ES&H Issues and CdTe Thin-Film-Module Manufacturing
The two leading methods of making CdTe thin films—electrodeposition and vapor transport—use cadmium very efficiently. Less than 1% is wasted in the electrodeposition process, and less than 10% is wasted in the vapor transport process. In both processes, the unused cadmium can be collected and easily handled. Manufacturers have also effectively minimized workers' exposure with engineering controls, personal protective equipment, and work practices. To date, testing and investigations by the Environmental Protection Agency (EPA), Underwriters Laboratories, and others indicate no unusual problems—but the programs and companies involved remain vigilant and active in ensuring safety. Biomonitoring of contaminant levels in workers (i.e., urine samples) is a key defense against chronic toxicity. The results of years of biomonitoring have shown that there are no significant observed increases in levels of worker exposure (Zweibel 1995).
Workers are generally safe from cadmium exposure in the plant partly because the Occupational Safety and Health Administration (OSHA) monitors companies using cadmium in its manufacturing processes and because manufacturers take extensive safety precautions. Because skin contact with cadmium is not known to cause adverse health effects (ATSDR 1999), the risk workers potentially face is exposure from breathing air in which cadmium compounds are present in the forms of fine fumes or particles.
Workers who continually breathe high levels of cadmium can experience health problems. As is the case with many commonly used chemicals, long-term exposure can cause lung damage, kidney disease, and bone damage. According to The Department of Health and Human Services, "cadmium and cadmium compounds may reasonably be anticipated to be carcinogens" (ATSDR 1999).
Of course, accidents can happen in any manufacturing process, and some worry about exposure to cadmium in the case of an accidental release of a cadmium-laced liquid from a bath and the subsequent cleanup process. Fortunately, one-time exposure is usually not a concern (Moskowitz, Zweibel and Fthenakis 1990).
Future ES&H work in the area of CdTe manufacturing will likely focus on the following:
- Handling and recycling waste from material that never makes it into PV modules
- Improving methods for removing materials from thin-film module substrates and refining it for reuse
- Developing thinner CdTe films to further reduce the use of cadmium.
Because standard operating procedures for handling exposure issues are common in industry, well-engineered CdTe facilities pose virtually no threat to workers or neighborhoods, as evidenced by existing facilities.
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