Life Cycle Evaluation Of Metallurgical Polysilicon And Its Photovoltaic System Grid-connected Power Generation

The combustion of traditional fossil fuels has led to a series of environmental issues such as climate change,global warming,air pollution,as well as acid rain.In the deteriorative situation of global energy security and various climate change issues,there is an urgent need to develop renewable energy technologies.At present,solar power generation technology has been massively developed and widely applied.Solar grade multi-crystalline silicon is the core material of solar cells,the pollution of solar energy industry mainly reflects in the production processes of multi-crystalline silicon.In the incessant purification process of metallurgical grade silicon,the high energy consumption and environmental pollutants are inevitable.Life cycle assessment is an evaluation method,which is used to evaluate the environmental influence of products and processes in a whole life cycle including raw material collection,processing,production,packaging,transportation,consumption and recycling,as well as final process.More and more researches are concentrated on analyzing the energy and environment in the life cycle of silicon photovoltaic system at home and abroad,but they just mainly pay attention to the modified Siemens method and Silane method of multi-crystalline silicon photovoltaic system,which do not include all stages of the whole life cycle.In this paper,we developed two life cycle assessment models to research the comparison of environmental impacts in production of solar grade multi-crystalline silicon by Metallurgical method and Modified Siemens,and the life cycle of the grid-connected power generation of multi-crystalline silicon photovoltaic system.Based on which we determined the classification of various environmental impacts,the characterization method and calculation models.According to China’s environmental situation,we built up a localized impact assessment methods and relevant indicator factors,completing the weighted calculation of the integrated energy conservation and emission reduction（ECER-125）of the China’s 12th Five-Year Plan,and the comprehensive index of expert inquiry（ISCP2009）.Through comprehensive calculation and analyses of the entire production process,resource investment,energy consumption,environmental emissions and the comprehensive life-cycle environmental impact in the production process of unit mass of solar grade multi-crystalline silicon（1 kg）with the above mentioned two methods,and quantitative comparison,we determine the main processes and links which affect the environment,so as to find out major research directions and approaches to reduce environmental load.We completed the data list analysis of life cycle and the environmental impact assessment of the 1 MWp metallurgical multi-crystalline silicon photovoltaic power generation system from the whole life cycle of the photovoltaic system,which respectively are production,transportation,installation,operation,maintenance and decommissioning.Calculation results show that the comprehensive index is 3.57×10^-6 in terms of ECER-125 and 1.94×10-5 based on ISCP 2009,respectively.In 30 years of a life cycle,the total primary energy consumption is 1.41×10⁷MJ,the total CO₂ emission is 913.8 t,and the energy recovery period is calculated as 3.06 years.Thus,the energy consumption of power generated by solar multi-crystalline silicon photovoltaic system is much lower than the national average power grid electricity.It will save primary energy of 5.00×10⁸ MJ,industrial water 1.20×10⁸ kg,reduce total emissions of 4.23×10⁷ kg of 7 principal pollutants like CO₂,which is with obvious environmental benefits of energy saving and emission reduction.During the research process,we determined the environmental impact types and stages which make the most contribution to the comprehensive environmental impact.Meanwhile,the main cause of them were traced respectively.We found out the focus of sensitivity analysis from inventory data quality analysis.The sensitivity analysis reveals that aluminum consumption brings the most influence.Fortunately,the process of PV station retirement affects the result significantly by recycling the important materials.The improvement analyses reveal that a more reasonable and ecological design on PV system should be adopted.For example,aluminum frames and aluminum supports should be replaced by more environmental friendly materials,or alternatively increase the recovery rate of aluminum.Designers should try their best to reduce the use of scarce resources and increase the recovery rate of them.Through the comparison of the comprehensive environmental impacts of the two production methods,the metallurgical method is with obvious environmental advantage than modified Siemens method.Among various energy power generation technologies and the environmental impacts of photovoltaic power generation globally,the renewable energy,photovoltaics is with the minimal environmental impact,only 3.33%of coal-fired power generation.And the environmental impact of this method is about 56%-66%of other nations’ non-metallurgical multi-crystalline silicon photovoltaic system power generation.All data referenced in this paper stem from reference articles,experiments and actual production in factories in the period of China’s 12th Five-Year Plan（2011-2015）.Therefore,the research results is with historical stage due to the technical levels at that time.For now,with the rapid development of science and technology in this field.Related data is being updated all the time.Hence,the standard of energy-saving emission reduction will be higher.