Detailed Description of Current Research Activities
a) Establish the environmental profile of CdTe PV through independent, scientific, data-based analyses in the U.S., Europe and Asia.
Photovoltaic modules may contain small amounts of regulated materials, which vary from one type to another. Consequently, the photovoltaic industry is assessing the environmental impacts of the life cycle of these materials and ways to recycle them. This is part of a pro-active long-term environmental strategy to preserve the environmental friendliness of solar cells. Brookhaven' PV EH&S Research Center and First Solar Ltd., have an ongoing collaboration on recycling research and life cycle assessment. This work succeeded in effective separation of metals in solution and already produced a record of invention; work is in progress at both BNL and the CLCA to economically recover the metals so that they can be re-used in PV manufacturing.
b) Electrochemical recovery of Cd from solution with Cu, Al, Zn, Fe, Na, Ca and Mg
Research on recycling of PV modules and manufacturing waste aims in optimizing the recovery of valuable compounds while minimizing life-cycle emissions and energy use, under the constraint of low cost (e.g. a few cents per watt). The major tasks of our research on CdTe PV are: a) Cleaning of glass from the metals and recycling of glass; b) separation of Te from Cd and other metals and recovery of Te for its value; c) recovery of Cd for re-use or effective sequestration. The modules are crushed in fragments and were subject to hydrometallurgical processing involving leaching, ion exchange separation, precipitation and electrowinning. Low concentration acid solutions were effective in totally leaching cadmium and tellurium out of the glass matrix. We used ion exchange columns in series to separate copper and tellurium from cadmium in solution. Subsequently, we recovered Cd and Te from the corresponding solutions with electrowinning and selective precipitation correspondingly. Electrowinning have produced cadmium sheets of 99.5% wt purity in sizes of 2 by 4 cm and 12 by 11 cm. Precipitation of Te in metallic form was obtained by various reduction agents. Ongoing studies aim in improving the purity of the recovered cadmium metal and completing the recovery of tellurium.
c) Comparative LCA of nano- and bulk material for solar cells
This research aims to a) describe the life-cycle environmental profile of the main candidate nanomaterials for photovoltaic (PV) applications; b) compare these profiles with those of the micro-sized counterparts that they may replace, and, c) set out the elements of a process-based approach that will be valuable for comparing nano- to micro- materials within groups of thin-film materials (e.g., semiconductors and superconductors).
Approach: Life Cycle Analysis (LCA) studies have been carried out on bulk materials and processes used for the deposition of silicon and cadmium telluride thin-film solar cells. This work will comprise the baseline of the current analysis. Then, nanotechnology-based innovations that are being researched and tested by the U.S. manufacturers of thin-film PV will be described, mainly under the framework of process-based LCA. Process-specific data are essential for analyzing the subtleties of such emerging technologies. This analysis will be complemented by means of Input Output (EIO) LCA for some sub-stages (e.g., plant equipment, personnel supplies, and office commodities), and will guide us in selecting the system's boundaries for the main process-based analysis. The investigators and their graduate students at Columbia University (CU) will gather information on processes, materials, emissions, and energy requirements from established working relationships with U.S. PV companies and the National Renewable Energy Laboratory (NREL), covering two promising nano-material-based alternatives to existing commercial technologies, (i.e., a-Si and CdTe). We will focus on the effect of changing from the micro-scale to the nano-scale. The CLCA investigators have many years of experience with the environmental aspects of solar energy generation that will be invaluable in defining the real issues and attributes of a nanotechnology-related lifecycle.