Production Process Improvements for the Manufacture of Silicon Photovoltaic Solar Cells

This paper summarizes the results of three-year joint venture between the Northwest Energy Efficiency Alliance (Alliance) and Siemens Solar (SSI) to reduce electrical energy use of Czochralski (CZ) hotzones for growing silicon ingots used to make silicon solar cells. It also discusses a spin-off project with Advanced Silicon Materials LLC (ASiMI) to further reduce embedded energy by developing and certifying dendritic (teardrop) polycrystalline silicon (polysilicon) as an alternative feedstock to CZ rods or granular polysilicon. The first project saved over 50% (25 kilowatt-hours per kilogram) and reduced Argon gas consumption by 85%. The dendritic polysilicon project is expected to reduce process energy by 25% (another 50 to 63 kWh/kg). These two steps of the overall process normally consume 250 to 300 kWh/kg but now they will require only 175 to 200 kWh/kg, an overall reduction of 30%.