Life cycle assessment of photovoltaic manufacturing consortium (PVMC) copper indium gallium (di)selenide (CIGS) modules

Abstract

Thin film copper indium gallium (di)selenide (CIGS) photovoltaic (PV) modules show promise for significant growth. The Photovoltaics Manufacturing Consortium (PVMC) is leading research and development of CIGS in New York State. This study presents the results of a life cycle assessment (LCA) study of CIGS technology, currently being advanced by PVMC, and compares the environmental performance of several emerging alternative materials and processes. The results provide manufacturers with an understanding of how to produce CIGS sustainably. The cradle-to-gate LCA study followed the International Standards Organization (ISO) 14040 series. In addition to analyzing CIGS cells, the study evaluated zinc oxysulfide (Zn(O,S)) as an alternative for cadmium sulfide (CdS) for the junction partner, and an integrated cell interconnect (ICI) system as an alternative for the screen printing and stringer. Life cycle inventory data for the CIGS cell and alternatives were obtained from PVMC for the product manufacturing stage. Global Solar Energy, Inc. (GSE), a PVMC member and CIGS manufacturer, provided data for the ICI alternative. This data was supplemented by secondary data, from thinkstep, and modeled in GaBi6. The end-of-life stage was not modeled due to limited inventory data. The results identified the following key drivers of environmental and toxicity impacts from the manufacture of CIGS photovoltaic cells: (i) silver used in the stringer and screen printing processes, (ii) metals comprising the CIGS layer, (iii) surface washing of the stainless steel substrate, and (iv) copper in the cable for the balance of system. In addition, the study found that the zinc oxysulfide alternative had lower overall impacts compared to cadmium sulfide. Substitution of the ICI system also reduced impacts of the CIGS system, by decreasing the silver needed. Finally, comparison of the overall life cycle impact results to similar systems in literature, which focused primarily on greenhouse gas emissions, found that the CIGS system fell in the lower end of the range of estimated global warming impacts. PVMC’s CIGS module impacts are likely lower than those made by other manufacturers due to their use of a stainless steel versus glass substrate and reliance on a relatively clean energy mix in New York State. To further reduce impacts, PVMC may wish to substitute the ICI component for the stringer and screen printing processes, recycle additional waste materials, substitute recycled metals for virgin materials, and substitute the cadmium sulfide with the zinc oxysulfide alternative.