Investigation of the Design Methodology for Transmission-Freeform Surface Set Mirrors Used in Solar Spectrum Simulators

The homogeneity of irradiation within a solar spectrum simulator is pivotal for the precise assessment of photovoltaic products’ characteristics. This paper explores the challenge posed by sidelobe effects that impede the enhancement of irradiation uniformity in contemporary solar spectrum simulators. The investigation pinpoints the misalignment between the collimation and the uniformity of the light collection mirror assembly, along with the beam smoothing system in the simulator, as the principal contributor to sidelobe effects. To counteract these effects, the study introduces a novel Bessel initial structure for a freeform mirror characterized by enhanced uniform light distribution and collimation properties. Additionally, a joint evaluation metric combining uniformity and collimation is formulated, facilitating a synchronous iterative optimization of multi-parameter freeform mirrors via simulated annealing. The simulations report a 1.93-fold enhancement in the uniformity of the irradiation surface in the solar spectrum simulator after optimizing the freeform mirror ensemble.