Integrated opto-mechanical analysis of a PMMA Fresnel lens for a concentrated photovoltaic system

This study presents the integrated opto-mechanical analysis of a polymethylmethacrylate (PMMA) Fresnel lens used in solar concentrators for concentrated photovoltaic systems. A solid model of a flat Fresnel lens made of PMMA was constructed based on the design parameters and derived formula of a Fresnel lens. Ray-tracing simulations were used to investigate the two main influences of temperature variation on the Fresnel lens: variations in the refractive index and thermal distortion. The temperature dependence of the refractive index of the PMMA lens was analyzed based on the temperature coefficient of the refractive index (dn/dT). The thermal distortion of the Fresnel lens at various temperature increases was calculated using finite element analysis. The temperature-induced effects, refractive index variation, and deformed lens geometry were then simultaneously imported into a ray-tracing simulation. Thus, this study investigates and discusses the thermal-optical effects of a flat Fresnel lens on its optical performance, including the spot size, the maximum irradiance on the receiver, and the optical efficiency at different temperature increases.