Design of Free-Form Surface Condenser for Solar Simulator

Shi Liu; Guoxing Zou; Guoyu Zhang; Gang Wang; Jian Zhang; Zongtao Duan; Zhengjie Niu; Taiyang Ren

doi:10.3788/AOS221913

Abstract

Results and Discussions According to the analysis results, the target surface of the developed free-form surface condenser displays a uniform irradiation distribution, which indicates an ideal improvement in the irradiation uniformity of the optical integrator's incident surface. In the design proposal, the generatrix is rotated to obtain the free-form surface condenser. After multiple parameters of the Bézier curve are optimized, the irradiation uniformity within ?60 mm of the target surface of the free-form surface condenser rises from 52% before optimization to 92% (Fig. 7). By contrast, the irradiation nonuniformity of the solar simulator using the free-form surface condenser is significantly lower than that of the solar simulator using the ellipsoidal condenser. In the case of the free-form surface condenser, the irradiation nonuniformity within ?50 mm of the irradiation surface is better than 0.32%, and the irradiation nonuniformity within ?100 mm of the irradiation surface is better than 0.53% (Table 1). When the surface accuracy of the free-form surface condenser is controlled within ±15 μm (Fig. 12), the axial position deviation is controlled within 0.3 mm (Fig. 13), the vertical-axis position deviation is controlled within 0.3 mm (Fig. 14), and the angle deviation is controlled within 0.4° (Fig. 15), the irradiance within ?100 mm of the irradiation surface of the solar simulator can be greater than S₀, and the irradiation nonuniformity is less than 1.5%.Objective

The solar simulator is a device that simulates solar irradiation characteristics indoors. In the design of the solar simulator, the irradiation uniformity is an important indicator, which directly determines the accuracy of the device. Hence, improving irradiation uniformity has become a key research direction. In a solar simulator, the concentrator system is one of the key components, which typically uses an ellipsoidal condenser. By the ellipsoidal condenser, the radiation flux from the light source placed on the first focal plane will be focused on the second focal plane. As a result, a convergent spot is formed on the incident surface of the optical integrator, which is dense at the center, sparse at the edge, and Gaussian in shape. This uneven illuminance distribution is detrimental to the irradiation uniformity of the entire system. To address the poor performance of the solar simulator due to the low irradiation uniformity of the optical integrator's incident surface, this paper proposes and designs a free-form surface condenser as the concentrator system of the solar simulator. On the premise that the focusing efficiency is ensured, the irradiation uniformity on the second focal plane is effectively improved as the irradiation uniformity of the solar simulator is improved through better irradiation distribution on the optical integrator's incident surface.

Methods

In this paper, the free-form surface condenser used in the solar simulation system is studied. First, the mapping relationship between the outgoing angle of the light source and the corresponding point on the target surface is determined. According to Fresnel's law and the mapping relationship, the differential equation is derived, which is solved by the Runge-Kutta method to calculate the discrete point data. After curve fitting of the discrete point data, the bus line of the free-form surface condenser is obtained. Second, the generatrix of the free-form surface is generated by the Bézier curve. A simulated annealing algorithm is employed to conduct feedback-oriented optimization on the free-form surface condenser with an extended light source. Third, the optical system of the solar simulator is modeled by the software LightTools, and the ellipsoidal condenser and the free-form surface condenser are configured in the same optical system of a solar simulator for comparative analysis. Fourth, the irradiance and the irradiation nonuniformity within ?100 mm of the irradiation surface are taken as the evaluation indexes, and error simulation analyses are performed to investigate the influence of surface accuracy, axial position offset, vertical-axis position offset, and angle offset of the free-form surface condenser on the irradiance and the irradiation nonuniformity.

Conclusions

In this paper, a free-form surface condenser is proposed and designed. The point light source model is used to construct a reasonable initial structure according to the law of conservation of energy, the edge light theory, and the mapping method. In the design proposal, the generatrix of the free-form surface condenser is represented by the Bézier curve. The parameters of the Bézier curve are selected as the optimization variables, and the irradiation uniformity on the target surface is selected as the evaluation function. In the meantime, a simulated annealing algorithm is used to optimize the free-form surface with an extended light source. The simulation results of LightTools show that the irradiation uniformity on the irradiation surface of the solar simulator is significantly improved when the free surface condenser is used. The irradiation nonuniformity within ?50 mm of the irradiation surface is better than 0.32%, and that within ?100 mm of the irradiation surface is better than 0.53%. When the surface and pose errors of the free-form surface condenser are taken into account according to the existing processing, assembly, and adjustment level, the irradiance greater than S₀ is considered feasible on the irradiation surface, and the irradiation nonuniformity is less than 1.5%. This verifies the feasibility of the processing, detection, assembly, and adjustment of the free-form surface condenser.