Lowering the energy consumption of the chemical vapor deposition polysilicon production process for photovoltaics

Abstract

In this work, we analyze the energy consumption during the chemical vapor deposition (CVD) of polysilicon for Photovoltaic (PV) applications. Through theoretical models describing heat transfer and thermodynamics, computational fluid-dynamics modeling (CFD) and experimental research in a laboratory scale prototype reactor, possible energy savings strategies are identified. Models for radiation, conduction and convection heat losses in Siemens-type reactors are developed, shaping a comprehensive model for heat loss. These models take into account the changing conditions over a deposition process and have been validated through experiments carried out in a laboratory scale reactor. Moreover, CFD modeling results for the laboratory reactor are in agreement with the previous ones. From the above, radiation heat loss is shown to be the greatest responsible for the high energy consumption of these type of reactors (~50% for industrial scale reactors). Also, the use of thermal shields and alternative deposition surfaces to maximize the volumetric deposition rate, such as hollow cylinders, are identified as important energy saving measures; and these are explored both theoretically and experimentally. We have demonstrated that energy consumption reductions per kilogram of silicon in the range of 30% are achievable.