Does the compound CdTe pose the same health risk as elemental Cd
Source: NREL, USA
Although long-term exposure to elemental cadmium, a carcinogen, can have detrimental effect on kidneys and bones, limited data exist on CdTe toxicology. However, CdTe is more stable and less soluble than elemental Cd and therefore is likely to be much less toxic. Although the Occupational Safety & Health Administration (OSHA) does not make this distinction, as a general rule, all facilities working with such compounds are encouraged to control the indoor concentrations of CdTe dust or fumes to below the Permissible Exposure Level-Time Weighted Average (PEL-TWA) Cd concentration of 0.005 mg/m3.
The U.S. CdTe PV industry is vigilant in preventing health risks and has established proactive programs in industrial hygiene and environmental control. Workers' exposure to cadmium compounds in PV manufacturing facilities is controlled by rigorous industrial hygiene practices and is continuously monitored by medical tests, thus minimizing health risks.
References
Fthenakis, V.; Morris, S.; Moskowitz, P.; Morgan, D. (1999). "Toxicity of cadmium telluride, copper indium diselenide, and copper gallium diselenide." Progress in Photovoltaics, 7, pp. 489-497.
Bohland, J.; Smigielski, K. (September 2000). First Solar's CdTe module manufacturing experience: environmental, health, and safety results. Proceedings of the 28th IEEE Photovoltaic Specialists Conference, Anchorage, AK.
Do CdTe modules present health risks during a fire
Source: NREL, USA
The flame temperature in typical U.S. residential fires is not high enough to vaporize CdTe. Flame temperatures in roof fires range from 800o-900o C, aand flame temperatures in basement rooms range from 900o-1000o C.1 The melting point of CdTe is 1041oC, and evaporation starts at 1050oC. Sublimation occurs at lower temperatures, but the vapor pressure of CdTe at 800oC is only 2.5 torr (0.003 atm). The melting point of CdS is 1750oC, and its vapor pressure due to sublimation at 800oC is only 0.1 torr. Preliminary studies at Brookhaven National Laboratory2 and at the GSF Institute of Chemical Ecology in Germany3 showed that CdTe releases are unlikely to occur during residential fires or during accidental breakage.4 The thin layers of CdTe and CdS are sandwiched between the glass plates, and at typical flame temperatures (800o-1000oC), these compounds would be encapsulated inside the molten glass, so any Cd vapor emissions are unlikely.
References
1. Drysdale, D. (1985). An Introduction to Fire Dynamics, pp. 329-330, Wiley, NY.
2. Moskowitz, P; Fthenakis, V. (1990). Toxic materials released from photovoltaic modules during fires; health risks, Solar Cells, 29, pp. 63-71.
3. Thumm, W.; Finke, A.; Nuemeier, B.; Beck, B.; Kettrup, A.; Steinberger, H.; Moskowitz, P. (1994). "Environmental and health aspects of CIS-module production, use, and disposal." Presented at the First World Conference on Photovoltaic Energy Conversion, Waikoloa, Hawaii, 5-9 December 1994.
4. Steinberger, H. (1997). HSE for CdTe and CIS thin film module operation, IEA expert workshop "Environmental aspects of PV power systems," May 23, 1997, Report No. 97072, Niewlaar E. and Alsema E. (ed.), Utrecht University, The Netherlands.
5. Patterson, M.; Turner, A.; Sadeghi, M.; Marshall, R. (1994). "HSE aspects of the production and use of CdTe thin film modules." Presented at the 12th European PV Solar Energy Conference, Amsterdam.
Can the CdTe in PV modules harm our health or the environment
Source: NREL, USA
Toxic compounds cannot cause adverse health effects unless they enter the body in harmful doses. The only means by which people might be exposed to compounds from a finished PV module are by accidentally ingesting flakes or dust particles or inhaling dust and fumes. The thin CdTe/CdS layers are stable and solid and are encapsulated between thick layers of glass. Unless the module is ground to a fine dust, dust particles cannot be generated. The vapor pressure of CdTe at ambient conditions is zero. Therefore, it is impossible for vapors or dust to be generated when using PV modules.
See Question 11 for a discussion of fires as a potential source of exposure.
The only issue of some concern is the disposal of the well-encapsulated, relatively immobile CdTe at the end of the module's useful life. Today's CdTe PV end-of-life or broken modules pass Federal (TCLP-RCRA) leaching criteria for non-hazardous waste. Therefore, according to current laws, such modules could be disposed of in landfills. However, recycling PV modules offers an important advantage, and the industry is considering this as it moves toward large and cost-effective production. The recycling issue is not unique to CdTe. The disposal of current x-Si modules, most of which incorporate Pb-based solder, presents similar concerns. Recycling the modules at the end of their useful life completely resolves any environmental concerns.
References
Bohland, J.; Dapkus, T.; Kamm, K.; Smigielski, K. (1998). "Photovoltaics as hazardous materials: the recycling solution." Proceedings of the 2nd IEEE World Photovoltaic Specialists Conference, pp. 716-719.
Fthenakis V. (2002). "Could CdTe PV modules pollute the environment?" Aug. 2002, Brookhaven National Laboratory, Upton, NY 11973.
Fthenakis, V.; Eberspacher, C.; Moskowitz, P. (1996). "Recycling strategies to enhance the commercial viability of photovoltaics." Progress in Photovoltaics, 4, pp. 447-456. Fthenakis, V.; Gonsiorawski, R. (1999). Lead-free solder technology from ASE Americas, Workshop Report BNL-67536, Oct. 19, 1999, Brookhaven National Laboratory, Upton, NY 11973.
Steinberger, H. (1997). HSE for CdTe and CIS thin film module operation, IEA expert workshop. "Environmental aspects of PV power systems." May 23, 1997, Report No. 97072, Niewlaar E. and Alsema E. (ed.), Utrecht University, The Netherlands.
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