce the manufacturing cost of the concentrating surface, and improve the industrial application potential.

Based on the research results of the existing N-CPCs, we adopt the Monte Carlo ray tracing method and the principle of fringe ray, the geometric calculation method to derive the surface formula, and the design of the reflective surface to eliminate the light escape, and ultimately the mapping software to fit a novel N-CPC with asymmetric structures. Additionally, the 3D model of the concentrator is built to verify the existence of light escape via the optical simulation software. The no light escape multi-section CPC (NM-CPC) is constructed by screening the rotation angle with the smallest N-CPC isotropic planarization error based on program calculations, and the NM-CPC solid face shape is printed by a 3D printer. The reflective film and scale are pasted, and the solar rays are simulated by a laser to verify the reliability of the NM-CPC face structure and the correctness of the theoretical model. Meanwhile, the optical simulation software is employed to calculate the optical efficiency of the NM-CPC, and a program is written to calculate the energy flow density on the heat-absorbing surface and the amount of radiant energy collected in a typical meteorological year.

Inspired by the existing N-CPCs, we design an asymmetric N-CPC [Fig. 1(b)], which is simulated and verified to reflect the light escaping from the vacuum tube to the heat-absorbing surface to improve the optical efficiency of the concentrator system [Fig. 2(a)]. The NM-CPC heat-absorbing surface has more uniform energy flow density distribution and lower peak energy flow density ( Figs. 6 and 7), and superior radiant energy collection in Spring and Autumn (Fig. 8). Additionally, 4.73 mm increase in optical port width within the maximum acceptance angle (Fig. 9), and reflective surface consumables almost similar to SS-CPC, but at 1/4 of the cost (Fig. 10) are presented.

For N-CPCs with symmetric structures, we establish a N-CPC, and then construct a novel NM-CPC by isotropic planarization of curved reflective surfaces from the perspective of practical application engineering. Meanwhile, the solar vacuum tube is employed as the absorber, and the optical performance and energy concentration characteristics are analyzed and discussed by experiments and simulations. Finally, the following conclusions are drawn compared with the SS-CPC of the same specification. The simulation verifies the feasibility of N-CPCs to realize no light escape and provides references for the design of N-CPCs with asymmetric structures. The optical efficiency of NM-CPCs changes more gently at the maximum acceptance angle. The distribution of the energy flow density on the heat-absorbing surface is more uniform, and the peak energy flow density can be reduced by up to 39.1 kW/m². Additionally, a better amount of radiant energy collection is shown in Spring and Autumn. The reflective surface of NM-CPCs not only saves 75% of the energy flow density but also reduces the energy flow density of the heat-absorbing surface. While saving 75.5% of the manufacturing cost, this surface features lower transportation and maintenance difficulties, and good engineering practicability.