Life Cycle Assessment of Crystalline Silicon Wafers for Photovoltaic Power Generation

A life cycle assessment(LCA) was conducted over the modified Siemens method polycrystalline silicon(S-P-Si) wafer, the modified Siemens method single crystal silicon(S-S-Si) wafer, the metallurgical route polycrystalline silicon(M-P-Si) wafer and the metallurgical route single crystal silicon(M-S-Si) wafer from quartzite mining to wafer slicing in China. A large amount of data was investigated from relevant literature and factories in this study. Based on the contribution analysis and sensitivity analysis, the key points for improvement were found. The result included primary energy demand (PED), chemical oxygen demand (COD), SO2, NH3-N, NOX, CO2, and industrial water use (IWU). The above seven indexes were weighted and then added to get China’s thirteenth five-year plan for energy conservation and emission reduction total environmental impact indexes(ECER-135) of S-P-Si wafer, S-S-Si wafer, M-P-Si wafer and M-S-Si wafer were 1.47 × 10−9, 2.12 × 10−9, 3.30 × 10−10 and 1.22 × 10−9 respectively. The ECER-135 of silicon wafers purified with modified Siemens method was higher than that purified with metallurgical route by 3.1 times on average; the ECER-135 of single crystal silicon wafers production was larger than that of polysilicon wafers production by 2.3 times on average. When the four kinds of silicon wafers were used to generate the same amount of electricity for photovoltaic modules, the ECER-135 of S-P-Si wafer, S-S-Si wafer and M-S-Si wafer were 3.3, 4.5 and 2.8 times of that of M-P-Si wafer respectively. During the whole production process, the electricity consumption was of the highest sensitivity for ECER-135. PED had the highest contribution to the ECER-135 for four kinds of silicon wafers, mainly due to the use of thermal power. If hydropower were used instead of thermal power, the ECER-135 could be reduced by 46% to 62%.