Source: NREL, USA
Yes! When PV replaces burning coal for electricity generation, it will prevent a minimum of 2 g of Cd in gaseous emissions and about 140 g of Cd in ash form for each GWh of electricity produced.
Coal burning routinely generates Cd because coal contains Cd. A typical U.S. coal-power plant will generate waste in the form of fine dust or cake (containing about 140 g of Cd) for every GWh of electricity produced. In addition, a minimum of 2 g of Cd will be emitted from the stack (for plants with perfectly maintained electrostatic precipitators or baghouses operating at 98.6% efficiency, and median concentration of Cd in U.S. coal of 0.5 ppm). Power plants with less efficient pollution controls will produce more Cd in gaseous form. Furthermore, a typical U.S. coal-power plant emits about 1,000 tons of CO2, 8 tons of SO2, 3 tons of NOx, and 0.4 tons particulates per GWh of electricity produced. All of these emissions will be reduced when PV offsets coal-burning for some fraction of electricity generation.
Electric Power Research Institute (EPRI). (2002). PISCES database for U.S. power plants and U.S. coal, copyright EPRI 2002.
Source: NREL, USA
Cadmium is a by-product of zinc, lead, and copper mining. Its major feedstock, sphalerite (ZnS), contains only 0.25% cadmium. Because Zn is produced in large quantities (8 million metric tons in 1999), substantial amounts of cadmium are produced as a by-product (no matter how much cadmium is used in the PV industry). This cadmium by-product can be put to beneficial use in PV modules or other products, or it can be discharged into the environment. When the market does not absorb the Cd generated by metal smelters/refiners, it is cemented and buried, stored for future use, or disposed of in landfills as hazardous waste.
Morrow, H. (17 January 2003). Personal communication. The International Cadmium Association.
Plachy, J. (2001). U.S. Geological Survey Minerals Yearbook, Chapter 17: Cadmium.
United States Geological Survey (USGS). Table 6: U.S. statistics for zinc. (Excel 27 KB). Accessed January 6, 2003.
Cadmium is released into the environment from phosphate fertilizers, burning fuels, mining and metal processing operations, natural sources, cement production, and disposing of metal products. Releases from disposed cadmium products, including NiCd batteries, are minor contributors to human exposures because Cd is encapsulated in their structure. Most human cadmium exposure comes from ingestion of food, and most of that stems from the uptake of cadmium by plants from fertilizers, sewage sludge, manure, and atmospheric deposition. Van Assche (1998) has developed a model for human exposure to cadmium and allocated this exposure to these sources. The assumptions and the data inputs for the model are based on actual data from Belgium and the European Community (ERL, 1990; OECD, 1994). The model estimates of the relative importance of various cadmium sources to human exposure are shown in Table 1.
Table 1. Sources and Relative Contributions of Cd Exposure to Humans (in Europe)
Fossil fuel combustion
Iron and steel production
Eliminating CdTe from PV manufacturing because of Cd exposure concerns makes little sense from a broader perspective because 1) as shown from the data above, phosphate fertilizers, fossil fuel combustion, and other industrial activities contribute far more to human cadmium exposure than the production, use, and disposal of cadmium in PV modules; 2) from a broad perspective, the CdTe used in PV manufacturing generates little concern relative to their sources of exposure; and 3) CdTe PV can contribute to reducing other, larger forms of exposure such as fossil fuel combustion (see below for more on this).
Environmental Resources Limited (ERL). (February 1990). Evaluation of the Sources of Human and Environmental Contamination by Cadmium. Prepared for the Commission of the European Community, Directorate General for Environment, Consumer Protection and Nuclear Safety, London.
Organization for Economic Co-operation and Development (OECD). (1994). Risk Reduction Monograph No. 5: Cadmium OECD Environment Directorate, Paris, France. Van Assche, F. J. (1998). "A stepwise model to quantify the relative contribution of different environmental sources to human cadmium exposure." NiCad '98, Prague, Czech Republic, September 21-22, 1998.
Van Assche, F. J.; Ciarletta, P. (1993). "Environmental exposure to cadmium in Belgium: decreasing trends during the 1980s." Heavy Metals in the Environment Volume 1, pp. 34-37. Toronto, September 1993.
Source: NREL, USA
Over the life of a CdTe module (without recycling) versus the life of a NiCd battery, the PV module uses Cd about 2,500 times more efficiently in producing electricity. (If either or both are recycled, this would improve the efficiency of using the Cd/kWh of output.)
If a size-AA or size-C NiCd battery is recharged about 1,000 times, it produces about 310 Wh/g over its life—2,500 times less than a CdTe PV module. Thus, the value of using Cd in PV is much greater than its value elsewhere in the marketplace.
Leclanche. "The rechargeable batteries".. Accessed January 6, 2003.
Morrow, H. (1998). "The importance on recycling to life cycle analysis of nickel cadmium batteries." Proceedings of the 8th International Nickel Cadmium Battery Conference, Prague, Czech Republic, September 21-22, 1998.
Steatite Group, The. "A comprehensive range of industry-proven NiCd batteries." Accessed January 6, 2003.