Cadmium Use in Photovoltaics
http://www.nrel.gov/pv/cdte/citizen.html
Concerned Citizen
"We shouldn't use cadmium telluride in photovoltaics—there are better technologies."
Cadmium telluride is one of the most promising photovoltaic technologies. CdTe cells have high efficiencies (more than 16% in the laboratory) with a nearly perfect bandgap (1.47 eV) for transforming sunlight into electricity. More than a dozen fabrication techniques can be used to deposit CdTe, including close-spaced sublimation, electrodeposition, vapor transport, and chemical vapor deposition. CdTe is a strong, light-absorbent semiconductor—only about a micron is needed to absorb 90% of the solar spectrum. Because very little active material is used during the manufacturing process and because manufacturers can select their least-cost method, CdTe thin films are potentially very affordable. All of these benefits make cadmium telluride use in photovoltaics highly desirable.
"I could be exposed to dangerous levels of cadmium if I install thin-film PV modules on the roof of my house."
Not true.
Exposure to cadmium is problematic only in larger, repeated doses. The trace amounts of cadmium in a thin-film PV module do not approach toxic levels and are not a cause for concern. A rechargeable nickel cadmium battery contains about 2,500 times more cadmium per kilowatt-hour than does a CdTe module—and the cadmium found in PV modules is inert and sealed better than the cadmium found in NiCd batteries.
"CdTe modules are toxic to the environment, especially if the cadmium were to leach into a landfill."
PV materials are largely encased in glass or plastic and many are insoluble, so the materials pose virtually no risk unless the modules are crushed and ground into a fine powder (a situation unlikely to occur). The material is bonded and sealed and, even if it were to be released, it would be below hazardous levels. Today's CdTe PV modules pass federal leaching criteria for non-hazardous waste, unlike fluorescent lights containing mercury and computer screens containing lead, which do not pass landfill-leaching criteria.
In fact, an EPA study (Spiegel 1995) showed that 1 kW of PV could offset between 600 and 2,300 kg of CO2 per year, as well as substantial amounts of other pollutants. Using a small amount of cadmium in a sealed PV module provides substantial environmental benefits.
"It's dangerous to install cadmium telluride thin-film PV modules on a roof. If the house were to catch fire, the residents would inhale harmful amounts of cadmium."
Preliminary studies at Brookhaven National Laboratory and at the GSF Institute of Chemical Ecology in Germany showed that CdTe releases are unlikely to occur during residential fires. It is unlikely that CdTe will vaporize during residential fires because the flames are not hot enough. Flame temperatures in roof fires range from 800°C to 900°C, and flame temperatures in basement rooms range from 900°C to 1000°C. The melting point of CdTe is 1041°C, and evaporation starts at 1050°C. Sublimation occurs at lower temperatures, but the vapor pressure of CdTe at 800°C is only 2.5 torr (0.003 atm). The melting point of CdS is 1750°C, and its vapor pressure due to sublimation at 800°C is only 0.1 torr.
The fire and other sources of emissions within the burning structure would pose a much greater hazard than any potential Cd emissions from PV systems (Drysdale 1985; Moskowitz and Fthenakis 1990; Patterson, et al. 1994; Steinberger 1997; Thumm, et al. 1994).
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