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Producer-Focused Life Cycle Assessment of Thin-Film Silicon Photovoltaic Systems

  • Author(s): Zhang, Teresa Weirui
  • Advisor(s): Dornfeld, David A
  • et al.
Abstract

Life cycle assessment (LCA) is a powerful environmental management and decision- mak- ing tool that has served the needs of many individual and institutional consumers. Using the example of a thin-film amorphous silicon photovoltaic system, this dissertation work adapts life cycle assessment to best meet the design-for-environment needs of producers.

The producer-focused LCA helps to minimize to the environmental impacts of products by (1) identifying opportunities to reduce environmental impacts, (2) tracking and communi- cating the impacts of design changes, and (3) benchmarking the environmental performance of products with respect to other options on the market. To meet these goals, this dissertation introduces and demonstrates two unique life cycle assessment features - facilities integration and scenario functionality.

Facilities integration is a realistic and dynamic method of attributing the impacts of facilities systems to the corresponding process steps. This is important because facilities impacts are otherwise treated as fixed. This features significantly expands design space available to producers for minimizing environmental impacts in manufacturing.

Scenario functionality is a flexible model structure that allows end users to select from and evaluate a number of different technology, manufacturing, implementation, and model scope options. The feature is useful for two main purposes: (1) to analyze and compare any number of life cycle scenarios, and (2) to adapt model assumptions and scope to mimic that of other studies so that their results can be compared more meaningfully.

This dissertation presents the most comprehensive environmental assessment of thin film silicon photovoltaic (PV) systems to date, employing measured process data of unprece- dented resolution. The cumulative energy demand (CED) and global warming potential (GWP) emissions of an example case, in which manufacturing and installation occur in the United States and the scope includes processes from raw materials to recycling at the end of life, are 2.5 GJ/m2 and 202 kg CO2 eq/m2, corresponding to payback times of 23 and 31 months, respectively. Approximately half the total life cycle impacts occur due to down- stream processes, including balance of system components, transportation, and end of life processing.

A set of results, representing a range of values for 17 different manufacturing and system parameters, is used to identify scenarios yielding the fastest and slowest energy and global warming potential payback times. Thirteen of the parameters are evaluated in a sensitivity analysis, showing that the parameters having the greatest influence on the payback times of the system are energy conversion efficiency, system performance ratio, and characteris- tics of electricity offset during the life of the PV system. The characteristics of electricity offset are parameters that are not widely recognized as having such great influence, and if recognized, may persuasively illustrate the advantages of adopting PV and other renewable energy technologies in areas utilizing inefficient or highly polluting energy sources.

Finally, this dissertation presents a robust, top-down methodology for quantifying the environmental impact of a worker-hour of industrial human labor. Labor is a necessary component of any manufacturing system, and a major source of economic and logistical variance, yet is typically omitted as a factor in the environmental impacts of manufacturing systems. The methodology is applied to quantify the energy consumption, global warming potential, and water withdrawals of an industrial worker-hour in the US as 63 MJ, 4.6 kg CO2 eq, and 82 gallons per worker-hour, respectively . Energy and GWP costs per worker-hour are given, including and excluding the effects of international trade, for 20 major manufacturing countries.

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