Design and fabrication of freeform glass concentrating mirrors using a high volume thermal slumping process

Concentrated photovoltaics (CPV) power is a form of clean and renewable energy. However, the cost of harvesting solar energy is still economically prohibitive as compared to more traditional electricity generation methods such as hydroelectric or fossil fuel power. In this study, an innovative, high volume but low cost thermal slumping process was proposed as an alternative method for manufacturing of glass mirrors for high concentration photovoltaic system. In this paper, first a freeform optical design was performed to create a two-stage concentrator with ±1° acceptance angle and uniform output irradiance. Ray-tracing simulation was performed to evaluate the optical design. A machinable ceramic, MACOR®, was tested as mold material for its preferred mechanical and chemical stability at high temperature conditions. To assist the development of the slumping process, finite element method (FEM) simulation was performed to compensate for the mold design for manufacturing errors in this process. Moreover, surface profile and surface roughness were measured to characterize the thermal slumping process. Different manufacturing parameters were tested to identify the proper slumping conditions. It is discovered that surface roughness of the inner surface of the slumped glass mirror remained unchanged after slumping under a pre-determined soaking temperature. This study established a methodology for low cost, high volume glass optics for possible solar concentrator applications.